93 lines
4.2 KiB
HTML
93 lines
4.2 KiB
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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>The SCM Type in Guile (Guile Reference Manual)</title>
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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="Data-Representation.html" rel="up" title="Data Representation">
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<link href="Conservative-GC.html" rel="prev" title="Conservative GC">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="The-SCM-Type-in-Guile">
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<div class="nav-panel">
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<p>
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Previous: <a href="Conservative-GC.html" accesskey="p" rel="prev">Conservative Garbage Collection</a>, Up: <a href="Data-Representation.html" accesskey="u" rel="up">Data Representation</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="The-SCM-Type-in-Guile-1"><span>9.2.5 The SCM Type in Guile<a class="copiable-link" href="#The-SCM-Type-in-Guile-1"> ¶</a></span></h4>
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<p>Guile classifies Scheme objects into two kinds: those that fit entirely
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within an <code class="code">SCM</code>, and those that require heap storage.
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</p>
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<p>The former class are called <em class="dfn">immediates</em>. The class of immediates
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includes small integers, characters, boolean values, the empty list, the
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mysterious end-of-file object, and some others.
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</p>
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<p>The remaining types are called, not surprisingly, <em class="dfn">non-immediates</em>.
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They include pairs, procedures, strings, vectors, and all other data
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types in Guile. For non-immediates, the <code class="code">SCM</code> word contains a
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pointer to data on the heap, with further information about the object
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in question is stored in that data.
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</p>
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<p>This section describes how the <code class="code">SCM</code> type is actually represented
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and used at the C level. Interested readers should see
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<code class="code">libguile/scm.h</code> for an exposition of how Guile stores type
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information.
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</p>
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<p>In fact, there are two basic C data types to represent objects in
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Guile: <code class="code">SCM</code> and <code class="code">scm_t_bits</code>.
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</p>
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<ul class="mini-toc">
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<li><a href="Relationship-Between-SCM-and-scm_005ft_005fbits.html" accesskey="1">Relationship Between <code class="code">SCM</code> and <code class="code">scm_t_bits</code></a></li>
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<li><a href="Immediate-Objects.html" accesskey="2">Immediate Objects</a></li>
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<li><a href="Non_002dImmediate-Objects.html" accesskey="3">Non-Immediate Objects</a></li>
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<li><a href="Allocating-Heap-Objects.html" accesskey="4">Allocating Heap Objects</a></li>
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<li><a href="Heap-Object-Type-Information.html" accesskey="5">Heap Object Type Information</a></li>
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<li><a href="Accessing-Heap-Object-Fields.html" accesskey="6">Accessing Heap Object Fields</a></li>
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</ul>
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</div>
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</body>
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</html>
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