118 lines
5.7 KiB
HTML
118 lines
5.7 KiB
HTML
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Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Available Functionality (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="Programming-Options.html" rel="up" title="Programming Options">
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<link href="Basic-Constraints.html" rel="next" title="Basic Constraints">
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<div class="subsubsection-level-extent" id="Available-Functionality">
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<p>
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Next: <a href="Basic-Constraints.html" accesskey="n" rel="next">Functional and Performance Constraints</a>, Up: <a href="Programming-Options.html" accesskey="u" rel="up">A Choice of Programming Options</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="subsubsection" id="What-Functionality-is-Already-Available_003f"><span>5.7.4.1 What Functionality is Already Available?<a class="copiable-link" href="#What-Functionality-is-Already-Available_003f"> ¶</a></span></h4>
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<p>Suppose, for the sake of argument, that you would prefer to write your
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whole application in Scheme. Then the API available to you consists of:
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</p>
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<ul class="itemize mark-bullet">
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<li>standard Scheme
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</li><li>plus the extensions to standard Scheme provided by
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Guile in its core distribution
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</li><li>plus any additional functionality that you or others have packaged so
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that it can be loaded as a Guile Scheme module.
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</li></ul>
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<p>A module in the last category can either be a pure Scheme module — in
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other words a collection of utility procedures coded in Scheme — or a
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module that provides a Scheme interface to an extension library coded in
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C — in other words a nice package where someone else has done the work
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of wrapping up some useful C code for you. The set of available modules
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is growing quickly and already includes such useful examples as
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<code class="code">(gtk gtk)</code>, which makes Gtk+ drawing functions available in
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Scheme, and <code class="code">(database postgres)</code>, which provides SQL access to a
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Postgres database.
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</p>
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<p>Given the growing collection of pre-existing modules, it is quite
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feasible that your application could be implemented by combining a
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selection of these modules together with new application code written in
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Scheme.
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</p>
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<p>If this approach is not enough, because the functionality that your
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application needs is not already available in this form, and it is
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impossible to write the new functionality in Scheme, you will need to
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write some C code. If the required function is already available in C
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(e.g. in a library), all you need is a little glue to connect it to the
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world of Guile. If not, you need both to write the basic code and to
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plumb it into Guile.
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</p>
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<p>In either case, two general considerations are important. Firstly, what
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is the interface by which the functionality is presented to the Scheme
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world? Does the interface consist only of function calls (for example,
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a simple drawing interface), or does it need to include <em class="dfn">objects</em> of
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some kind that can be passed between C and Scheme and manipulated by
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both worlds. Secondly, how does the lifetime and memory management of
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objects in the C code relate to the garbage collection governed approach
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of Scheme objects? In the case where the basic C code is not already
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written, most of the difficulties of memory management can be avoided by
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using Guile’s C interface features from the start.
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</p>
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<p>For the full documentation on writing C code for Guile and connecting
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existing C code to the Guile world, see <a class="ref" href="Defining-New-Foreign-Object-Types.html">Defining New Foreign Object Types</a>, <a class="ref" href="Primitive-Procedures.html">Primitive Procedures</a>, and <a class="ref" href="Foreign-Function-Interface.html">Foreign Function Interface</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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Next: <a href="Basic-Constraints.html">Functional and Performance Constraints</a>, Up: <a href="Programming-Options.html">A Choice of Programming Options</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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