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<html><head>
<title>cl:multiple-value-setq</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-value-setq</h1>
<hr>
<p>The <nobr>cl:<b>multiple-value-setq</b></nobr> macro assigns multiple
values to multiple variables:</p>
<p><div class="box">
<dl>
<dt>(cl:<b>multiple-value-setq</b> <i>symbols expr</i>)</dt>
<dd><i>symbols</i> - a list of symbols<br>
<i>expr</i> - a Lisp expression returning one or more values<br>
returns - the primary value returned by evaluating the expression</dd>
</dl>
</div></p>
<pre class="example">
(defmacro <font color="#0000CC">cl:multiple-value-setq</font> (symbols expr)
(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))
(assignments (list 'setq)))
(dotimes (index number-of-symbols)
(push (nth index symbols) assignments)
(push (when (< index number-of-values)
(list 'quote (nth index values)))
assignments))
(setq assignments (reverse assignments))
`(progn ,assignments ',result)))
</pre>
<p>The expression is evaluated, and each symbol is assigned to the
corresponding value returned by the evaluation. <nobr>If there</nobr> are
more symbols than values returned,
<a href="../../reference/nil.htm">NIL</a> is assigned to the extra symbols.
<nobr>If there</nobr> are more values than symbols, the extra values are
discarded.</p>
<p><nobr>The
<a href="#cl-global-multiple-values">cl:*multiple-values*</a></nobr>
variable <nobr>is <a href="../../reference/t.htm"> T </a></nobr>
if evaluating the expression returns multiple values and
<a href="../../reference/nil.htm">NIL</a> with a normal return value.</p>
<p>The <nobr>cl:<b>multiple-value-setq</b></nobr> macro assigns multiple
values to multiple variables
<nobr>using <a href="../../reference/setq.htm">setq</a>:</nobr></p>
<pre class="example">
> (macroexpand-1 '(cl:multiple-value-setq (a b c)
(cl:values 1 2 3)))
(PROGN (SETQ A (QUOTE 1)
B (QUOTE 2)
C (QUOTE 3))
(QUOTE 1))
</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-setq</b></nobr> macro assigns
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>
> (let ((a 'A) (b 'B) (c 'C))
(cl:multiple-value-setq (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 assigned to the first symbol and all remaining
symbols are assigned
<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>
> (let ((a 'A) (b 'B) (c 'C))
(cl:multiple-value-setq (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
assigned <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>
> (let ((a 'A) (b 'B) (c 'C))
(cl:multiple-value-setq (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>
> (let ((a 'A) (b 'B) (c 'C))
(cl:multiple-value-setq (a b c)
(too-many-values-function))
(list a b c))
(1 2 3)
</pre>
<p><b>5.</b> Symbols not contained in the
<nobr>cl:<b>multiple-value-setq</b></nobr> <nobr>symbol-list</nobr> are not
changed:</p>
<pre class="example">
(defun <font color="#0000CC">multiple-value-function</font> ()
(cl:values 1 2 3)) <font color="#008844">; multiple return values</font>
> (let ((a 'A) (b 'B) (c 'C) (d 'D) (e 'E))
(cl:multiple-value-setq (a b c)
(multiple-value-function))
(list a b c d e))
(1 2 3 D E)
</pre>
<p><b>5.</b> If no bindings exist, new variables will be created:</p>
<pre class="example">
(defun <font color="#0000CC">multiple-value-function</font> ()
(cl:values 1 2 3)) <font color="#008844">; multiple return values</font>
> (let ((c 'C) (d 'D) (e 'E))
(cl:multiple-value-setq (a b c)
(multiple-value-function))
(list a b c d e))
(1 2 3 D E)
</pre>
<p><b>Caution:</b> In the last example, two global variables 'a' and 'b'
were created, while the lexical <a href="../../reference/let.htm">let</a>
variable 'c' was assigned to the <nobr>value 3</nobr>:</p>
<pre class="example">
> (list a b)
(1 2)
> (list a b c)
<font color="#AA0000">error: unbound variable - C</font>
</pre>
<p>The lexical <a href="../../reference/let.htm">let</a> binding of 'c' does
not exist in the global <nobr>top-level</nobr>.
<nobr>See <a href="../environment.htm">Environment</a></nobr> for more
details about variables.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
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