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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> <html> <!-- Created by GNU Texinfo 6.8, https://www.gnu.org/software/texinfo/ --> <head> <meta http-equiv="Content-Type" content="text/html; charset=utf-8"> <!-- This manual is for GNU Texinfo (version 6.8, 8 June 2021), a documentation system that can produce both online information and a printed manual from a single source using semantic markup. Copyright (C) 1988, 1990-1993, 1995-1999, 2001-2021 Free Software Foundation, Inc. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with no Front-Cover Texts, and with no Back-Cover Texts. A copy of the license is included in the section entitled "GNU Free Documentation License". --> <title>Sample Function Definition (GNU Texinfo 6.8)</title> <meta name="description" content="Sample Function Definition (GNU Texinfo 6.8)"> <meta name="keywords" content="Sample Function Definition (GNU Texinfo 6.8)"> <meta name="resource-type" content="document"> <meta name="distribution" content="global"> <meta name="Generator" content="texi2any"> <meta name="viewport" content="width=device-width,initial-scale=1"> <link href="index.html" rel="start" title="Top"> <link href="Command-and-Variable-Index.html" rel="index" title="Command and Variable Index"> <link href="index.html#SEC_Contents" rel="contents" title="Table of Contents"> <link href="Definition-Commands.html" rel="up" title="Definition Commands"> <link href="Def-Cmd-Conventions.html" rel="prev" title="Def Cmd Conventions"> <style type="text/css"> <!-- a.copiable-anchor {visibility: hidden; text-decoration: none; line-height: 0em} a.summary-letter {text-decoration: none} blockquote.indentedblock {margin-right: 0em} div.display {margin-left: 3.2em} div.example {margin-left: 3.2em} kbd {font-style: oblique} pre.display {font-family: inherit} pre.format {font-family: inherit} pre.menu-comment {font-family: serif} pre.menu-preformatted {font-family: serif} span.nolinebreak {white-space: nowrap} span.roman {font-family: initial; font-weight: normal} span.sansserif {font-family: sans-serif; font-weight: normal} span:hover a.copiable-anchor {visibility: visible} ul.no-bullet {list-style: none} --> </style> </head> <body lang="en"> <div class="section" id="Sample-Function-Definition"> <div class="header"> <p> Previous: <a href="Def-Cmd-Conventions.html" accesskey="p" rel="prev">Conventions for Writing Definitions</a>, Up: <a href="Definition-Commands.html" accesskey="u" rel="up">Definition Commands</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p> </div> <hr> <span id="A-Sample-Function-Definition"></span><h3 class="section">13.7 A Sample Function Definition</h3> <span id="index-Function-definitions"></span> <span id="index-Command-definitions"></span> <span id="index-Macro-definitions_002c-programming_002dlanguage"></span> <span id="index-Sample-function-definition"></span> <p>A function definition uses the <code>@defun</code> and <code>@end defun</code> commands. The name of the function follows immediately after the <code>@defun</code> command and it is followed, on the same line, by the parameter list. </p> <p>Here is a definition from <a data-manual="elisp" href="../elisp/Calling-Functions.html#Calling-Functions">Calling Functions</a> in <cite>The GNU Emacs Lisp Reference Manual</cite>. </p> <blockquote> <dl class="def"> <dt id="index-apply"><span class="category">Function: </span><span><strong>apply</strong> <em>function &rest arguments</em><a href='#index-apply' class='copiable-anchor'> ¶</a></span></dt> <dd><p><code>apply</code> calls <var>function</var> with <var>arguments</var>, just like <code>funcall</code> but with one difference: the last of <var>arguments</var> is a list of arguments to give to <var>function</var>, rather than a single argument. We also say that this list is <em>appended</em> to the other arguments. </p> <p><code>apply</code> returns the result of calling <var>function</var>. As with <code>funcall</code>, <var>function</var> must either be a Lisp function or a primitive function; special forms and macros do not make sense in <code>apply</code>. </p> <div class="example"> <pre class="example">(setq f 'list) ⇒ list (apply f 'x 'y 'z) error→ Wrong type argument: listp, z (apply '+ 1 2 '(3 4)) ⇒ 10 (apply '+ '(1 2 3 4)) ⇒ 10 (apply 'append '((a b c) nil (x y z) nil)) ⇒ (a b c x y z) </pre></div> <p>An interesting example of using <code>apply</code> is found in the description of <code>mapcar</code>. </p></dd></dl> </blockquote> <p>In the Texinfo source file, this example looks like this: </p> <div class="example"> <pre class="example">@defun apply function &rest arguments @code{apply} calls @var{function} with @var{arguments}, just like @code{funcall} but with one difference: the last of @var{arguments} is a list of arguments to give to @var{function}, rather than a single argument. We also say that this list is @dfn{appended} to the other arguments. </pre><pre class="example"> </pre><pre class="example">@code{apply} returns the result of calling @var{function}. As with @code{funcall}, @var{function} must either be a Lisp function or a primitive function; special forms and macros do not make sense in @code{apply}. </pre><pre class="example"> </pre><pre class="example">@example (setq f 'list) @result{} list (apply f 'x 'y 'z) @error{} Wrong type argument: listp, z (apply '+ 1 2 '(3 4)) @result{} 10 (apply '+ '(1 2 3 4)) @result{} 10 (apply 'append '((a b c) nil (x y z) nil)) @result{} (a b c x y z) @end example </pre><pre class="example"> </pre><pre class="example">An interesting example of using @code{apply} is found in the description of @code{mapcar}. @end defun </pre></div> <p>In this manual, this function is listed in the Command and Variable Index under <code>apply</code>. </p> <p>Ordinary variables and user options are described using a format like that for functions except that variables do not take arguments. </p> </div> <hr> <div class="header"> <p> Previous: <a href="Def-Cmd-Conventions.html">Conventions for Writing Definitions</a>, Up: <a href="Definition-Commands.html">Definition Commands</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html" title="Index" rel="index">Index</a>]</p> </div> </body> </html>