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231 lines
11 KiB
HTML
231 lines
11 KiB
HTML
4 years ago
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Copyright (C) 1988-2019 Free Software Foundation, Inc.
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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 the
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Invariant Sections being "Free Software" and "Free Software Needs
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Free Documentation", with the Front-Cover Texts being "A GNU Manual,"
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and with the Back-Cover Texts as in (a) below.
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(a) The FSF's Back-Cover Text is: "You are free to copy and modify
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this GNU Manual. Buying copies from GNU Press supports the FSF in
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developing GNU and promoting software freedom." -->
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<!-- Created by GNU Texinfo 6.4, http://www.gnu.org/software/texinfo/ -->
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<head>
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<title>Guile Pretty Printing API (Debugging with GDB)</title>
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<meta name="description" content="Guile Pretty Printing API (Debugging with GDB)">
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<meta name="keywords" content="Guile Pretty Printing API (Debugging with GDB)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content="makeinfo">
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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<link href="index.html#Top" rel="start" title="Top">
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<link href="Concept-Index.html#Concept-Index" 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="Guile-API.html#Guile-API" rel="up" title="Guile API">
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<link href="Selecting-Guile-Pretty_002dPrinters.html#Selecting-Guile-Pretty_002dPrinters" rel="next" title="Selecting Guile Pretty-Printers">
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<link href="Types-In-Guile.html#Types-In-Guile" rel="prev" title="Types In Guile">
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<style type="text/css">
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pre.smalldisplay {font-family: inherit; font-size: smaller}
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pre.smallexample {font-size: smaller}
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-->
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</style>
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</head>
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<body lang="en">
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<a name="Guile-Pretty-Printing-API"></a>
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<div class="header">
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<p>
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Next: <a href="Selecting-Guile-Pretty_002dPrinters.html#Selecting-Guile-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Guile Pretty-Printers</a>, Previous: <a href="Types-In-Guile.html#Types-In-Guile" accesskey="p" rel="prev">Types In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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<hr>
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<a name="Guile-Pretty-Printing-API-1"></a>
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<h4 class="subsubsection">23.3.3.8 Guile Pretty Printing API</h4>
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<a name="index-guile-pretty-printing-api"></a>
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<p>An example output is provided (see <a href="Pretty-Printing.html#Pretty-Printing">Pretty Printing</a>).
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</p>
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<p>A pretty-printer is represented by an object of type <gdb:pretty-printer>.
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Pretty-printer objects are created with <code>make-pretty-printer</code>.
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</p>
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<p>The following pretty-printer-related procedures are provided by the
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<code>(gdb)</code> module:
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</p>
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<dl>
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<dt><a name="index-make_002dpretty_002dprinter"></a>Scheme Procedure: <strong>make-pretty-printer</strong> <em>name lookup-function</em></dt>
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<dd><p>Return a <code><gdb:pretty-printer></code> object named <var>name</var>.
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</p>
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<p><var>lookup-function</var> is a function of one parameter: the value to
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be printed. If the value is handled by this pretty-printer, then
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<var>lookup-function</var> returns an object of type
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<gdb:pretty-printer-worker> to perform the actual pretty-printing.
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Otherwise <var>lookup-function</var> returns <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-pretty_002dprinter_003f"></a>Scheme Procedure: <strong>pretty-printer?</strong> <em>object</em></dt>
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<dd><p>Return <code>#t</code> if <var>object</var> is a <code><gdb:pretty-printer></code> object.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-pretty_002dprinter_002denabled_003f"></a>Scheme Procedure: <strong>pretty-printer-enabled?</strong> <em>pretty-printer</em></dt>
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<dd><p>Return <code>#t</code> if <var>pretty-printer</var> is enabled.
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Otherwise return <code>#f</code>.
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</p></dd></dl>
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<dl>
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<dt><a name="index-set_002dpretty_002dprinter_002denabled_0021"></a>Scheme Procedure: <strong>set-pretty-printer-enabled!</strong> <em>pretty-printer flag</em></dt>
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<dd><p>Set the enabled flag of <var>pretty-printer</var> to <var>flag</var>.
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The value returned is unspecified.
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</p></dd></dl>
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<dl>
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<dt><a name="index-pretty_002dprinters"></a>Scheme Procedure: <strong>pretty-printers</strong></dt>
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<dd><p>Return the list of global pretty-printers.
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</p></dd></dl>
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<dl>
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<dt><a name="index-set_002dpretty_002dprinters_0021"></a>Scheme Procedure: <strong>set-pretty-printers!</strong> <em>pretty-printers</em></dt>
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<dd><p>Set the list of global pretty-printers to <var>pretty-printers</var>.
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The value returned is unspecified.
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</p></dd></dl>
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<dl>
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<dt><a name="index-make_002dpretty_002dprinter_002dworker"></a>Scheme Procedure: <strong>make-pretty-printer-worker</strong> <em>display-hint to-string children</em></dt>
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<dd><p>Return an object of type <code><gdb:pretty-printer-worker></code>.
