127 lines
6.3 KiB
HTML
127 lines
6.3 KiB
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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>SRFI-17 (Guile Reference Manual)</title>
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<meta name="description" content="SRFI-17 (Guile Reference Manual)">
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<meta name="keywords" content="SRFI-17 (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="SRFI-Support.html" rel="up" title="SRFI Support">
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<link href="SRFI_002d18.html" rel="next" title="SRFI-18">
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<link href="SRFI_002d16.html" rel="prev" title="SRFI-16">
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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="SRFI_002d17">
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<div class="nav-panel">
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<p>
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Next: <a href="SRFI_002d18.html" accesskey="n" rel="next">SRFI-18 - Multithreading support</a>, Previous: <a href="SRFI_002d16.html" accesskey="p" rel="prev">SRFI-16 - case-lambda</a>, Up: <a href="SRFI-Support.html" accesskey="u" rel="up">SRFI Support 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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<h4 class="subsection" id="SRFI_002d17-_002d-Generalized-set_0021"><span>7.5.14 SRFI-17 - Generalized set!<a class="copiable-link" href="#SRFI_002d17-_002d-Generalized-set_0021"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-SRFI_002d17"></a>
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<p>This SRFI implements a generalized <code class="code">set!</code>, allowing some
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“referencing” functions to be used as the target location of a
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<code class="code">set!</code>. This feature is available from
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</p>
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<div class="example">
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<pre class="example-preformatted">(use-modules (srfi srfi-17))
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</pre></div>
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<p>For example <code class="code">vector-ref</code> is extended so that
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</p>
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<div class="example">
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<pre class="example-preformatted">(set! (vector-ref vec idx) new-value)
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</pre></div>
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<p>is equivalent to
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</p>
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<div class="example">
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<pre class="example-preformatted">(vector-set! vec idx new-value)
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</pre></div>
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<p>The idea is that a <code class="code">vector-ref</code> expression identifies a location,
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which may be either fetched or stored. The same form is used for the
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location in both cases, encouraging visual clarity. This is similar
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to the idea of an “lvalue” in C.
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</p>
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<p>The mechanism for this kind of <code class="code">set!</code> is in the Guile core
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(see <a class="pxref" href="Procedures-with-Setters.html">Procedures with Setters</a>). This module adds definitions of
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the following functions as procedures with setters, allowing them to
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be targets of a <code class="code">set!</code>,
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</p>
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<blockquote class="quotation">
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<p><code class="code">car</code>, <code class="code">cdr</code>, <code class="code">caar</code>, <code class="code">cadr</code>,
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<code class="code">cdar</code>, <code class="code">cddr</code>, <code class="code">caaar</code>, <code class="code">caadr</code>,
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<code class="code">cadar</code>, <code class="code">caddr</code>, <code class="code">cdaar</code>, <code class="code">cdadr</code>,
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<code class="code">cddar</code>, <code class="code">cdddr</code>, <code class="code">caaaar</code>, <code class="code">caaadr</code>,
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<code class="code">caadar</code>, <code class="code">caaddr</code>, <code class="code">cadaar</code>, <code class="code">cadadr</code>,
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<code class="code">caddar</code>, <code class="code">cadddr</code>, <code class="code">cdaaar</code>, <code class="code">cdaadr</code>,
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<code class="code">cdadar</code>, <code class="code">cdaddr</code>, <code class="code">cddaar</code>, <code class="code">cddadr</code>,
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<code class="code">cdddar</code>, <code class="code">cddddr</code>
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</p>
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<p><code class="code">string-ref</code>, <code class="code">vector-ref</code>
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</p></blockquote>
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<p>The SRFI specifies <code class="code">setter</code> (see <a class="pxref" href="Procedures-with-Setters.html">Procedures with Setters</a>) as
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a procedure with setter, allowing the setter for a procedure to be
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changed, eg. <code class="code">(set! (setter foo) my-new-setter-handler)</code>.
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Currently Guile does not implement this, a setter can only be
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specified on creation (<code class="code">getter-with-setter</code> below).
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</p>
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<dl class="first-deffn first-defun-alias-first-deffn">
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<dt class="deffn defun-alias-deffn" id="index-getter_002dwith_002dsetter"><span class="category-def">Function: </span><span><strong class="def-name">getter-with-setter</strong><a class="copiable-link" href="#index-getter_002dwith_002dsetter"> ¶</a></span></dt>
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<dd><p>The same as the Guile core <code class="code">make-procedure-with-setter</code>
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(see <a class="pxref" href="Procedures-with-Setters.html">Procedures with Setters</a>).
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</p></dd></dl>
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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="SRFI_002d18.html">SRFI-18 - Multithreading support</a>, Previous: <a href="SRFI_002d16.html">SRFI-16 - case-lambda</a>, Up: <a href="SRFI-Support.html">SRFI Support 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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