195 lines
9.1 KiB
HTML
195 lines
9.1 KiB
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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>Compiler Tower (Guile Reference Manual)</title>
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<meta name="description" content="Compiler Tower (Guile Reference Manual)">
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<meta name="keywords" content="Compiler Tower (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="The-Scheme-Compiler.html" rel="next" title="The Scheme Compiler">
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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="Compiler-Tower">
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<div class="nav-panel">
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<p>
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Next: <a href="The-Scheme-Compiler.html" accesskey="n" rel="next">The Scheme Compiler</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="Compiler-Tower-1"><span>9.4.1 Compiler Tower<a class="copiable-link" href="#Compiler-Tower-1"> ¶</a></span></h4>
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<p>Guile’s compiler is quite simple – its <em class="emph">compilers</em>, to put it more
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accurately. Guile defines a tower of languages, starting at Scheme and
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progressively simplifying down to languages that resemble the VM
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instruction set (see <a class="pxref" href="Instruction-Set.html">Instruction Set</a>).
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</p>
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<p>Each language knows how to compile to the next, so each step is simple
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and understandable. Furthermore, this set of languages is not hardcoded
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into Guile, so it is possible for the user to add new high-level
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languages, new passes, or even different compilation targets.
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</p>
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<p>Languages are registered in the module, <code class="code">(system base language)</code>:
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</p>
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<div class="example">
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<pre class="example-preformatted">(use-modules (system base language))
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</pre></div>
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<p>They are registered with the <code class="code">define-language</code> form.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-define_002dlanguage"><span class="category-def">Scheme Syntax: </span><span><strong class="def-name">define-language</strong> <var class="def-var-arguments">[#:name] [#:title] [#:reader] [#:printer] [#:parser=#f] [#:compilers=’()] [#:decompilers=’()] [#:evaluator=#f] [#:joiner=#f] [#:for-humans?=#t] [#:make-default-environment=make-fresh-user-module] [#:lowerer=#f] [#:analyzer=#f] [#:compiler-chooser=#f]</var><a class="copiable-link" href="#index-define_002dlanguage"> ¶</a></span></dt>
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<dd><p>Define a language.
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</p>
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<p>This syntax defines a <code class="code"><language></code> object, bound to <var class="var">name</var> in
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the current environment. In addition, the language will be added to the
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global language set. For example, this is the language definition for
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Scheme:
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</p>
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<div class="example">
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<pre class="example-preformatted">(define-language scheme
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#:title "Scheme"
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#:reader (lambda (port env) ...)
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#:compilers `((tree-il . ,compile-tree-il))
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#:decompilers `((tree-il . ,decompile-tree-il))
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#:evaluator (lambda (x module) (primitive-eval x))
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#:printer write
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#:make-default-environment (lambda () ...))
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</pre></div>
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</dd></dl>
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<p>The interesting thing about having languages defined this way is that
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they present a uniform interface to the read-eval-print loop. This
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allows the user to change the current language of the REPL:
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</p>
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<div class="example">
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<pre class="example-preformatted">scheme@(guile-user)> ,language tree-il
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Happy hacking with Tree Intermediate Language! To switch back, type `,L scheme'.
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tree-il@(guile-user)> ,L scheme
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Happy hacking with Scheme! To switch back, type `,L tree-il'.
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scheme@(guile-user)>
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</pre></div>
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<p>Languages can be looked up by name, as they were above.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-lookup_002dlanguage"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">lookup-language</strong> <var class="def-var-arguments">name</var><a class="copiable-link" href="#index-lookup_002dlanguage"> ¶</a></span></dt>
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<dd><p>Looks up a language named <var class="var">name</var>, autoloading it if necessary.
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</p>
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<p>Languages are autoloaded by looking for a variable named <var class="var">name</var> in
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a module named <code class="code">(language <var class="var">name</var> spec)</code>.
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</p>
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<p>The language object will be returned, or <code class="code">#f</code> if there does not
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exist a language with that name.
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</p></dd></dl>
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<p>When Guile goes to compile Scheme to bytecode, it will ask the Scheme
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language to choose a compiler from Scheme to the next language on the
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path from Scheme to bytecode. Performing this computation recursively
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builds transformations from a flexible chain of compilers. The next
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link will be obtained by invoking the language’s compiler chooser, or if
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not present, from the language’s compilers field.
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</p>
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<p>A language can specify an analyzer, which is run before a term of that
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language is lowered and compiled. This is where compiler warnings are
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issued.
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</p>
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<p>If a language specifies a lowerer, that procedure is called on
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expressions before compilation. This is where optimizations and
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canonicalizations go.
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</p>
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<p>Finally a language’s compiler translates a lowered term from one
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language to the next one in the chain.
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</p>
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<p>There is a notion of a “current language”, which is maintained in the
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<code class="code">current-language</code> parameter, defined in the core <code class="code">(guile)</code>
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module. This language is normally Scheme, and may be rebound by the
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user. The run-time compilation interfaces
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(see <a class="pxref" href="Read_002fLoad_002fEval_002fCompile.html">Reading and Evaluating Scheme Code</a>) also allow you to choose other source
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and target languages.
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</p>
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<p>The normal tower of languages when compiling Scheme goes like this:
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</p>
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<ul class="itemize mark-bullet">
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<li>Scheme
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</li><li>Tree Intermediate Language (Tree-IL)
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</li><li>Continuation-Passing Style (CPS)
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</li><li>Bytecode
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</li></ul>
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<p>As discussed before (see <a class="pxref" href="Object-File-Format.html">Object File Format</a>), bytecode is in ELF
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format, ready to be serialized to disk. But when compiling Scheme at
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run time, you want a Scheme value: for example, a compiled procedure.
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For this reason, so as not to break the abstraction, Guile defines a
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fake language at the bottom of the tower:
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</p>
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<ul class="itemize mark-bullet">
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<li>Value
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</li></ul>
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<p>Compiling to <code class="code">value</code> loads the bytecode into a procedure, turning
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cold bytes into warm code.
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</p>
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<p>Perhaps this strangeness can be explained by example:
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<code class="code">compile-file</code> defaults to compiling to bytecode, because it
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produces object code that has to live in the barren world outside the
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Guile runtime; but <code class="code">compile</code> defaults to compiling to <code class="code">value</code>,
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as its product re-enters the Guile world.
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</p>
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<p>Indeed, the process of compilation can circulate through these
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different worlds indefinitely, as shown by the following quine:
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</p>
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<div class="example">
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<pre class="example-preformatted">((lambda (x) ((compile x) x)) '(lambda (x) ((compile x) x)))
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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="The-Scheme-Compiler.html">The Scheme Compiler</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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