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<html><head>
<title>cl:multiple-value-bind</title>
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<hr>
<h1>cl:multiple-value-bind</h1>
<hr>
<p>The <nobr>cl:<b>multiple-value-bind</b></nobr> macro creates new bindings
for a list of symbols and evaluates expressions that use these bindings:</p>
<p><div class="box">
<dl>
<dt>(cl:<b>multiple-value-bind</b> <i>symbols values</i> [<i>expr1</i> ...])</dt>
<dd><i>symbols</i> - a list of symbols<br>
<i>values</i> - a Lisp expression returning one or more values<br>
<i>exprN</i> - arbitrary Lisp expressions<br>
returns - the value[s] returned by the last expression</dd>
</dl>
</div></p>
<pre class="example">
(defmacro <font color="#0000CC">cl:multiple-value-bind</font> (symbols expr &rest body)
(and (or (not (consp symbols))
(eq 'quote (first symbols))
(dolist (symbol symbols)
(or (symbolp symbol) (return t))))
(error <font color="#880000">"not a list of symbols"</font> symbols))
(setq <font color="#AA5500">cl:*multiple-values*</font> nil)
(let* ((result (eval expr))
(values (if <font color="#AA5500">cl:*multiple-values*</font>
<font color="#AA5500">*rslt*</font>
(list result)))
(number-of-symbols (length symbols))
(number-of-values (length values))
(bindings nil))
(dotimes (index number-of-symbols)
(push (if (< index number-of-values)
(list (nth index symbols)
(list 'quote (nth index values)))
(nth index symbols))
bindings))
(setq bindings (reverse bindings))
`(let ,bindings ,@body)))
</pre>
<p>The 'values' expression is evaluated, and each of the symbols is bound to
the respective value returned by the evaluation. <nobr>If there</nobr> are
more symbols than values returned, extra values of
<a href="../../reference/nilo.htm">NIL</a> are bound to the remaining
symbols. <nobr>If there</nobr> are more values than symbols, the extra
values are ignored. The symbols are bound to the values <nobr>by
<a href="../../reference/let.htm">let</a></nobr>, behaving like an
<nobr>implicit <a href="../../reference/progn.htm">progn</a></nobr>.</p>
<p><nobr>Before evaluating 'expr1', the
<a href="global-multiple-values.htm">cl:*multiple-values*</a></nobr>
variable <nobr>is <a href="../../reference/t.htm"> T </a></nobr>
if evaluating the 'values' expression returned multiple values and
<a href="../../reference/nil.htm">NIL</a> with a normal return value.</p>
<p>The <nobr>cl:<b>multiple-value-bind</b></nobr> macro binds multiple
values to local <a href="../../reference/let.htm">let</a> variables::</p>
<pre class="example">
> (macroexpand-1 '(cl:multiple-value-bind (a b c)
(cl:values 1 2 3)
(list a b c)))
(LET ((A (QUOTE 1))
(B (QUOTE 2))
(C (QUOTE 3)))
(LIST A B C))
</pre>
<p>The <a href="../../reference/quote.htm">quote</a>s are necessary to
prevent 'unbound variable' and 'unbound function' errors with symbols and
lists.</p>
<p>Examples:</p>
<p><b>1.</b> The <nobr>cl:<b>multiple-value-bind</b></nobr> macro binds
values returned by the <a href="values.htm">cl:values</a> function:</p>
<pre class="example">
(defun <font color="#0000CC">multiple-value-function</font> ()
(cl:values 1 2 3)) <font color="#008844">; multiple return values</font>
> (cl:multiple-value-bind (a b c)
(multiple-value-function)
(list a b c))
(1 2 3)
</pre>
<p><b>2.</b> If there are no values returned in the Nyquist
<a href="../../reference/global-rslt.htm">*rslt*</a> variable, the normal
function return value is bound to the first symbol and all remaining symbols
are bound <nobr>to <a href="../../reference/nil.htm">NIL</a></nobr>:</p>
<pre class="example">
(defun <font color="#0000CC">normal-lisp-function</font> ()
(+ 1 1)) <font color="#008844">; normal return value</font>
> (cl:multiple-value-bind (a b c)
(normal-lisp-function)
(list a b c))
(2 NIL NIL)
</pre>
<p><b>3.</b> If there are less values than symbols, the extra symbols are
bound <nobr>to <a href="../../reference/nil.htm">NIL</a></nobr>:</p>
<pre class="example">
(defun <font color="#0000CC">not-enough-values-function</font> ()
(cl:values 1 2)) <font color="#008844">; multiple return values</font>
> (cl:multiple-value-bind (a b c)
(not-enough-values-function)
(list a b c))
(1 2 NIL)
</pre>
<p><b>4.</b> If there are more values than symbols, the extra values are
ignored:</p>
<pre class="example">
(defun <font color="#0000CC">too-many-values-function</font> ()
(cl:values 1 2 3 4 5)) <font color="#008844">; multiple return values</font>
> (cl:multiple-value-bind (a b c)
(too-many-values-function)
(list a b c))
(1 2 3)
</pre>
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