114 lines
5.2 KiB
HTML
114 lines
5.2 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>Block Comments (Guile Reference Manual)</title>
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<meta name="description" content="Block Comments (Guile Reference Manual)">
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<meta name="keywords" content="Block Comments (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="Scheme-Syntax.html" rel="up" title="Scheme Syntax">
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<link href="Case-Sensitivity.html" rel="next" title="Case Sensitivity">
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<link href="Comments.html" rel="prev" title="Comments">
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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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-->
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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="Block-Comments">
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<div class="nav-panel">
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<p>
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Next: <a href="Case-Sensitivity.html" accesskey="n" rel="next">Case Sensitivity</a>, Previous: <a href="Comments.html" accesskey="p" rel="prev">Comments</a>, Up: <a href="Scheme-Syntax.html" accesskey="u" rel="up">Scheme Syntax: Standard and Guile Extensions</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="Block-Comments-1"><span>6.16.1.3 Block Comments<a class="copiable-link" href="#Block-Comments-1"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-multiline-comments"></a>
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<a class="index-entry-id" id="index-block-comments"></a>
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<a class="index-entry-id" id="index-_0023_0021"></a>
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<a class="index-entry-id" id="index-_0021_0023"></a>
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<p>In addition to the standard line comments defined by R5RS, Guile has
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another comment type for multiline comments, called <em class="dfn">block
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comments</em>. This type of comment begins with the character sequence
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<code class="code">#!</code> and ends with the characters <code class="code">!#</code>.
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</p>
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<p>These comments are compatible with the block
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comments in the Scheme Shell <samp class="file">scsh</samp> (see <a class="pxref" href="The-Scheme-shell-_0028scsh_0029.html">The Scheme shell (scsh)</a>). The characters <code class="code">#!</code> were chosen because they are the
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magic characters used in shell scripts for indicating that the name of
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the program for executing the script follows on the same line.
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</p>
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<p>Thus a Guile script often starts like this.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">#! /usr/local/bin/guile -s
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!#
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</pre></div>
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<p>More details on Guile scripting can be found in the scripting section
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(see <a class="pxref" href="Guile-Scripting.html">Guile Scripting</a>).
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</p>
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<a class="index-entry-id" id="index-R6RS-block-comments"></a>
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<a class="index-entry-id" id="index-SRFI_002d30-block-comments"></a>
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<p>Similarly, Guile (starting from version 2.0) supports nested block
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comments as specified by R6RS and
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<a class="url" href="http://srfi.schemers.org/srfi-30/srfi-30.html">SRFI-30</a>:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(+ 1 #| this is a #| nested |# block comment |# 2)
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⇒ 3
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</pre></div>
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<p>For backward compatibility, this syntax can be overridden with
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<code class="code">read-hash-extend</code> (see <a class="pxref" href="Reader-Extensions.html"><code class="code">read-hash-extend</code></a>).
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</p>
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<p>There is one special case where the contents of a comment can actually
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affect the interpretation of code. When a character encoding
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declaration, such as <code class="code">coding: utf-8</code> appears in one of the first
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few lines of a source file, it indicates to Guile’s default reader
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that this source code file is not ASCII. For details see <a class="ref" href="Character-Encoding-of-Source-Files.html">Character Encoding of Source Files</a>.
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</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="Case-Sensitivity.html">Case Sensitivity</a>, Previous: <a href="Comments.html">Comments</a>, Up: <a href="Scheme-Syntax.html">Scheme Syntax: Standard and Guile Extensions</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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