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</p>
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<p>This function takes three parameters:
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</p>
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<dl compact="compact">
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<dt>‘<samp>display-hint</samp>’</dt>
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<dd><p><var>display-hint</var> provides a hint to <small>GDB</small> or <small>GDB</small>
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front end via MI to change the formatting of the value being printed.
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The value must be a string or <code>#f</code> (meaning there is no hint).
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Several values for <var>display-hint</var>
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are predefined by <small>GDB</small>:
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</p>
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<dl compact="compact">
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<dt>‘<samp>array</samp>’</dt>
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<dd><p>Indicate that the object being printed is “array-like”. The CLI
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uses this to respect parameters such as <code>set print elements</code> and
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<code>set print array</code>.
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</p>
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</dd>
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<dt>‘<samp>map</samp>’</dt>
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<dd><p>Indicate that the object being printed is “map-like”, and that the
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children of this value can be assumed to alternate between keys and
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values.
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</p>
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</dd>
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<dt>‘<samp>string</samp>’</dt>
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<dd><p>Indicate that the object being printed is “string-like”. If the
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printer’s <code>to-string</code> function returns a Guile string of some
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kind, then <small>GDB</small> will call its internal language-specific
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string-printing function to format the string. For the CLI this means
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adding quotation marks, possibly escaping some characters, respecting
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<code>set print elements</code>, and the like.
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</p></dd>
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</dl>
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</dd>
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<dt>‘<samp>to-string</samp>’</dt>
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<dd><p><var>to-string</var> is either a function of one parameter, the
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<code><gdb:pretty-printer-worker></code> object, or <code>#f</code>.
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</p>
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<p>When printing from the CLI, if the <code>to-string</code> method exists,
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then <small>GDB</small> will prepend its result to the values returned by
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<code>children</code>. Exactly how this formatting is done is dependent on
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the display hint, and may change as more hints are added. Also,
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depending on the print settings (see <a href="Print-Settings.html#Print-Settings">Print Settings</a>), the CLI may
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print just the result of <code>to-string</code> in a stack trace, omitting
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the result of <code>children</code>.
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</p>
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<p>If this method returns a string, it is printed verbatim.
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</p>
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<p>Otherwise, if this method returns an instance of <code><gdb:value></code>,
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then <small>GDB</small> prints this value. This may result in a call to
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another pretty-printer.
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</p>
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<p>If instead the method returns a Guile value which is convertible to a
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<code><gdb:value></code>, then <small>GDB</small> performs the conversion and prints
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the resulting value. Again, this may result in a call to another
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pretty-printer. Guile scalars (integers, floats, and booleans) and
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strings are convertible to <code><gdb:value></code>; other types are not.
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</p>
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<p>Finally, if this method returns <code>#f</code> then no further operations
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are peformed in this method and nothing is printed.
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</p>
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<p>If the result is not one of these types, an exception is raised.
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</p>
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<p><var>to-string</var> may also be <code>#f</code> in which case it is left to
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<var>children</var> to print the value.
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</p>
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</dd>
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<dt>‘<samp>children</samp>’</dt>
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<dd><p><var>children</var> is either a function of one parameter, the
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<code><gdb:pretty-printer-worker></code> object, or <code>#f</code>.
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</p>
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<p><small>GDB</small> will call this function on a pretty-printer to compute the
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children of the pretty-printer’s value.
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</p>
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<p>This function must return a <gdb:iterator> object.
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Each item returned by the iterator must be a tuple holding
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two elements. The first element is the “name” of the child; the
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second element is the child’s value. The value can be any Guile
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object which is convertible to a <small>GDB</small> value.
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</p>
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<p>If <var>children</var> is <code>#f</code>, <small>GDB</small> will act
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as though the value has no children.
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</p></dd>
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</dl>
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</dd></dl>
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<p><small>GDB</small> provides a function which can be used to look up the
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default pretty-printer for a <code><gdb:value></code>:
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</p>
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<dl>
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<dt><a name="index-default_002dvisualizer"></a>Scheme Procedure: <strong>default-visualizer</strong> <em>value</em></dt>
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<dd><p>This function takes a <code><gdb:value></code> object as an argument. If a
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pretty-printer for this value exists, then it is returned. If no such
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printer exists, then this returns <code>#f</code>.
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</p></dd></dl>
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<hr>
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<div class="header">
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<p>
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Next: <a href="Selecting-Guile-Pretty_002dPrinters.html#Selecting-Guile-Pretty_002dPrinters" accesskey="n" rel="next">Selecting Guile Pretty-Printers</a>, Previous: <a href="Types-In-Guile.html#Types-In-Guile" accesskey="p" rel="prev">Types In Guile</a>, Up: <a href="Guile-API.html#Guile-API" accesskey="u" rel="up">Guile API</a> [<a href="index.html#SEC_Contents" title="Table of contents" rel="contents">Contents</a>][<a href="Concept-Index.html#Concept-Index" title="Index" rel="index">Index</a>]</p>
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</div>
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</body>
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</html>
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