154 lines
6.9 KiB
HTML
154 lines
6.9 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>The Scheme Compiler (Guile Reference Manual)</title>
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<meta name="description" content="The Scheme Compiler (Guile Reference Manual)">
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<meta name="keywords" content="The Scheme Compiler (Guile Reference Manual)">
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<meta name="resource-type" content="document">
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<meta name="distribution" content="global">
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<meta name="Generator" content=".texi2any-real">
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<meta name="viewport" content="width=device-width,initial-scale=1">
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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="Compiling-to-the-Virtual-Machine.html" rel="up" title="Compiling to the Virtual Machine">
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<link href="Tree_002dIL.html" rel="next" title="Tree-IL">
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<link href="Compiler-Tower.html" rel="prev" title="Compiler Tower">
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<style type="text/css">
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a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
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span:hover a.copiable-link {visibility: visible}
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-->
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</style>
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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="subsection-level-extent" id="The-Scheme-Compiler">
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<div class="nav-panel">
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<p>
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Next: <a href="Tree_002dIL.html" accesskey="n" rel="next">Tree-IL</a>, Previous: <a href="Compiler-Tower.html" accesskey="p" rel="prev">Compiler Tower</a>, Up: <a href="Compiling-to-the-Virtual-Machine.html" accesskey="u" rel="up">Compiling to the Virtual Machine</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="The-Scheme-Compiler-1"><span>9.4.2 The Scheme Compiler<a class="copiable-link" href="#The-Scheme-Compiler-1"> ¶</a></span></h4>
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<p>The job of the Scheme compiler is to expand all macros and all of Scheme
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to its most primitive expressions. The definition of “primitive
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expression” is given by the inventory of constructs provided by
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Tree-IL, the target language of the Scheme compiler: procedure calls,
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conditionals, lexical references, and so on. This is described more
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fully in the next section.
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</p>
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<p>The tricky and amusing thing about the Scheme-to-Tree-IL compiler is
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that it is completely implemented by the macro expander. Since the
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macro expander has to run over all of the source code already in order
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to expand macros, it might as well do the analysis at the same time,
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producing Tree-IL expressions directly.
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</p>
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<p>Because this compiler is actually the macro expander, it is extensible.
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Any macro which the user writes becomes part of the compiler.
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</p>
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<p>The Scheme-to-Tree-IL expander may be invoked using the generic
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<code class="code">compile</code> procedure:
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(compile '(+ 1 2) #:from 'scheme #:to 'tree-il)
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⇒
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#<tree-il (call (toplevel +) (const 1) (const 2))>
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</pre></div>
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<p><code class="code">(compile <var class="var">foo</var> #:from 'scheme #:to 'tree-il)</code> is entirely
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equivalent to calling the macro expander as <code class="code">(macroexpand <var class="var">foo</var>
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'c '(compile load eval))</code>. See <a class="xref" href="Macro-Expansion.html">Macro Expansion</a>.
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<code class="code">compile-tree-il</code>, the procedure dispatched by <code class="code">compile</code> to
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<code class="code">'tree-il</code>, is a small wrapper around <code class="code">macroexpand</code>, to make
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it conform to the general form of compiler procedures in Guile’s
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language tower.
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</p>
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<p>Compiler procedures take three arguments: an expression, an
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environment, and a keyword list of options. They return three values:
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the compiled expression, the corresponding environment for the target
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language, and a “continuation environment”. The compiled expression
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and environment will serve as input to the next language’s compiler.
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The “continuation environment” can be used to compile another
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expression from the same source language within the same module.
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</p>
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<p>For example, you might compile the expression, <code class="code">(define-module
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(foo))</code>. This will result in a Tree-IL expression and environment. But
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if you compiled a second expression, you would want to take into account
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the compile-time effect of compiling the previous expression, which puts
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the user in the <code class="code">(foo)</code> module. That is the purpose of the
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“continuation environment”; you would pass it as the environment when
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compiling the subsequent expression.
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</p>
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<p>For Scheme, an environment is a module. By default, the <code class="code">compile</code>
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and <code class="code">compile-file</code> procedures compile in a fresh module, such
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that bindings and macros introduced by the expression being compiled
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are isolated:
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</p>
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<div class="example">
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<pre class="example-preformatted">(eq? (current-module) (compile '(current-module)))
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⇒ #f
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(compile '(define hello 'world))
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(defined? 'hello)
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⇒ #f
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(define / *)
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(eq? (compile '/) /)
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⇒ #f
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</pre></div>
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<p>Similarly, changes to the <code class="code">current-reader</code> fluid (see <a class="pxref" href="Loading.html"><code class="code">current-reader</code></a>) are isolated:
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</p>
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<div class="example">
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<pre class="example-preformatted">(compile '(fluid-set! current-reader (lambda args 'fail)))
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(fluid-ref current-reader)
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⇒ #f
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</pre></div>
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<p>Nevertheless, having the compiler and <em class="dfn">compilee</em> share the same name
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space can be achieved by explicitly passing <code class="code">(current-module)</code> as
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the compilation environment:
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</p>
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<div class="example">
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<pre class="example-preformatted">(define hello 'world)
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(compile 'hello #:env (current-module))
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⇒ world
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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="Tree_002dIL.html">Tree-IL</a>, Previous: <a href="Compiler-Tower.html">Compiler Tower</a>, Up: <a href="Compiling-to-the-Virtual-Machine.html">Compiling to the Virtual Machine</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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