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<a name="Optional-Arguments"></a>
<div class="header">
<p>
Next: <a href="_0040deffnx.html#g_t_0040deffnx" accesskey="n" rel="next"><code>@deffnx</code></a>, Previous: <a href="Def-Cmd-Continuation-Lines.html#Def-Cmd-Continuation-Lines" accesskey="p" rel="prev">Def Cmd Continuation Lines</a>, Up: <a href="Definition-Commands.html#Definition-Commands" accesskey="u" rel="up">Definition Commands</a> &nbsp; [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Command-and-Variable-Index.html#Command-and-Variable-Index" title="Index" rel="index">Index</a>]</p>
</div>
<hr>
<a name="Optional-and-Repeated-Arguments"></a>
<h3 class="section">14.3 Optional and Repeated Arguments</h3>
<a name="index-Optional-and-repeated-arguments"></a>
<a name="index-Repeated-and-optional-arguments"></a>
<a name="index-Arguments_002c-repeated-and-optional"></a>
<a name="index-Syntax_002c-optional-_0026-repeated-arguments"></a>
<a name="index-Meta_002dsyntactic-chars-for-arguments"></a>

<p>Some entities take optional or repeated arguments, conventionally
specified by using square brackets and ellipses: an argument enclosed
within square brackets is optional, and an argument followed by an
ellipsis is optional and may be repeated more than once.
</p>
<p>Thus, [<var>optional-arg</var>] means that <var>optional-arg</var> is optional
and <var>repeated-args</var><code>&hellip;</code> stands for zero or more
arguments.  Parentheses are used when several arguments are grouped
into additional levels of list structure in Lisp.
</p>
<p>Here is the <code>@defspec</code> line of an example of an imaginary
(complicated) special form:
</p>
<blockquote>
<dl>
<dt><a name="index-foobar"></a>Special Form: <strong>foobar</strong> <em>(var [from to [inc]]) body&hellip;</em></dt>
</dl>
</blockquote>

<p>In this example, the arguments <var>from</var> and <var>to</var> are optional,
but must both be present or both absent.  If they are present,
<var>inc</var> may optionally be specified as well.  These arguments are
grouped with the argument <var>var</var> into a list, to distinguish them
from <var>body</var>, which includes all remaining elements of the
form.
</p>
<p>In a Texinfo source file, this <code>@defspec</code> line is written like
this:
</p>
<div class="example">
<pre class="example">@defspec foobar (var [from to [inc]]) body@dots{}
</pre></div>

<p>The function is listed in the Command and Variable Index under
&lsquo;<samp>foobar</samp>&rsquo;.
</p>




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texinfo-doc-nonfree 6.5.0-1 / usr / share / doc / texinfo / html / Optional-Arguments.html
