114 lines
4.8 KiB
HTML
114 lines
4.8 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>Dia Objective (Guile Reference Manual)</title>
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<meta name="description" content="Dia Objective (Guile Reference Manual)">
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<meta name="keywords" content="Dia Objective (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="Extending-Dia.html" rel="up" title="Extending Dia">
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<link href="Dia-Steps.html" rel="next" title="Dia Steps">
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsubsection-level-extent" id="Dia-Objective">
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<div class="nav-panel">
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<p>
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Next: <a href="Dia-Steps.html" accesskey="n" rel="next">Four Steps Required to Add Guile</a>, Up: <a href="Extending-Dia.html" accesskey="u" rel="up">How One Might Extend Dia Using Guile</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="Deciding-Why-You-Want-to-Add-Guile"><span>5.7.1.1 Deciding Why You Want to Add Guile<a class="copiable-link" href="#Deciding-Why-You-Want-to-Add-Guile"> ¶</a></span></h4>
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<p>First off, you should understand why you want to add Guile to Dia at
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all, and that means forming a picture of what Dia does and how it does
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it. So, what are the constituents of the Dia application?
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</p>
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<ul class="itemize mark-bullet">
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<li>Most importantly, the <em class="dfn">application domain objects</em> — in other
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words, the concepts that differentiate Dia from another application such
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as a word processor or spreadsheet: shapes, templates, connectors,
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pages, plus the properties of all these things.
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</li><li>The code that manages the graphical face of the application, including
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the layout and display of the objects above.
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</li><li>The code that handles input events, which indicate that the application
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user is wanting to do something.
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</li></ul>
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<p>(In other words, a textbook example of the <em class="dfn">model - view -
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controller</em> paradigm.)
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</p>
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<p>Next question: how will Dia benefit once the Guile integration is
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complete? Several (positive!) answers are possible here, and the choice
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is obviously up to the application developers. Still, one answer is
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that the main benefit will be the ability to manipulate Dia’s
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application domain objects from Scheme.
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</p>
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<p>Suppose that Dia made a set of procedures available in Scheme,
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representing the most basic operations on objects such as shapes,
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connectors, and so on. Using Scheme, the application user could then
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write code that builds upon these basic operations to create more
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complex procedures. For example, given basic procedures to enumerate
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the objects on a page, to determine whether an object is a square, and
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to change the fill pattern of a single shape, the user can write a
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Scheme procedure to change the fill pattern of all squares on the
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current page:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define (change-squares'-fill-pattern new-pattern)
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(for-each-shape current-page
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(lambda (shape)
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(if (square? shape)
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(change-fill-pattern shape new-pattern)))))
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</pre></div>
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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="Dia-Steps.html">Four Steps Required to Add Guile</a>, Up: <a href="Extending-Dia.html">How One Might Extend Dia Using Guile</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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