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<html><head><title>XLISP cond</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
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<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>cond</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>(cond [(<i>pred1 expr1</i>) [(<i>pred2 expr2</i>) ... ]])</dt>
<dd><i>predN</i> - a predicate <nobr>(<a href="nil.htm">NIL</a> /
non-<a href="nil.htm">NIL</a>)</nobr> expression<br>
<i>exprN</i> - an expression<br>
returns - the value of the first expression whose predicate is
non-<a href="nil.htm">NIL</a></dd>
</dl>
<h2>Description</h2>
<p>The 'cond' special form evaluates a series of <nobr>predicate /</nobr>
expression pairs. 'cond' will evaluate each predicate in sequential order
until it finds one that returns a non-<a href="nil.htm">NIL</a>
value. The expression that is associated with the
non-<a href="nil.htm">NIL</a> value is evaluated. The resulting
value of the evaluated expression is returned by 'cond'. If there are no
predicates that return a non-<a href="nil.htm">NIL</a> value,
<a href="nil.htm">NIL</a> is returned by 'cond'. Only one
expression is evaluated, the first one with a
non-<a href="nil.htm">NIL</a> predicate. Note that the predicate
can be a symbol or expression.</p>
<h2>Examples</h2>
<pre class="example">
(cond <font color="#008844">; sample CONDitional</font>
((not T) (print "this won't print"))
( NIL (print "neither will this"))
( T (print "this will print"))
( T (print "won't get here"))) <font color="#008844">; prints "this will print"</font>
(defun print-what (parm)
(cond <font color="#008844">; start of COND</font>
((numberp parm) (print "numeric")) <font color="#008844">; check for number</font>
((consp parm) (print "list")) <font color="#008844">; check for list</font>
((null parm) (print "nil")) <font color="#008844">; check for NIL</font>
(T (print "something")))) <font color="#008844">; catch-all</font>
(print-what 'a) <font color="#008844">; prints "something"</font>
(print-what 12) <font color="#008844">; prints "numeric"</font>
(print-what NIL) <font color="#008844">; prints "nil"</font>
(print-what '(a b)) <font color="#008844">; prints "list"</font>
</pre>
<p>See the
<a href="../manual/xlisp-man-019.htm#cond">cond</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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