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<html><head><title>XLISP error</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>error, cerror</h1>
<hr>
<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
<td><nobr>Type:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>function (subr)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xlbfun.c, xldbug.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<p><div class="box">
<dl>
<dt>(<b>error</b> <i>err-msg</i> [<i>arg</i>])</dt>
<dd><i>err-msg</i> - a string expression for the error message<br>
<i>arg</i> - an optional argument expression, printed after the error message<br>
returns - never returns</dd>
</dl>
<dl>
<dt>(<b>cerror</b> <i>cont-msg err-msg</i> [<i>arg</i>])</dt>
<dd><i>cont-msg</i> - a string expression for the <a href="continue.htm">continue</a> message<br>
<i>err-msg</i> - a string expression for the error message<br>
<i>arg</i> - an optional argument expression, printed after the error message<br>
returns - <a href="nil.htm">NIL</a> when continued from the
<nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr></dd>
</dl>
</div></p>
<h2>Description</h2>
<p>The 'error' function allows the generation of a
<nobr>non-correctable</nobr> error. <nobr>A non-correctable</nobr> error
requires evaluation of a <nobr><a href="clean-up.htm">clean-up</a></nobr> or
<nobr><a href="top-level.htm">top-level</a></nobr> function from within the
XLISP <nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr>
to return to normal execution. <nobr>The form</nobr> of the message
generated is:</p>
<pre class="example">
<font color="#AA0000">error:</font> <font color="#0000CC">err-msg</font> <font color="#AA0000">-</font> <font color="#0000CC">arg</font>
</pre>
<p>If a <a href="continue.htm">continue</a> function is evaluated within the
<nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr>, then a
an error message is generated:</p>
<pre class="example">
<font color="#AA0000">error: this error can't be continued</font>
</pre>
<p>There is no return from the 'error' function.</p>
<p>The 'cerror' function allows the generation of a correctable error.
<nobr>A correctable</nobr> error can be corrected by some action
within the XLISP <nobr><a href="../manual/xlisp.htm#break-loop">Break
Loop</a></nobr>. <nobr>The form</nobr> of the message generated is:</p>
<pre class="example">
<font color="#AA0000">error:</font> <font color="#0000CC">err-msg</font> <font color="#AA0000">-</font> <font color="#0000CC">arg</font>
<font color="#AA0000">if continued:</font> <font color="#0000CC">cont-msg</font>
</pre>
<p>In the
<nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr>,
forms can be evaluated to correct the error. <nobr>If a</nobr>
<a href="continue.htm">continue</a> function is evaluated within the
<nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr>, then
<a href="nil.htm">NIL</a> is returned from 'cerror'. <nobr>If desired</nobr>, the
<nobr><a href="clean-up.htm">clean-up</a></nobr> and
<nobr><a href="top-level.htm">top-level</a></nobr> forms may be evaluated
to abort out of the
<nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr>.</p>
<p><div class="box">
<p><b>Note:</b> The <a href="global-breakenable.htm">*breakenable*</a>
variable needs to be <nobr>non-<a href="nil.htm">NIL</a></nobr> for 'error',
'cerror' and system errors to be caught by the Nyquist/XLISP
<nobr><a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr>.</p>
</div></p>
<h2>Examples</h2>
<p>Example of a <nobr>non-correctable</nobr> error:</p>
<pre class="example">
> (error "invalid argument" "arg")
<font color="#AA0000">error: invalid argument - "arg"</font>
1> (continue) <font color="#008844">; the 1 before the > indicates a break loop</font>
<font color="#AA0000">error: this error can't be continued</font>
1> (clean-up)
[ back to previous break level ]
> <font color="#008844">; no break loop any longer</font>
</pre>
<p>Example of system generated correctable error:</p>
<pre class="example">
> (symbol-value 'f)
<font color="#AA0000">error: unbound variable - F</font>
<font color="#AA0000">if continued: try evaluating symbol again</font>
1> (setq f 123) <font color="#008844">; the 1 before the > indicates a break loop</font>
123 <font color="#008844">; return value of (setq f 123)</font>
1> (continue)
123 <font color="#008844">; return value of (symbol-value 'f)</font>
> <font color="#008844">; no break loop any longer</font>
</pre>
<p>See also:</p>
<ul>
<li><nobr>Contents → <a href="../manual/contents.htm#debugging-and-error-handling">Debugging and Error Handling</a></nobr></li>
<li><nobr>XLISP 2.0 Manual → <a href="../manual/xlisp.htm#break-loop">Break Loop</a></nobr></li>
<li><nobr>Tutorials → Nyquist → <a href="../tutorials/nyquist.htm#debugger-shortcuts">Debugger Shortcuts</a></nobr></li>
</ul>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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