96 lines
4 KiB
HTML
96 lines
4 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>Lexical Scope (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="About-Closure.html" rel="up" title="About Closure">
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<link href="Closure.html" rel="next" title="Closure">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Lexical-Scope">
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<div class="nav-panel">
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<p>
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Next: <a href="Closure.html" accesskey="n" rel="next">Closure</a>, Previous: <a href="Chaining.html" accesskey="p" rel="prev">Environment Chaining</a>, Up: <a href="About-Closure.html" accesskey="u" rel="up">The Concept of Closure</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="Lexical-Scope-1"><span>3.4.4 Lexical Scope<a class="copiable-link" href="#Lexical-Scope-1"> ¶</a></span></h4>
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<p>The rules that we have just been describing are the details of how
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Scheme implements “lexical scoping”. This subsection takes a brief
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diversion to explain what lexical scope means in general and to present
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an example of non-lexical scoping.
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</p>
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<p>“Lexical scope” in general is the idea that
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</p>
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<ul class="itemize mark-bullet">
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<li>an identifier at a particular place in a program always refers to the
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same variable location — where “always” means “every time that the
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containing expression is executed”, and that
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</li><li>the variable location to which it refers can be determined by static
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examination of the source code context in which that identifier appears,
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without having to consider the flow of execution through the program as
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a whole.
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</li></ul>
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<p>In practice, lexical scoping is the norm for most programming languages,
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and probably corresponds to what you would intuitively consider to be
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“normal”. You may even be wondering how the situation could possibly
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— and usefully — be otherwise. To demonstrate that another kind of
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scoping is possible, therefore, and to compare it against lexical
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scoping, the following subsection presents an example of non-lexical
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scoping and examines in detail how its behavior differs from the
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corresponding lexically scoped code.
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</p>
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<ul class="mini-toc">
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<li><a href="Scoping-Example.html" accesskey="1">An Example of Non-Lexical Scoping</a></li>
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</ul>
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</div>
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</body>
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</html>
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