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<head><title>HARD-ERROR.html -- ACL2 Version 3.1</title></head>
<body text=#000000 bgcolor="#FFFFFF">
<h2>HARD-ERROR</h2>print an error message and stop execution
<pre>Major Section: <a href="PROGRAMMING.html">PROGRAMMING</a>
</pre><p>
<code>(Hard-error ctx str alist)</code> causes evaluation to halt with a short
message using the ``context'' <code>ctx</code>. An error message is first printed
using the string <code>str</code> and alist <code>alist</code> that are of the same kind
as expected by <code><a href="FMT.html">fmt</a></code>. See <a href="FMT.html">fmt</a>. Also see <a href="ER.html">er</a> for a macro that provides a
unified way of signaling errors.
<p>
<code>Hard-error</code> has a guard of <code>t</code>. Also see <a href="ILLEGAL.html">illegal</a> for a
similar capability which however has a guard of <code>nil</code> that supports
static checking using <code><a href="GUARD.html">guard</a></code> verification, rather than using dynamic
(run-time) checking. This distinction is illustrated elsewhere:
see <a href="PROG2$.html">prog2$</a> for examples.<p>
Semantically, <code>hard-error</code> ignores its arguments and always returns
<code>nil</code>. But if a call <code>(hard-error ctx str alist)</code> is encountered
during evaluation, then the string <code>str</code> is printed using the
association list <code>alist</code> (as in <code><a href="FMT.html">fmt</a></code>), after which evaluation halts
immediately. Here is a trivial, contrived example.
<pre>
ACL2 !>(cons 3 (hard-error 'my-context
"Printing 4: ~n0"
(list (cons #\0 4))))<p>
HARD ACL2 ERROR in MY-CONTEXT: Printing 4: four<p>
<p>
ACL2 Error in TOP-LEVEL: Evaluation aborted.<p>
ACL2 !>
</pre>
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