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<html><head><title>XLISP assoc</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="reference-index.htm">Reference</a>
<hr>
<h1>assoc</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>function (subr)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xllist.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<p><div class="box">
<dl>
<dt>(<b>assoc</b> <i>expr a-list</i> [{:test | :test-not} <i>test</i>])</dt>
<dd><i>expr</i> - the expression to find as an atom or list<br>
<i>a-list</i> - the association list to search<br>
<i>test</i> - optional test function (default is <a href="eql.htm">eql</a>)<br>
returns - the alist entry or <a href="nil.htm">NIL</a></dd>
</dl>
</div></p>
<h2>Description</h2>
<p>An association list is a collection of list pairs of the form:</p>
<pre class="example">
((<font color="#0000CC">key1 item1</font>) (<font color="#0000CC">key2 item2</font>) ... (<font color="#0000CC">keyN itemN</font>))
</pre>
<p>The 'assoc' function searches through an association list
'<nobr>a-list</nobr>' looking for the key
<nobr>[a <a href="car.htm">car</a></nobr> in an association pair] that
matches the search 'expr'. <nobr>If a</nobr> match is found, that
association pair is returned as the result. <nobr>If no</nobr> match is
found, <nobr><a href="nil.htm">NIL</a> is</nobr> returned. <nobr>You
may</nobr> specify your own test with the ':test' and
'<nobr>:test-not</nobr>' keywords followed by the 'test' you wish to
perform.</p>
<h2>Examples</h2>
<pre class="example">
(setq mylist '((a . my-a)
(b . his-b)
(c . her-c)
(d . end)))
(assoc 'a mylist) => (A . MY-A)
(assoc 'b mylist) => (B . HIS-B)
(assoc 1 mylist) => NIL
</pre>
<pre class="example">
(setq agelist '((1 (bill bob))
(2 (jane jill))
(3 (tim tom))
(5 (larry daryl daryl))))
(assoc 1 agelist) => (1 (BILL BOB))
(assoc 3 agelist :test #'>=) => (1 (BILL BOB))
(assoc 3 agelist :test #'<) => (5 (LARRY DARYL DARYL))
(assoc 3 agelist :test #'<=) => (3 (TIM TOM))
(assoc 3 agelist :test-not #'>=) => (5 (LARRY DARYL DARYL))
</pre>
<p>Using a list as key, tested with <a href="equal.htm">equal</a>:</p>
<pre class="example">
> (assoc '(a b) '(((c d) e) ((a b) x)) :test #'equal)
((A B) X)
</pre>
<p><b>Note:</b> The 'assoc' function can work with a list or string as the
'expr'. However, the default <a href="eql.htm">eql</a> test does
not work with lists or strings, only symbols and numbers.
<nobr>To make</nobr> this work, you need to use the ':test' keyword along
with <a href="equal.htm">equal</a> <nobr>for 'test'</nobr>.</p>
<p>See also:</p>
<ul>
<li><nobr>Contents → <a href="../manual/contents.htm#list-functions">List Functions</a></nobr></li>
</ul>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
<hr>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
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<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
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