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<head><title>PUSH-UNTOUCHABLE.html -- ACL2 Version 3.1</title></head>
<body text=#000000 bgcolor="#FFFFFF">
<h2>PUSH-UNTOUCHABLE</h2>add name or list of names to the list of untouchable symbols
<pre>Major Section: <a href="EVENTS.html">EVENTS</a>
</pre><p>
<pre>
Examples:
(push-untouchable my-var nil)
(push-untouchable set-mem t)
<p>
General Form:
(push-untouchable name{s} fn-p :doc doc-string)
</pre>
where <code>name{s}</code> is a non-<code>nil</code> symbol or a non-<code>nil</code> true list of
symbols, <code>fn-p</code> is any value (but generally <code>nil</code> or <code>t</code>), and
<code><a href="DOC-STRING.html">doc-string</a></code> is an optional <a href="DOCUMENTATION.html">documentation</a> string not
beginning with ``<code>:doc-section</code> ...''. If <code>name{s}</code> is a symbol it
is treated as the singleton list containing that symbol. The effect
of this event is to union the given symbols into the list of
``untouchable variables'' in the current world if <code>fn-p</code> is
<code>nil</code>, else to union the symbols into the list of ``untouchable
functions''. This event is redundant if every symbol listed is
already a member of the appropriate untouchables list (variables or
functions).<p>
When a symbol is on the untouchables list it is syntactically
illegal for any event to call a function or macro of that name, if
<code>fn-p</code> is non-<code>nil</code>, or to change the value of a state global
variable of that name, if <code>fn-p</code> is <code>nil</code>. Thus, the effect of
pushing a function symbol, <code>name</code>, onto untouchables is to prevent
any future event from using that symbol as a function or macro, or
as a state global variable (according to <code>fn-p</code>). This is
generally done to ``fence off'' some primitive function symbol from
``users'' after the developer has used the symbol freely in the
development of some higher level mechanism.
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