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<html><head><title>XLISP unless</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
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<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>unless</h1>
<hr>
<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
<td><nobr>Type:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>special form (fsubr)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xlcont.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<dl>
<dt>(unless <i>test</i> [<i>expr</i> ... ])</dt>
<dd><i>test</i> - an expression, <a href="nil.htm">NIL</a> or
non-<a href="nil.htm">NIL</a><br>
<i>expr</i> - expressions comprising a body of code<br>
returns - the value of the last expression or
<a href="nil.htm">NIL</a></dd>
</dl>
<h2>Description</h2>
<p>The 'unless' special form executes the 'expr' forms if 'test' evaluates
to a <a href="nil.htm">NIL</a> value. If 'test' is
<nobr><a href="nil.htm">NIL</a> ,</nobr> the value of the last
'expr' is returned as the result. If 'test' is
<nobr>non-<a href="nil.htm">NIL</a> ,</nobr>
<a href="nil.htm">NIL</a> is returned with none of 'expr'
evaluated.</p>
<h2>Examples</h2>
<pre class="example">
(unless NIL) <font color="#008844">; returns NIL</font>
(unless T) <font color="#008844">; returns NIL</font>
(unless NIL (print "hi") 'foo) <font color="#008844">; prints "hi" returns FOO</font>
(unless (listp "a")
(print "not a list")) <font color="#008844">; prints "not a list"</font>
<font color="#008844">; returns "not a list"</font>
</pre>
<p>See the
<a href="../manual/xlisp-man-019.htm#unless">unless</a>
special form in the <nobr>XLISP 2.0</nobr> manual.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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