100 lines
4.2 KiB
HTML
100 lines
4.2 KiB
HTML
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<!-- This manual documents Guile version 3.0.10.
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Inc.
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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Permission is granted to copy, distribute and/or modify this document
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under the terms of the GNU Free Documentation License, Version 1.3 or
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any later version published by the Free Software Foundation; with no
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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Error Handling (Guile Reference Manual)</title>
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<meta name="description" content="Error Handling (Guile Reference Manual)">
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<meta name="keywords" content="Error Handling (Guile Reference Manual)">
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<link href="index.html" rel="start" title="Top">
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<link href="Concept-Index.html" rel="index" title="Concept Index">
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<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
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<link href="Using-Guile-Interactively.html" rel="up" title="Using Guile Interactively">
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<link href="Interactive-Debugging.html" rel="next" title="Interactive Debugging">
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<link href="REPL-Commands.html" rel="prev" title="REPL Commands">
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Error-Handling">
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<div class="nav-panel">
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<p>
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Next: <a href="Interactive-Debugging.html" accesskey="n" rel="next">Interactive Debugging</a>, Previous: <a href="REPL-Commands.html" accesskey="p" rel="prev">REPL Commands</a>, Up: <a href="Using-Guile-Interactively.html" accesskey="u" rel="up">Using Guile Interactively</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>
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</div>
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<hr>
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<h4 class="subsection" id="Error-Handling-1"><span>4.4.5 Error Handling<a class="copiable-link" href="#Error-Handling-1"> ¶</a></span></h4>
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<p>When code being evaluated from the REPL hits an error, Guile enters a
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new prompt, allowing you to inspect the context of the error.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">scheme@(guile-user)> (map string-append '("a" "b") '("c" #\d))
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ERROR: In procedure string-append:
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ERROR: Wrong type (expecting string): #\d
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Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
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scheme@(guile-user) [1]>
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</pre></div>
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<p>The new prompt runs inside the old one, in the dynamic context of the
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error. It is a recursive REPL, augmented with a reified representation
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of the stack, ready for debugging.
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</p>
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<p><code class="code">,backtrace</code> (abbreviated <code class="code">,bt</code>) displays the Scheme call
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stack at the point where the error occurred:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">scheme@(guile-user) [1]> ,bt
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1 (map #<procedure string-append _> ("a" "b") ("c" #\d))
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0 (string-append "b" #\d)
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</pre></div>
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<p>In the above example, the backtrace doesn’t have much source
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information, as <code class="code">map</code> and <code class="code">string-append</code> are both
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primitives. But in the general case, the space on the left of the
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backtrace indicates the line and column in which a given procedure calls
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another.
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</p>
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<p>You can exit a recursive REPL in the same way that you exit any REPL:
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via ‘<samp class="samp">(quit)</samp>’, ‘<samp class="samp">,quit</samp>’ (abbreviated ‘<samp class="samp">,q</samp>’), or
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<kbd class="kbd">C-d</kbd>, among other options.
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</p>
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</div>
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</body>
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</html>
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