137 lines
6.3 KiB
HTML
137 lines
6.3 KiB
HTML
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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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>User Programming (Guile Reference Manual)</title>
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<meta name="description" content="User Programming (Guile Reference Manual)">
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<meta name="keywords" content="User Programming (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="Programming-Overview.html" rel="up" title="Programming Overview">
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<link href="Programming-Options.html" rel="prev" title="Programming Options">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="User-Programming">
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<div class="nav-panel">
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<p>
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Previous: <a href="Programming-Options.html" accesskey="p" rel="prev">A Choice of Programming Options</a>, Up: <a href="Programming-Overview.html" accesskey="u" rel="up">An Overview of Guile Programming</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="How-About-Application-Users_003f"><span>5.7.5 How About Application Users?<a class="copiable-link" href="#How-About-Application-Users_003f"> ¶</a></span></h4>
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<p>So far we have considered what Guile programming means for an
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application developer. But what if you are instead <em class="emph">using</em> an
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existing Guile-based application, and want to know what your
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options are for programming and extending this application?
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</p>
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<p>The answer to this question varies from one application to another,
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because the options available depend inevitably on whether the
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application developer has provided any hooks for you to hang your own
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code on and, if there are such hooks, what they allow you to
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do.<a class="footnote" id="DOCF7" href="#FOOT7"><sup>7</sup></a> For example…
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</p>
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<ul class="itemize mark-bullet">
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<li>If the application permits you to load and execute any Guile code, the
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world is your oyster. You can extend the application in any way that
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you choose.
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</li><li>A more cautious application might allow you to load and execute Guile
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code, but only in a <em class="dfn">safe</em> environment, where the interface
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available is restricted by the application from the standard Guile API.
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</li><li>Or a really fearful application might not provide a hook to really
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execute user code at all, but just use Scheme syntax as a convenient way
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for users to specify application data or configuration options.
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</li></ul>
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<p>In the last two cases, what you can do is, by definition, restricted by
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the application, and you should refer to the application’s own manual to
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find out your options.
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</p>
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<p>The most well known example of the first case is Emacs, with its
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extension language Emacs Lisp: as well as being a text editor, Emacs
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supports the loading and execution of arbitrary Emacs Lisp code. The
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result of such openness has been dramatic: Emacs now benefits from
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user-contributed Emacs Lisp libraries that extend the basic editing
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function to do everything from reading news to psychoanalysis and
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playing adventure games. The only limitation is that extensions are
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restricted to the functionality provided by Emacs’s built-in set of
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primitive operations. For example, you can interact and display data by
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manipulating the contents of an Emacs buffer, but you can’t pop-up and
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draw a window with a layout that is totally different to the Emacs
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standard.
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</p>
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<p>This situation with a Guile application that supports the loading of
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arbitrary user code is similar, except perhaps even more so, because
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Guile also supports the loading of extension libraries written in C.
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This last point enables user code to add new primitive operations to
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Guile, and so to bypass the limitation present in Emacs Lisp.
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</p>
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<p>At this point, the distinction between an application developer and an
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application user becomes rather blurred. Instead of seeing yourself as
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a user extending an application, you could equally well say that you are
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developing a new application of your own using some of the primitive
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functionality provided by the original application. As such, all the
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discussions of the preceding sections of this chapter are relevant to
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how you can proceed with developing your extension.
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</p>
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</div>
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<div class="footnotes-segment">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h5 class="footnote-body-heading"><a id="FOOT7" href="#DOCF7">(7)</a></h5>
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<p>Of course, in the world of free software, you always have
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the freedom to modify the application’s source code to your own
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requirements. Here we are concerned with the extension options that the
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application has provided for without your needing to modify its source
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code.</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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Previous: <a href="Programming-Options.html">A Choice of Programming Options</a>, Up: <a href="Programming-Overview.html">An Overview of Guile Programming</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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