95 lines
3.7 KiB
HTML
95 lines
3.7 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>SRFI-31 (Guile Reference Manual)</title>
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<meta name="description" content="SRFI-31 (Guile Reference Manual)">
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<meta name="keywords" content="SRFI-31 (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_002d34.html" rel="next" title="SRFI-34">
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<link href="SRFI_002d30.html" rel="prev" title="SRFI-30">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="SRFI_002d31">
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<div class="nav-panel">
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<p>
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Next: <a href="SRFI_002d34.html" accesskey="n" rel="next">SRFI-34 - Exception handling for programs</a>, Previous: <a href="SRFI_002d30.html" accesskey="p" rel="prev">SRFI-30 - Nested Multi-line Comments</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_002d31-_002d-A-special-form-_0060rec_0027-for-recursive-evaluation"><span>7.5.22 SRFI-31 - A special form ‘rec’ for recursive evaluation<a class="copiable-link" href="#SRFI_002d31-_002d-A-special-form-_0060rec_0027-for-recursive-evaluation"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-SRFI_002d31"></a>
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<a class="index-entry-id" id="index-recursive-expression"></a>
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<a class="index-entry-id" id="index-rec"></a>
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<p>SRFI-31 defines a special form that can be used to create
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self-referential expressions more conveniently. The syntax is as
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follows:
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</p>
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<div class="example">
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<div class="group"><pre class="example-preformatted"><rec expression> --> (rec <variable> <expression>)
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<rec expression> --> (rec (<variable>+) <body>)
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</pre></div></div>
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<p>The first syntax can be used to create self-referential expressions,
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for example:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> guile> (define tmp (rec ones (cons 1 (delay ones))))
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</pre></div>
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<p>The second syntax can be used to create anonymous recursive functions:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted"> guile> (define tmp (rec (display-n item n)
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(if (positive? n)
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(begin (display n) (display-n (- n 1))))))
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guile> (tmp 42 3)
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424242
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guile>
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</pre></div>
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</div>
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</body>
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</html>
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