140 lines
6.6 KiB
HTML
140 lines
6.6 KiB
HTML
<!DOCTYPE html>
|
|
<html>
|
|
<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
|
|
<head>
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
|
<!-- This manual documents Guile version 3.0.10.
|
|
|
|
Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
|
|
Inc.
|
|
|
|
Copyright (C) 2021 Maxime Devos
|
|
|
|
Copyright (C) 2024 Tomas Volf
|
|
|
|
|
|
Permission is granted to copy, distribute and/or modify this document
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
|
any later version published by the Free Software Foundation; with no
|
|
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
|
|
copy of the license is included in the section entitled "GNU Free
|
|
Documentation License." -->
|
|
<title>Pre-Unwind Debugging (Guile Reference Manual)</title>
|
|
|
|
<meta name="description" content="Pre-Unwind Debugging (Guile Reference Manual)">
|
|
<meta name="keywords" content="Pre-Unwind Debugging (Guile Reference Manual)">
|
|
<meta name="resource-type" content="document">
|
|
<meta name="distribution" content="global">
|
|
<meta name="Generator" content=".texi2any-real">
|
|
<meta name="viewport" content="width=device-width,initial-scale=1">
|
|
|
|
<link href="index.html" rel="start" title="Top">
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
|
<link href="Programmatic-Error-Handling.html" rel="up" title="Programmatic Error Handling">
|
|
<link href="Standard-Error-Handling.html" rel="next" title="Standard Error Handling">
|
|
<link href="Catching-Exceptions.html" rel="prev" title="Catching Exceptions">
|
|
<style type="text/css">
|
|
<!--
|
|
a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
|
|
div.example {margin-left: 3.2em}
|
|
span:hover a.copiable-link {visibility: visible}
|
|
strong.def-name {font-family: monospace; font-weight: bold; font-size: larger}
|
|
-->
|
|
</style>
|
|
<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
|
|
|
|
|
|
</head>
|
|
|
|
<body lang="en">
|
|
<div class="subsubsection-level-extent" id="Pre_002dUnwind-Debugging">
|
|
<div class="nav-panel">
|
|
<p>
|
|
Next: <a href="Standard-Error-Handling.html" accesskey="n" rel="next">call-with-error-handling</a>, Previous: <a href="Catching-Exceptions.html" accesskey="p" rel="prev">Catching Exceptions</a>, Up: <a href="Programmatic-Error-Handling.html" accesskey="u" rel="up">Programmatic Error Handling</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
<hr>
|
|
<h4 class="subsubsection" id="Pre_002dUnwind-Debugging-1"><span>6.26.3.2 Pre-Unwind Debugging<a class="copiable-link" href="#Pre_002dUnwind-Debugging-1"> ¶</a></span></h4>
|
|
|
|
<p>Sometimes when something goes wrong, what you want is not just a
|
|
representation of the exceptional situation, but the context that
|
|
brought about that situation. The example in the previous section
|
|
passed <code class="code">#:unwind #t</code> to <code class="code">with-exception-handler</code>, indicating
|
|
that <code class="code">raise-exception</code> should unwind the stack before invoking the
|
|
exception handler. However if you don’t take this approach and instead
|
|
let the exception handler be invoked in the context of the
|
|
<code class="code">raise-exception</code>, you can print a backtrace, launch a recursive
|
|
debugger, or take other “pre-unwind” actions.
|
|
</p>
|
|
<p>The most basic idea would be to simply print a backtrace:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example-preformatted">(define (call-with-backtrace thunk)
|
|
(with-exception-handler
|
|
(lambda (exn)
|
|
(backtrace)
|
|
(raise-exception exn))
|
|
thunk))
|
|
</pre></div>
|
|
|
|
<p>Here we use the built-in <code class="code">backtrace</code> procedure to print the
|
|
backtrace.
|
|
</p>
|
|
<dl class="first-deffn">
|
|
<dt class="deffn" id="index-backtrace-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">backtrace</strong> <var class="def-var-arguments">[highlights]</var><a class="copiable-link" href="#index-backtrace-1"> ¶</a></span></dt>
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fbacktrace_005fwith_005fhighlights"><span class="category-def">C Function: </span><span><strong class="def-name">scm_backtrace_with_highlights</strong> <var class="def-var-arguments">(highlights)</var><a class="copiable-link" href="#index-scm_005fbacktrace_005fwith_005fhighlights"> ¶</a></span></dt>
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fbacktrace"><span class="category-def">C Function: </span><span><strong class="def-name">scm_backtrace</strong> <var class="def-var-arguments">()</var><a class="copiable-link" href="#index-scm_005fbacktrace"> ¶</a></span></dt>
|
|
<dd><p>Display a backtrace of the current stack to the current output port. If
|
|
<var class="var">highlights</var> is given it should be a list; the elements of this list
|
|
will be highlighted wherever they appear in the backtrace.
|
|
</p></dd></dl>
|
|
|
|
<p>By re-raising the exception, <code class="code">call-with-backtrace</code> doesn’t actually
|
|
handle the error. We could define a version that instead aborts the
|
|
computation:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example-preformatted">(use-modules (ice-9 control))
|
|
(define (call-with-backtrace thunk)
|
|
(let/ec cancel
|
|
(with-exception-handler
|
|
(lambda (exn)
|
|
(backtrace)
|
|
(cancel #f))
|
|
thunk)))
|
|
</pre></div>
|
|
|
|
<p>In this second example, we use an escape continuation to abort the
|
|
computation after printing the backtrace, returning <code class="code">#f</code> instead.
|
|
</p>
|
|
<p>It could be that you want to only print a limited backtrace. In that
|
|
case, use <code class="code">start-stack</code>:
|
|
</p>
|
|
<div class="example">
|
|
<pre class="example-preformatted">(use-modules (ice-9 control))
|
|
(define (call-with-backtrace thunk)
|
|
(let/ec cancel
|
|
(start-stack 'stack-with-backtrace
|
|
(with-exception-handler
|
|
(lambda (exn)
|
|
(backtrace)
|
|
(cancel #f))
|
|
thunk))))
|
|
</pre></div>
|
|
|
|
<p>There are also more powerful, programmatic ways to walk the stack using
|
|
<code class="code">make-stack</code> and friends; see the API described in <a class="ref" href="Stacks.html">Stacks</a> and
|
|
<a class="ref" href="Frames.html">Frames</a>.
|
|
</p>
|
|
|
|
</div>
|
|
<hr>
|
|
<div class="nav-panel">
|
|
<p>
|
|
Next: <a href="Standard-Error-Handling.html">call-with-error-handling</a>, Previous: <a href="Catching-Exceptions.html">Catching Exceptions</a>, Up: <a href="Programmatic-Error-Handling.html">Programmatic Error Handling</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html" title="Index" rel="index">Index</a>]</p>
|
|
</div>
|
|
|
|
|
|
|
|
</body>
|
|
</html>
|