139 lines
5.8 KiB
HTML
139 lines
5.8 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>Symbol Read Syntax (Guile Reference Manual)</title>
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<meta name="description" content="Symbol Read Syntax (Guile Reference Manual)">
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<meta name="keywords" content="Symbol Read Syntax (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="Symbols.html" rel="up" title="Symbols">
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<link href="Symbol-Uninterned.html" rel="next" title="Symbol Uninterned">
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<link href="Symbol-Primitives.html" rel="prev" title="Symbol Primitives">
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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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</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="subsubsection-level-extent" id="Symbol-Read-Syntax">
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<div class="nav-panel">
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<p>
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Next: <a href="Symbol-Uninterned.html" accesskey="n" rel="next">Uninterned Symbols</a>, Previous: <a href="Symbol-Primitives.html" accesskey="p" rel="prev">Operations Related to Symbols</a>, Up: <a href="Symbols.html" accesskey="u" rel="up">Symbols</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="subsubsection" id="Extended-Read-Syntax-for-Symbols"><span>6.6.6.5 Extended Read Syntax for Symbols<a class="copiable-link" href="#Extended-Read-Syntax-for-Symbols"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-r7rs_002dsymbols"></a>
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<p>The read syntax for a symbol is a sequence of letters, digits, and
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<em class="dfn">extended alphabetic characters</em>, beginning with a character that
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cannot begin a number. In addition, the special cases of <code class="code">+</code>,
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<code class="code">-</code>, and <code class="code">...</code> are read as symbols even though numbers can
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begin with <code class="code">+</code>, <code class="code">-</code> or <code class="code">.</code>.
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</p>
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<p>Extended alphabetic characters may be used within identifiers as if
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they were letters. The set of extended alphabetic characters is:
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</p>
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<div class="example">
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<pre class="example-preformatted">! $ % & * + - . / : < = > ? @ ^ _ ~
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</pre></div>
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<p>In addition to the standard read syntax defined above (which is taken
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from R5RS (see <a data-manual="r5rs" href="../r5rs_html/Formal-syntax.html#Formal-syntax">Formal syntax</a> in <cite class="cite">The Revised^5 Report on
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Scheme</cite>)), Guile provides an extended symbol read syntax that allows the
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inclusion of unusual characters such as space characters, newlines and
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parentheses. If (for whatever reason) you need to write a symbol
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containing characters not mentioned above, you can do so as follows.
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</p>
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<ul class="itemize mark-bullet">
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<li>Begin the symbol with the characters <code class="code">#{</code>,
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</li><li>write the characters of the symbol and
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</li><li>finish the symbol with the characters <code class="code">}#</code>.
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</li></ul>
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<p>Here are a few examples of this form of read syntax. The first symbol
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needs to use extended syntax because it contains a space character, the
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second because it contains a line break, and the last because it looks
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like a number.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">#{foo bar}#
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#{what
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ever}#
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#{4242}#
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</pre></div>
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<p>Although Guile provides this extended read syntax for symbols,
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widespread usage of it is discouraged because it is not portable and not
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very readable.
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</p>
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<p>Alternatively, if you enable the <code class="code">r7rs-symbols</code> read option (see
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see <a class="pxref" href="Scheme-Read.html">Reading Scheme Code</a>), you can write arbitrary symbols using the same
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notation used for strings, except delimited by vertical bars instead of
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double quotes.
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</p>
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<div class="example">
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<pre class="example-preformatted">|foo bar|
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|\x3BB; is a greek lambda|
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|\| is a vertical bar|
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</pre></div>
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<p>Note that there’s also an <code class="code">r7rs-symbols</code> print option
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(see <a class="pxref" href="Scheme-Write.html">Writing Scheme Values</a>). To enable the use of this notation, evaluate
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one or both of the following expressions:
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</p>
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<div class="example">
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<pre class="example-preformatted">(read-enable 'r7rs-symbols)
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(print-enable 'r7rs-symbols)
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</pre></div>
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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="Symbol-Uninterned.html">Uninterned Symbols</a>, Previous: <a href="Symbol-Primitives.html">Operations Related to Symbols</a>, Up: <a href="Symbols.html">Symbols</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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