201 lines
9.1 KiB
HTML
201 lines
9.1 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>Pretty Printing (Guile Reference Manual)</title>
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<meta name="description" content="Pretty Printing (Guile Reference Manual)">
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<meta name="keywords" content="Pretty Printing (Guile Reference Manual)">
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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=".texi2any-real">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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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="Guile-Modules.html" rel="up" title="Guile Modules">
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<link href="Formatted-Output.html" rel="next" title="Formatted Output">
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<link href="Readline-Support.html" rel="prev" title="Readline Support">
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<style type="text/css">
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<!--
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a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
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div.example {margin-left: 3.2em}
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span:hover a.copiable-link {visibility: visible}
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strong.def-name {font-family: monospace; font-weight: bold; font-size: larger}
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-->
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</style>
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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="section-level-extent" id="Pretty-Printing">
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<div class="nav-panel">
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<p>
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Next: <a href="Formatted-Output.html" accesskey="n" rel="next">Formatted Output</a>, Previous: <a href="Readline-Support.html" accesskey="p" rel="prev">Readline Support</a>, Up: <a href="Guile-Modules.html" accesskey="u" rel="up">Guile Modules</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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<h3 class="section" id="Pretty-Printing-1"><span>7.10 Pretty Printing<a class="copiable-link" href="#Pretty-Printing-1"> ¶</a></span></h3>
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<a class="index-entry-id" id="index-pretty-printing"></a>
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<p>The module <code class="code">(ice-9 pretty-print)</code> provides the procedure
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<code class="code">pretty-print</code>, which provides nicely formatted output of Scheme
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objects. This is especially useful for deeply nested or complex data
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structures, such as lists and vectors.
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</p>
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<p>The module is loaded by entering the following:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(use-modules (ice-9 pretty-print))
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</pre></div>
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<p>This makes the procedure <code class="code">pretty-print</code> available. As an example
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how <code class="code">pretty-print</code> will format the output, see the following:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(pretty-print '(define (foo) (lambda (x)
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(cond ((zero? x) #t) ((negative? x) -x) (else
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(if (= x 1) 2 (* x x x)))))))
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-|
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(define (foo)
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(lambda (x)
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(cond ((zero? x) #t)
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((negative? x) -x)
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(else (if (= x 1) 2 (* x x x))))))
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</pre></div>
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<dl class="first-deffn">
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<dt class="deffn" id="index-pretty_002dprint-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">pretty-print</strong> <var class="def-var-arguments">obj [port] [keyword-options]</var><a class="copiable-link" href="#index-pretty_002dprint-1"> ¶</a></span></dt>
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<dd><p>Print the textual representation of the Scheme object <var class="var">obj</var> to
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<var class="var">port</var>. <var class="var">port</var> defaults to the current output port, if not
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given.
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</p>
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<p>The further <var class="var">keyword-options</var> are keywords and parameters as
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follows,
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</p>
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<dl class="table">
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<dt><code class="code">#:display?</code> <var class="var">flag</var></dt>
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<dd><p>If <var class="var">flag</var> is true then print using <code class="code">display</code>. The default is
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<code class="code">#f</code> which means use <code class="code">write</code> style. See <a class="xref" href="Scheme-Write.html">Writing Scheme Values</a>.
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</p>
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</dd>
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<dt><code class="code">#:per-line-prefix</code> <var class="var">string</var></dt>
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<dd><p>Print the given <var class="var">string</var> as a prefix on each line. The default is
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no prefix.
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</p>
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</dd>
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<dt><code class="code">#:width</code> <var class="var">columns</var></dt>
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<dd><p>Print within the given <var class="var">columns</var>. The default is 79.
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</p>
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</dd>
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<dt><code class="code">#:max-expr-width</code> <var class="var">columns</var></dt>
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<dd><p>The maximum width of an expression. The default is 50.
