116 lines
5.8 KiB
HTML
116 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>Environments (Guile Reference Manual)</title>
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<meta name="description" content="Environments (Guile Reference Manual)">
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<meta name="keywords" content="Environments (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="Modules.html" rel="up" title="Modules">
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<link href="provide-and-require.html" rel="prev" title="provide and require">
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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="Environments">
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<div class="nav-panel">
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<p>
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Previous: <a href="provide-and-require.html" accesskey="p" rel="prev">provide and require</a>, Up: <a href="Modules.html" accesskey="u" rel="up">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="Environments-1"><span>6.18.12 Environments<a class="copiable-link" href="#Environments-1"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-environment-1"></a>
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<p>Scheme, as defined in R5RS, does <em class="emph">not</em> have a full module system.
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However it does define the concept of a top-level <em class="dfn">environment</em>.
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Such an environment maps identifiers (symbols) to Scheme objects such
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as procedures and lists: <a class="ref" href="About-Closure.html">The Concept of Closure</a>. In other words, it
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implements a set of <em class="dfn">bindings</em>.
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</p>
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<p>Environments in R5RS can be passed as the second argument to
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<code class="code">eval</code> (see <a class="pxref" href="Fly-Evaluation.html">Procedures for On the Fly Evaluation</a>). Three procedures are defined to
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return environments: <code class="code">scheme-report-environment</code>,
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<code class="code">null-environment</code> and <code class="code">interaction-environment</code> (see <a class="pxref" href="Fly-Evaluation.html">Procedures for On the Fly Evaluation</a>).
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</p>
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<p>In addition, in Guile any module can be used as an R5RS environment,
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i.e., passed as the second argument to <code class="code">eval</code>.
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</p>
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<p>Note: the following two procedures are available only when the
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<code class="code">(ice-9 r5rs)</code> module is loaded:
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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 r5rs))
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</pre></div>
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<dl class="first-deffn">
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<dt class="deffn" id="index-scheme_002dreport_002denvironment"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">scheme-report-environment</strong> <var class="def-var-arguments">version</var><a class="copiable-link" href="#index-scheme_002dreport_002denvironment"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-null_002denvironment"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">null-environment</strong> <var class="def-var-arguments">version</var><a class="copiable-link" href="#index-null_002denvironment"> ¶</a></span></dt>
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<dd><p><var class="var">version</var> must be the exact integer ‘5’, corresponding to revision
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5 of the Scheme report (the Revised^5 Report on Scheme).
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<code class="code">scheme-report-environment</code> returns a specifier for an
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environment that is empty except for all bindings defined in the
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report that are either required or both optional and supported by the
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implementation. <code class="code">null-environment</code> returns a specifier for an
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environment that is empty except for the (syntactic) bindings for all
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syntactic keywords defined in the report that are either required or
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both optional and supported by the implementation.
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</p>
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<p>Currently Guile does not support values of <var class="var">version</var> for other
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revisions of the report.
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</p>
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<p>The effect of assigning (through the use of <code class="code">eval</code>) a variable
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bound in a <code class="code">scheme-report-environment</code> (for example <code class="code">car</code>)
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is unspecified. Currently the environments specified by
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<code class="code">scheme-report-environment</code> are not immutable in Guile.
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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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Previous: <a href="provide-and-require.html">provide and require</a>, Up: <a href="Modules.html">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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