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<html><head>
<title>cl:*multiple-values*</title>
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<a href="../../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../../manual/contents.htm">Contents</a> |
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<a href="../examples.htm">Examples</a> |
<a href="../../reference/reference-index.htm">Reference</a>
<hr>
<h1>cl:*multiple-values*</h1>
<hr>
<p>The <nobr>cl:<b>*multiple-values*</b></nobr> variable is used to signal
if a function has returned multiple values:</p>
<p><div class="box">
<dl>
<dt>cl:<b>*multiple-values*</b></dt>
<dd>returns - <a href="../../reference/t.htm"> T </a> if a
function returned multiple values</dd>
</dl>
</div></p>
<p>Test if a function has returned multiple values:</p>
<pre class="example">
(setf cl:*multiple-values* nil)
(let ((result (function ...)))
(if cl:*multiple-values*
(do-something-with *rslt* ...)
(do-something-with result ...))
... )
</pre>
<p>Do not use <nobr>cl:<b>*multiple-values*</b></nobr> with
<a href="../../reference/let.htm">let</a> like this:</p>
<pre class="example">
(let ((cl:*multiple-values* nil)
(result (function ...)))
(if cl:*multiple-values*
(do-something-with *rslt* ...)
(do-something-with result ...))
... )
</pre>
<p>This doesn't work because 'function' is evaluated in the global XLISP
environment, where the lexical <a href="../../reference/let.htm">let</a>
binding of the <nobr>cl:<b>*multiple-values*</b></nobr> variable does not
exist, while the <a href="../../reference/if.htm"> if </a> form
inside the <a href="../../reference/let.htm">let</a> form cannot see a
global change of the <nobr>cl:<b>*multiple-values*</b></nobr> variable,
because the global value is shadowed by the lexical
<a href="../../reference/let.htm">let</a> binding.
<nobr>See <a href="../environment.htm">Environment</a></nobr> for more
details about variables.</p>
<p>The XLISP <a href="../../reference/progv.htm">progv</a> special form can
be used to encapsulate a multiple value call while automatically restoring
the old values at the end like this:</p>
<pre class="example">
(values 1 2 3) => 1
cl:*multiple-values* => T
*rslt* => (1 2 3)
(progv '(cl:*multiple-values* *rslt*) '(nil nil)
(let ((result (function ...)))
(if cl:*multiple-values*
(do-something-with *rslt* ...)
(do-something-with result ...))))
cl:*multiple-values* => T
*rslt* => (1 2 3)
</pre>
<p><div class="box">
<p><b>Note:</b> All functions returning multiple values set
<nobr>cl:<b>*multiple-values*</b></nobr> to
<a href="../../reference/t.htm"> T </a>, but it's up to the
Lisp programmer to reset the variable
<nobr>to <a href="../../reference/nil.htm">NIL</a></nobr>.</p>
</div></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
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