1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
|
<html>
<head><title>POSITION.html -- ACL2 Version 3.1</title></head>
<body text=#000000 bgcolor="#FFFFFF">
<h2>POSITION</h2>position of an item in a string or a list, using <code><a href="EQL.html">eql</a></code> as test
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>(Position item seq)</code> is the least index (zero-based) of the
element <code>item</code> in the string or list <code>seq</code>, if in fact <code>item</code> is
an element of <code>seq</code>. Otherwise <code>(position item seq)</code> is <code>nil</code>.
<p>
<code>(Position item lst)</code> is provably the same in the ACL2 logic as
<code>(position-equal item lst)</code>. It has a stronger <a href="GUARD.html">guard</a> than
<code><a href="POSITION-EQUAL.html">position-equal</a></code> because uses <code><a href="EQL.html">eql</a></code> to test equality of <code>item</code>
with members of <code>lst</code>. Its <a href="GUARD.html">guard</a> requires that either <code>lst</code> is a
string, or else <code>lst</code> is a true list such that either <code>(eqlablep item)</code>
or all members of <code>lst</code> are <code><a href="EQLABLEP.html">eqlablep</a></code>. See <a href="POSITION-EQUAL.html">position-equal</a>
and see <a href="POSITION-EQ.html">position-eq</a>.<p>
<code>Position</code> is a Common Lisp function. See any Common Lisp
documentation for more information. Since ACL2 functions cannot
take keyword arguments (though macros can), the ACL2 functions
<code><a href="POSITION-EQUAL.html">position-equal</a></code> and <code><a href="POSITION-EQ.html">position-eq</a></code> are defined to correspond to
calls of the Common Lisp function <code>position</code> whose keyword argument
<code>:test</code> is <code><a href="EQUAL.html">equal</a></code> or <code><a href="EQ.html">eq</a></code>, respectively.
<br><br><br><a href="acl2-doc.html"><img src="llogo.gif"></a> <a href="acl2-doc-index.html"><img src="index.gif"></a>
</body>
</html>
|
