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<h2>MV</h2>returning a multiple value
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>Mv</code> is the mechanism provided by ACL2 for returning two or more
values. Logically, <code>(mv x1 x2 ... xn)</code> is the same as
<code>(list x1 x2 ... xn)</code>, a list of the indicated values. However,
ACL2 avoids the cost of building this list structure, with the cost
that <code>mv</code> may only be used in a certain style in definitions: if a
function ever returns using <code>mv</code> (either directly, or by calling
another function that returns a multiple value), then this function
must always return the same number of values.<p>
For more explanation of the multiple value mechanism,
see <a href="MV-LET.html">mv-let</a>.
<p>
ACL2 does not support the Common Lisp construct <code>values</code>, whose
logical meaning seems difficult to characterize. <code>Mv</code> is the ACL2
analogue of that construct.
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