161 lines
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HTML
161 lines
11 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>Structure Basics (Guile Reference Manual)</title>
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<meta name="description" content="Structure Basics (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="Structures.html" rel="up" title="Structures">
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</head>
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<body lang="en">
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<div class="subsubsection-level-extent" id="Structure-Basics">
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<div class="nav-panel">
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<p>
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Next: <a href="Vtable-Contents.html" accesskey="n" rel="next">Vtable Contents</a>, Previous: <a href="Vtables.html" accesskey="p" rel="prev">Vtables</a>, Up: <a href="Structures.html" accesskey="u" rel="up">Structures</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="Structure-Basics-1"><span>6.6.18.2 Structure Basics<a class="copiable-link" href="#Structure-Basics-1"> ¶</a></span></h4>
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<p>This section describes the basic procedures for working with structures.
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<code class="code">make-struct/no-tail</code> creates a structure, and <code class="code">struct-ref</code>
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and <code class="code">struct-set!</code> access its fields.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002dstruct_002fno_002dtail"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-struct/no-tail</strong> <var class="def-var-arguments">vtable init …</var><a class="copiable-link" href="#index-make_002dstruct_002fno_002dtail"> ¶</a></span></dt>
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<dd><p>Create a new structure, with layout per the given <var class="var">vtable</var>
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(see <a class="pxref" href="Vtables.html">Vtables</a>).
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</p>
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<p>The optional <var class="var">init</var>… arguments are initial values for the
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fields of the structure. This is the only way to
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put values in read-only fields. If there are fewer <var class="var">init</var>
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arguments than fields then the defaults are <code class="code">#f</code> for a Scheme
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field (type <code class="code">p</code>) or 0 for an unboxed field (type <code class="code">u</code>).
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</p>
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<p>The name is a bit strange, we admit. The reason for it is that Guile
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used to have a <code class="code">make-struct</code> that took an additional argument;
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while we deprecate that old interface, <code class="code">make-struct/no-tail</code> is the
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new name for this functionality.
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</p>
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<p>For example,
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</p>
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<div class="example">
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<pre class="example-preformatted">(define v (make-vtable "pwpwpw"))
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(define s (make-struct/no-tail v 123 "abc" 456))
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(struct-ref s 0) ⇒ 123
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(struct-ref s 1) ⇒ "abc"
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</pre></div>
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</dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fmake_005fstruct"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_make_struct</strong> <code class="def-code-arguments">(SCM vtable, SCM tail_size, SCM init_list)</code><a class="copiable-link" href="#index-scm_005fmake_005fstruct"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fc_005fmake_005fstruct"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_c_make_struct</strong> <code class="def-code-arguments">(SCM vtable, SCM tail_size, SCM init, ...)</code><a class="copiable-link" href="#index-scm_005fc_005fmake_005fstruct"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-scm_005fc_005fmake_005fstructv"><span class="category-def">C Function: </span><span><code class="def-type">SCM</code> <strong class="def-name">scm_c_make_structv</strong> <code class="def-code-arguments">(SCM vtable, SCM tail_size, size_t n_inits, scm_t_bits init[])</code><a class="copiable-link" href="#index-scm_005fc_005fmake_005fstructv"> ¶</a></span></dt>
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<dd><p>There are a few ways to make structures from C. <code class="code">scm_make_struct</code>
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takes a list, <code class="code">scm_c_make_struct</code> takes variable arguments
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terminated with SCM_UNDEFINED, and <code class="code">scm_c_make_structv</code> takes a
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packed array.
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</p>
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<p>For all of these, <var class="var">tail_size</var> should be zero (as a SCM value).
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-struct_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">struct?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-struct_003f"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstruct_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_struct_p</strong> <var class="def-var-arguments">(obj)</var><a class="copiable-link" href="#index-scm_005fstruct_005fp"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a structure, or <code class="code">#f</code> if not.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-struct_002dref"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">struct-ref</strong> <var class="def-var-arguments">struct n</var><a class="copiable-link" href="#index-struct_002dref"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstruct_005fref"><span class="category-def">C Function: </span><span><strong class="def-name">scm_struct_ref</strong> <var class="def-var-arguments">(struct, n)</var><a class="copiable-link" href="#index-scm_005fstruct_005fref"> ¶</a></span></dt>
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<dd><p>Return the contents of field number <var class="var">n</var> in <var class="var">struct</var>. The
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first field is number 0.
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</p>
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<p>An error is thrown if <var class="var">n</var> is out of range.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-struct_002dset_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">struct-set!</strong> <var class="def-var-arguments">struct n value</var><a class="copiable-link" href="#index-struct_002dset_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstruct_005fset_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_struct_set_x</strong> <var class="def-var-arguments">(struct, n, value)</var><a class="copiable-link" href="#index-scm_005fstruct_005fset_005fx"> ¶</a></span></dt>
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<dd><p>Set field number <var class="var">n</var> in <var class="var">struct</var> to <var class="var">value</var>. The first
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field is number 0.
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</p>
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<p>An error is thrown if <var class="var">n</var> is out of range, or if the field cannot
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be written because it’s <code class="code">r</code> read-only.
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</p></dd></dl>
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<p>Unboxed fields (those with type <code class="code">u</code>) need to be accessed with
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special procedures.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-struct_002dref_002funboxed"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">struct-ref/unboxed</strong> <var class="def-var-arguments">struct n</var><a class="copiable-link" href="#index-struct_002dref_002funboxed"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-struct_002dset_0021_002funboxed"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">struct-set!/unboxed</strong> <var class="def-var-arguments">struct n value</var><a class="copiable-link" href="#index-struct_002dset_0021_002funboxed"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstruct_005fref_005funboxed"><span class="category-def">C Function: </span><span><strong class="def-name">scm_struct_ref_unboxed</strong> <var class="def-var-arguments">(struct, n)</var><a class="copiable-link" href="#index-scm_005fstruct_005fref_005funboxed"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstruct_005fset_005fx_005funboxed"><span class="category-def">C Function: </span><span><strong class="def-name">scm_struct_set_x_unboxed</strong> <var class="def-var-arguments">(struct, n, value)</var><a class="copiable-link" href="#index-scm_005fstruct_005fset_005fx_005funboxed"> ¶</a></span></dt>
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<dd><p>Like <code class="code">struct-ref</code> and <code class="code">struct-set!</code>, except that these may
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only be used on unboxed fields. <code class="code">struct-ref/unboxed</code> will always
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return a positive integer. Likewise, <code class="code">struct-set!/unboxed</code> takes
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an unsigned integer as the <var class="var">value</var> argument, and will signal an
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error otherwise.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-struct_002dvtable"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">struct-vtable</strong> <var class="def-var-arguments">struct</var><a class="copiable-link" href="#index-struct_002dvtable"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstruct_005fvtable"><span class="category-def">C Function: </span><span><strong class="def-name">scm_struct_vtable</strong> <var class="def-var-arguments">(struct)</var><a class="copiable-link" href="#index-scm_005fstruct_005fvtable"> ¶</a></span></dt>
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<dd><p>Return the vtable that describes <var class="var">struct</var>.
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</p>
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<p>The vtable is effectively the type of the structure. See <a class="ref" href="Vtable-Contents.html">Vtable Contents</a>, for more on vtables.
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</p></dd></dl>
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</div>
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<hr>
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<p>
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Next: <a href="Vtable-Contents.html">Vtable Contents</a>, Previous: <a href="Vtables.html">Vtables</a>, Up: <a href="Structures.html">Structures</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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