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
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
|
<html>
<head><title>DECLARE-STOBJS.html -- ACL2 Version 3.1</title></head>
<body text=#000000 bgcolor="#FFFFFF">
<h2>DECLARE-STOBJS</h2>declaring a formal parameter name to be a single-threaded object
<pre>Major Section: <a href="STOBJ.html">STOBJ</a>
</pre><p>
When a <code><a href="DEFUN.html">defun</a></code> uses one of its formals as a single-threaded object
(<a href="STOBJ.html">stobj</a>), the <code>defun</code> <em>must</em> include a declaration that the
formal is to be so used. An exception is the formal ``<code><a href="STATE.html">state</a></code>,'' which
if not declared as explained below, may still be used provided an
appropriate global ``declaration'' is issued:
see <a href="SET-STATE-OK.html">set-state-ok</a>.
<p>
If the formal in question is <code>counters</code> then an appropriate declaration
is
<pre>
(declare (xargs :stobjs counters))
</pre>
or, more generally,
<pre>
(declare (xargs :stobjs (... counters ...)))
</pre>
where all the single-threaded formals are listed.<p>
For such a declaration to be legal it must be the case that all the names
have previously been defined as single-threaded objects with <code><a href="DEFSTOBJ.html">defstobj</a></code>.<p>
When an argument is declared to be single-threaded the guard of the
function is augmented by conjoining to it the condition that the
argument satisfy the recognizer for the single-threaded object.
Furthermore, the syntactic checks done to enforce the legal use of
single-threaded objects are also sufficient to allow these guard
conjuncts to be automatically proved.<p>
The obvious question arises: Why does ACL2 insist that you declare
stobj names before using them in <code>defun</code>s if you can only declare names
that have already been defined with <code>defstobj</code>? What would go wrong if
a formal were treated as a single-threaded object if and only if it had
already been so defined?<p>
Suppose that one user, say Jones, creates a book in which <code>counters</code>
is defined as a single-threaded object. Suppose another user, Smith,
creates a book in which <code>counters</code> is used as an ordinary formal
parameter. Finally, suppose a third user, Brown, wishes to use both
books. If Brown includes Jones' book first and then Smith's, then
Smith's function treats <code>counters</code> as single-threaded. But if Brown
includes Smith's book first, the argument is treated as ordinary.<p>
ACL2 insists on the declaration to ensure that the definition is
processed the same way no matter what the context.
<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>
|
