119 lines
5.9 KiB
HTML
119 lines
5.9 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>Annotated Scheme Read (Guile Reference Manual)</title>
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<meta name="description" content="Annotated Scheme Read (Guile Reference Manual)">
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<meta name="keywords" content="Annotated Scheme Read (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="Read_002fLoad_002fEval_002fCompile.html" rel="up" title="Read/Load/Eval/Compile">
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<link href="Scheme-Write.html" rel="next" title="Scheme Write">
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<link href="Scheme-Read.html" rel="prev" title="Scheme Read">
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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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strong.def-name {font-family: monospace; font-weight: bold; font-size: larger}
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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="Annotated-Scheme-Read">
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<div class="nav-panel">
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<p>
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Next: <a href="Scheme-Write.html" accesskey="n" rel="next">Writing Scheme Values</a>, Previous: <a href="Scheme-Read.html" accesskey="p" rel="prev">Reading Scheme Code</a>, Up: <a href="Read_002fLoad_002fEval_002fCompile.html" accesskey="u" rel="up">Reading and Evaluating Scheme Code</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="Reading-Scheme-Code_002c-For-the-Compiler"><span>6.16.3 Reading Scheme Code, For the Compiler<a class="copiable-link" href="#Reading-Scheme-Code_002c-For-the-Compiler"> ¶</a></span></h4>
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<p>When something goes wrong with a Scheme program, the user will want to
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know how to fix it. This starts with identifying where the error
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occurred: we want to associate a source location with each component part
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of source code, and propagate that source location information through
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to the compiler or interpreter.
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</p>
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<p>For that, Guile provides <code class="code">read-syntax</code>.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-read_002dsyntax"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">read-syntax</strong> <var class="def-var-arguments">[port]</var><a class="copiable-link" href="#index-read_002dsyntax"> ¶</a></span></dt>
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<dd><p>Read an s-expression from the input port <var class="var">port</var>, or from the current
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input port if <var class="var">port</var> is not specified.
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</p>
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<p>If, after skipping white space and comments, no more bytes are available
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from <var class="var">port</var>, return the end-of-file object. See <a class="xref" href="Binary-I_002fO.html">Binary I/O</a>.
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Otherwise, return an annotated datum. An annotated datum is a syntax
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object which associates a source location with a datum. For example:
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</p>
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<div class="example">
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<pre class="example-preformatted">(call-with-input-string " foo" read-syntax)
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; ⇒ #<syntax:unknown file:1:2 foo>
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(call-with-input-string "(foo)" read-syntax)
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; ⇒
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; #<syntax:unknown file:1:0
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; (#<syntax unknown file:1:1 foo>)>
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</pre></div>
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<p>As the second example shows, all fields of pairs and vectors are also
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annotated, recursively.
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</p></dd></dl>
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<p>Most users are familiar with syntax objects in the context of macros,
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which use syntax objects to associate scope information with
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identifiers. See <a class="xref" href="Macros.html">Macros</a>. Here we use syntax objects to associate
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source location information with any datum, but without attaching scope
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information. The Scheme compiler (<code class="code">compile</code>) and the interpreter
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(<code class="code">eval</code>) can accept syntax objects directly as input, allowing them
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to associate source information with resulting code.
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See <a class="xref" href="Compilation.html">Compiling Scheme Code</a>, and See <a class="xref" href="Fly-Evaluation.html">Procedures for On the Fly Evaluation</a>.
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</p>
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<p>Note that there is a legacy interface for getting source locations into
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the Scheme compiler or interpreter, which is to use a side table that
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associates “source properties” with each subdatum returned by
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<code class="code">read</code>, instead of wrapping the datums directly as in
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<code class="code">read-syntax</code>. This has the disadvantage of not being able to
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annotate all kinds of datums. See <a class="xref" href="Source-Properties.html">Source Properties</a>, for more
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information.
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</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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Next: <a href="Scheme-Write.html">Writing Scheme Values</a>, Previous: <a href="Scheme-Read.html">Reading Scheme Code</a>, Up: <a href="Read_002fLoad_002fEval_002fCompile.html">Reading and Evaluating Scheme Code</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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