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<a name="Guile-Exception-Handling"></a>
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<hr>
<a name="Guile-Exception-Handling-1"></a>
<h4 class="subsubsection">23.3.3.4 Guile Exception Handling</h4>
<a name="index-guile-exceptions"></a>
<a name="index-exceptions_002c-guile"></a>
<a name="index-set-guile-print_002dstack"></a>

<p>When executing the <code>guile</code> command, Guile exceptions
uncaught within the Guile code are translated to calls to the
<small>GDB</small> error-reporting mechanism.  If the command that called
<code>guile</code> does not handle the error, <small>GDB</small> will
terminate it and report the error according to the setting of
the <code>guile print-stack</code> parameter.
</p>
<p>The <code>guile print-stack</code> parameter has three settings:
</p>
<dl compact="compact">
<dt><code>none</code></dt>
<dd><p>Nothing is printed.
</p>
</dd>
<dt><code>message</code></dt>
<dd><p>An error message is printed containing the Guile exception name,
the associated value, and the Guile call stack backtrace at the
point where the exception was raised.  Example:
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) guile (display foo)
ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.
</pre></div>

</dd>
<dt><code>full</code></dt>
<dd><p>In addition to an error message a full backtrace is printed.
</p>
<div class="smallexample">
<pre class="smallexample">(gdb) set guile print-stack full
(gdb) guile (display foo)
Guile Backtrace:
In ice-9/boot-9.scm:
 157: 10 [catch #t #&lt;catch-closure 2c76e20&gt; ...]
In unknown file:
   ?: 9 [apply-smob/1 #&lt;catch-closure 2c76e20&gt;]
In ice-9/boot-9.scm:
 157: 8 [catch #t #&lt;catch-closure 2c76d20&gt; ...]
In unknown file:
   ?: 7 [apply-smob/1 #&lt;catch-closure 2c76d20&gt;]
   ?: 6 [call-with-input-string &quot;(display foo)&quot; ...]
In ice-9/boot-9.scm:
2320: 5 [save-module-excursion #&lt;procedure 2c2dc30 ... ()&gt;]
In ice-9/eval-string.scm:
  44: 4 [read-and-eval #&lt;input: string 27cb410&gt; #:lang ...]
  37: 3 [lp (display foo)]
In ice-9/eval.scm:
 387: 2 [eval # ()]
 393: 1 [eval #&lt;memoized foo&gt; ()]
In unknown file:
   ?: 0 [memoize-variable-access! #&lt;memoized foo&gt; ...]

ERROR: In procedure memoize-variable-access!:
ERROR: Unbound variable: foo
Error while executing Scheme code.
</pre></div>
</dd>
</dl>

<p><small>GDB</small> errors that happen in <small>GDB</small> commands invoked by
Guile code are converted to Guile exceptions.  The type of the
Guile exception depends on the error.
</p>
<p>Guile procedures provided by <small>GDB</small> can throw the standard
Guile exceptions like <code>wrong-type-arg</code> and <code>out-of-range</code>.
</p>
<p>User interrupt (via <kbd>C-c</kbd> or by typing <kbd>q</kbd> at a pagination
prompt) is translated to a Guile <code>signal</code> exception with value
<code>SIGINT</code>.
</p>
<p><small>GDB</small> Guile procedures can also throw these exceptions:
</p>
<dl compact="compact">
<dt><code>gdb:error</code>
<a name="index-gdb_003aerror"></a>
</dt>
<dd><p>This exception is a catch-all for errors generated from within <small>GDB</small>.
</p>
</dd>
<dt><code>gdb:invalid-object</code>
<a name="index-gdb_003ainvalid_002dobject"></a>
</dt>
<dd><p>This exception is thrown when accessing Guile objects that wrap underlying
<small>GDB</small> objects have become invalid.  For example, a
<code>&lt;gdb:breakpoint&gt;</code> object becomes invalid if the user deletes it
from the command line.  The object still exists in Guile, but the
object it represents is gone.  Further operations on this breakpoint
will throw this exception.
</p>
</dd>
<dt><code>gdb:memory-error</code>
<a name="index-gdb_003amemory_002derror"></a>
</dt>
<dd><p>This exception is thrown when an operation tried to access invalid
memory in the inferior.
</p>
</dd>
<dt><code>gdb:pp-type-error</code>
<a name="index-gdb_003app_002dtype_002derror"></a>
</dt>
<dd><p>This exception is thrown when a Guile pretty-printer passes a bad object
to <small>GDB</small>.
</p></dd>
</dl>

<p>The following exception-related procedures are provided by the
<code>(gdb)</code> module.
</p>
<dl>
<dt><a name="index-make_002dexception"></a>Scheme Procedure: <strong>make-exception</strong> <em>key args</em></dt>
<dd><p>Return a <code>&lt;gdb:exception&gt;</code> object given by its <var>key</var> and
<var>args</var>, which are the standard Guile parameters of an exception.
See the Guile documentation for more information (see <a href="http://www.gnu.org/software/guile/manual/html_node/Exceptions.html#Exceptions">Exceptions</a> in <cite>GNU Guile Reference Manual</cite>).
</p></dd></dl>

<dl>
<dt><a name="index-exception_003f"></a>Scheme Procedure: <strong>exception?</strong> <em>object</em></dt>
<dd><p>Return <code>#t</code> if <var>object</var> is a <code>&lt;gdb:exception&gt;</code> object.
Otherwise return <code>#f</code>.
</p></dd></dl>

<dl>
<dt><a name="index-exception_002dkey"></a>Scheme Procedure: <strong>exception-key</strong> <em>exception</em></dt>
<dd><p>Return the <var>args</var> field of a <code>&lt;gdb:exception&gt;</code> object.
</p></dd></dl>

<dl>
<dt><a name="index-exception_002dargs"></a>Scheme Procedure: <strong>exception-args</strong> <em>exception</em></dt>
<dd><p>Return the <var>args</var> field of a <code>&lt;gdb:exception&gt;</code> object.
</p></dd></dl>

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