140 lines
7.5 KiB
HTML
140 lines
7.5 KiB
HTML
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<!DOCTYPE html>
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<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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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>Foreign Functions (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="Foreign-Function-Interface.html" rel="up" title="Foreign Function Interface">
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<link href="Void-Pointers-and-Byte-Access.html" rel="next" title="Void Pointers and Byte Access">
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<link href="Foreign-Types.html" rel="prev" title="Foreign Types">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Foreign-Functions">
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<div class="nav-panel">
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<p>
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Next: <a href="Void-Pointers-and-Byte-Access.html" accesskey="n" rel="next">Void Pointers and Byte Access</a>, Previous: <a href="Foreign-Types.html" accesskey="p" rel="prev">Foreign Types</a>, Up: <a href="Foreign-Function-Interface.html" accesskey="u" rel="up">Foreign Function Interface</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="Foreign-Functions-1"><span>6.19.5 Foreign Functions<a class="copiable-link" href="#Foreign-Functions-1"> ¶</a></span></h4>
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<p>The most natural thing to do with a dynamic library is to grovel around
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in it for a function pointer: a <em class="dfn">foreign function</em>. Load the
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<code class="code">(system foreign)</code> module to use these Scheme interfaces.
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</p>
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<div class="example">
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<pre class="example-preformatted">(use-modules (system foreign))
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</pre></div>
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<dl class="first-deffn">
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<dt class="deffn" id="index-pointer_002d_003eprocedure"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">pointer->procedure</strong> <var class="def-var-arguments">return_type func_ptr arg_types [#:return-errno?=#f]</var><a class="copiable-link" href="#index-pointer_002d_003eprocedure"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fpointer_005fto_005fprocedure"><span class="category-def">C Function: </span><span><strong class="def-name">scm_pointer_to_procedure</strong> <var class="def-var-arguments">(return_type, func_ptr, arg_types)</var><a class="copiable-link" href="#index-scm_005fpointer_005fto_005fprocedure"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fpointer_005fto_005fprocedure_005fwith_005ferrno"><span class="category-def">C Function: </span><span><strong class="def-name">scm_pointer_to_procedure_with_errno</strong> <var class="def-var-arguments">(return_type, func_ptr, arg_types)</var><a class="copiable-link" href="#index-scm_005fpointer_005fto_005fprocedure_005fwith_005ferrno"> ¶</a></span></dt>
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<dd>
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<p>Make a foreign function.
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</p>
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<p>Given the foreign void pointer <var class="var">func_ptr</var>, its argument and
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return types <var class="var">arg_types</var> and <var class="var">return_type</var>, return a
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procedure that will pass arguments to the foreign function
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and return appropriate values.
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</p>
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<p><var class="var">arg_types</var> should be a list of foreign types.
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<code class="code">return_type</code> should be a foreign type. See <a class="xref" href="Foreign-Types.html">Foreign Types</a>, for
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more information on foreign types.
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</p>
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<p>If <var class="var">return-errno?</var> is true, or when calling
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<code class="code">scm_pointer_to_procedure_with_errno</code>, the returned procedure will
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return two values, with <code class="code">errno</code> as the second value.
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</p></dd></dl>
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<p>Finally, in <code class="code">(system foreign-library)</code> there is a convenient
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wrapper function, joining together <code class="code">foreign-library-pointer</code> and
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<code class="code">procedure->pointer</code>:
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-foreign_002dlibrary_002dfunction"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">foreign-library-function</strong> <var class="def-var-arguments">lib name [#:return-type=void] [#:arg-types=’()] [#:return-errno?=#f]</var><a class="copiable-link" href="#index-foreign_002dlibrary_002dfunction"> ¶</a></span></dt>
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<dd><p>Load the address of <var class="var">name</var> from <var class="var">lib</var>, and treat it as a
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function taking arguments <var class="var">arg-types</var> and returning
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<var class="var">return-type</var>, optionally also with errno.
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</p>
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<p>An invocation of <code class="code">foreign-library-function</code> is entirely equivalent
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to:
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</p><div class="example">
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<pre class="example-preformatted">(pointer->procedure <var class="var">return-type</var>
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(foreign-library-pointer <var class="var">lib</var> <var class="var">name</var>)
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<var class="var">arg-types</var>
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#:return-errno? <var class="var">return-errno?</var>).
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</pre></div>
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</dd></dl>
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<p>Pulling all this together, here is a better definition of <code class="code">(math
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bessel)</code>:
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</p>
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<div class="example">
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<pre class="example-preformatted">(define-module (math bessel)
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#:use-module (system foreign)
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#:use-module (system foreign-library)
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#:export (j0))
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(define j0
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(foreign-library-function "libm" "j0"
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#:return-type double
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#:arg-types (list double)))
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</pre></div>
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<p>That’s it! No C at all.
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</p>
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<p>Before going on to more detailed examples, the next two sections discuss
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how to deal with data that is more complex than, say, <code class="code">int8</code>.
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See <a class="xref" href="More-Foreign-Functions.html">More Foreign Functions</a>, to continue with foreign function examples.
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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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Next: <a href="Void-Pointers-and-Byte-Access.html">Void Pointers and Byte Access</a>, Previous: <a href="Foreign-Types.html">Foreign Types</a>, Up: <a href="Foreign-Function-Interface.html">Foreign Function Interface</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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