130 lines
5.3 KiB
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130 lines
5.3 KiB
HTML
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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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<title>A Sample Guile Extension (Guile Reference Manual)</title>
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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="Linking-Guile-with-Libraries.html" rel="up" title="Linking Guile with Libraries">
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<body lang="en">
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<div class="subsection-level-extent" id="A-Sample-Guile-Extension">
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<div class="nav-panel">
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<p>
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Up: <a href="Linking-Guile-with-Libraries.html" accesskey="u" rel="up">Linking Guile with Libraries</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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<hr>
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<h4 class="subsection" id="A-Sample-Guile-Extension-1"><span>5.3.1 A Sample Guile Extension<a class="copiable-link" href="#A-Sample-Guile-Extension-1"> ¶</a></span></h4>
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<p>This section explains how to make the Bessel functions of the C library
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available to Scheme. First we need to write the appropriate glue code
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to convert the arguments and return values of the functions from Scheme
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to C and back. Additionally, we need a function that will add them to
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the set of Guile primitives. Because this is just an example, we will
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only implement this for the <code class="code">j0</code> function.
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</p>
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<p>Consider the following file <samp class="file">bessel.c</samp>.
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</p>
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<div class="example smallexample">
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<pre class="example-preformatted">#include <math.h>
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#include <libguile.h>
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SCM
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j0_wrapper (SCM x)
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{
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return scm_from_double (j0 (scm_to_double (x)));
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}
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void
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init_bessel ()
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{
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scm_c_define_gsubr ("j0", 1, 0, 0, j0_wrapper);
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}
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</pre></div>
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<p>This C source file needs to be compiled into a shared library. Here is
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how to do it on GNU/Linux:
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</p>
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<div class="example smallexample">
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<pre class="example-preformatted">gcc `pkg-config --cflags guile-3.0` \
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-shared -o libguile-bessel.so -fPIC bessel.c
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</pre></div>
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<p>For creating shared libraries portably, we recommend the use of GNU
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Libtool (see <a data-manual="libtool" href="https://www.gnu.org/software/libtool/manual/html_node/index.html#Top">Introduction</a> in <cite class="cite">GNU Libtool</cite>).
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</p>
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<p>A shared library can be loaded into a running Guile process with the
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function <code class="code">load-extension</code>. In addition to the name of the
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library to load, this function also expects the name of a function from
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that library that will be called to initialize it. For our example,
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we are going to call the function <code class="code">init_bessel</code> which will make
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<code class="code">j0_wrapper</code> available to Scheme programs with the name
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<code class="code">j0</code>. Note that we do not specify a filename extension such as
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<samp class="file">.so</samp> when invoking <code class="code">load-extension</code>. The right extension for
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the host platform will be provided automatically.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(load-extension "libguile-bessel" "init_bessel")
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(j0 2)
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⇒ 0.223890779141236
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</pre></div>
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<p>For this to work, <code class="code">load-extension</code> must be able to find
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<samp class="file">libguile-bessel</samp>, of course. It will look in the places that
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are usual for your operating system, and it will additionally look
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into the directories listed in the <code class="code">LTDL_LIBRARY_PATH</code>
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environment variable.
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</p>
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<p>To see how these Guile extensions via shared libraries relate to the
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module system, See <a class="xref" href="Putting-Extensions-into-Modules.html">Putting Extensions into Modules</a>.
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</p>
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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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Up: <a href="Linking-Guile-with-Libraries.html">Linking Guile with Libraries</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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