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</p></dd>
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</dl>
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</dd></dl>
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<a class="index-entry-id" id="index-truncated-printing"></a>
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<p>Also exported by the <code class="code">(ice-9 pretty-print)</code> module is
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<code class="code">truncated-print</code>, a procedure to print Scheme datums, truncating
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the output to a certain number of characters. This is useful when you
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need to present an arbitrary datum to the user, but you only have one
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line in which to do so.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define exp '(a b #(c d e) f . g))
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(truncated-print exp #:width 10) (newline)
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-| (a b . #)
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(truncated-print exp #:width 15) (newline)
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-| (a b # f . g)
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(truncated-print exp #:width 18) (newline)
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-| (a b #(c ...) . #)
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(truncated-print exp #:width 20) (newline)
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-| (a b #(c d e) f . g)
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(truncated-print "The quick brown fox" #:width 20) (newline)
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-| "The quick brown..."
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(truncated-print (current-module) #:width 20) (newline)
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-| #<directory (gui...>
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</pre></div>
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<p><code class="code">truncated-print</code> will not output a trailing newline. If an expression does
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not fit in the given width, it will be truncated – possibly
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ellipsized<a class="footnote" id="DOCF26" href="#FOOT26"><sup>26</sup></a>, or in the worst case, displayed as <code class="code">#</code>.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-truncated_002dprint"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">truncated-print</strong> <var class="def-var-arguments">obj [port] [keyword-options]</var><a class="copiable-link" href="#index-truncated_002dprint"> ¶</a></span></dt>
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<dd><p>Print <var class="var">obj</var>, truncating the output, if necessary, to make it fit
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into <var class="var">width</var> characters. By default, <var class="var">obj</var> will be printed using
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<code class="code">write</code>, though that behavior can be overridden via the
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<var class="var">display?</var> keyword argument.
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</p>
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<p>The default behavior is to print depth-first, meaning that the entire
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remaining width will be available to each sub-expression of <var class="var">obj</var> –
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e.g., if <var class="var">obj</var> is a vector, each member of <var class="var">obj</var>. One can attempt to
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“ration” the available width, trying to allocate it equally to each
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sub-expression, via the <var class="var">breadth-first?</var> keyword argument.
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</p>
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<p>The further <var class="var">keyword-options</var> are keywords and parameters as
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follows,
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</p>
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<dl class="table">
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<dt><code class="code">#:display?</code> <var class="var">flag</var></dt>
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<dd><p>If <var class="var">flag</var> is true then print using <code class="code">display</code>. The default is
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<code class="code">#f</code> which means use <code class="code">write</code> style. see <a class="pxref" href="Scheme-Write.html">Writing Scheme Values</a>.
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</p>
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</dd>
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<dt><code class="code">#:width</code> <var class="var">columns</var></dt>
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<dd><p>Print within the given <var class="var">columns</var>. The default is 79.
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</p>
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</dd>
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<dt><code class="code">#:breadth-first?</code> <var class="var">flag</var></dt>
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<dd><p>If <var class="var">flag</var> is true, then allocate the available width breadth-first
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among elements of a compound data structure (list, vector, pair,
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etc.). The default is <code class="code">#f</code> which means that any element is
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allowed to consume all of the available width.
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</p></dd>
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</dl>
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</dd></dl>
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</div>
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<div class="footnotes-segment">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h5 class="footnote-body-heading"><a id="FOOT26" href="#DOCF26">(26)</a></h5>
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<p>On Unicode-capable ports, the ellipsis is represented by
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character ‘HORIZONTAL ELLIPSIS’ (U+2026), otherwise it is represented by three
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dots.</p>
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</div>
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<hr>
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<div class="nav-panel">
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<p>
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Next: <a href="Formatted-Output.html">Formatted Output</a>, Previous: <a href="Readline-Support.html">Readline Support</a>, Up: <a href="Guile-Modules.html">Guile Modules</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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</body>
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</html>
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