167 lines
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167 lines
9.2 KiB
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html>
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<!-- Created by GNU Texinfo 6.8, 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 describes ASDF, a system definition facility
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for Common Lisp programs and libraries.
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You can find the latest version of this manual at
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https://common-lisp.net/project/asdf/asdf.html.
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ASDF Copyright (C) 2001-2019 Daniel Barlow and contributors.
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This manual Copyright (C) 2001-2019 Daniel Barlow and contributors.
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This manual revised (C) 2009-2019 Robert P. Goldman and Francois-Rene Rideau.
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Permission is hereby granted, free of charge, to any person obtaining
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a copy of this software and associated documentation files (the
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"Software"), to deal in the Software without restriction, including
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without limitation the rights to use, copy, modify, merge, publish,
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distribute, sublicense, and/or sell copies of the Software, and to
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permit persons to whom the Software is furnished to do so, subject to
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the following conditions:
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The above copyright notice and this permission notice shall be
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included in all copies or substantial portions of the Software.
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THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
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EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
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NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
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LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
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OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
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WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
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-->
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<title>How do I work with readtables? (ASDF Manual)</title>
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<meta name="description" content="How do I work with readtables? (ASDF Manual)">
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<meta name="keywords" content="How do I work with readtables? (ASDF Manual)">
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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="Issues-with-using-and-extending-ASDF-to-define-systems.html" rel="up" title="Issues with using and extending ASDF to define systems">
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<link href="How-can-I-capture-ASDF_0027s-output_003f.html" rel="next" title="How can I capture ASDF's output?">
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<link href="How-do-I-mark-a-source-file-to-be-loaded-only-and-not-compiled_003f.html" rel="prev" title="How do I mark a source file to be loaded only and not compiled?">
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</head>
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<body lang="en">
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<div class="subsection" id="How-do-I-work-with-readtables_003f">
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<div class="header">
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<p>
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Next: <a href="How-can-I-capture-ASDF_0027s-output_003f.html" accesskey="n" rel="next">How can I capture ASDF’s output?</a>, Previous: <a href="How-do-I-mark-a-source-file-to-be-loaded-only-and-not-compiled_003f.html" accesskey="p" rel="prev">How do I mark a source file to be loaded only and not compiled?</a>, Up: <a href="Issues-with-using-and-extending-ASDF-to-define-systems.html" accesskey="u" rel="up">Issues with using and extending ASDF to define systems</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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<span id="How-do-I-work-with-readtables_003f-1"></span><h4 class="subsection">13.6.7 How do I work with readtables?</h4>
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<span id="index-readtables"></span>
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<p>It is possible to configure the lisp syntax by modifying the currently-active readtable.
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However, this same readtable is shared globally by all software being compiled by ASDF,
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especially since <code>load</code> and <code>compile-file</code> both bind <var>*readtable*</var>,
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so that its value is the same across the build at the start of every file
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(unless overridden by some <code>perform :around</code> method),
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even if a file locally binds it to a different readtable during the build.
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</p>
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<p>Therefore, the following hygiene restrictions apply. If you don’t abide by these restrictions,
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there will be situations where your output files will be corrupted during an incremental build.
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We are not trying to prescribe new restrictions for the sake of good style:
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these restrictions have always applied implicitly, and
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we are simply describing what they have always been.
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</p>
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<ul>
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<li> It is forbidden to modifying any standard character or standard macro dispatch defined in the CLHS.
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</li><li> No two dependencies may assign different meanings to the same non-standard character.
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</li><li> Using any non-standard character while expecting the implementation to treat some way
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counts as such an assignment of meaning.
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</li><li> libraries need to document these assignments of meaning to non-standard characters.
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</li><li> free software libraries will register these changes on:
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<a href="http://www.cliki.net/Macro%20Characters">http://www.cliki.net/Macro%20Characters</a>
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</li></ul>
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<p>If you want to use readtable modifications that cannot abide by those restrictions,
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you <em>must</em> create a different readtable object and set <var>*readtable*</var>
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to temporarily bind it to your new readtable (which will be undone after processing the file).
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</p>
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<p>For that, we recommend you use system <code>named-readtables</code>
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to define or combine such readtables using <code>named-readtables:defreadtable</code>
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and use them using <code>named-readtables:in-readtable</code>.
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Equivalently, you can use system <code>cl-syntax</code>,
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that itself uses <code>named-readtables</code>,
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but may someday do more with, e.g. <var>*print-pprint-dispatch*</var>.
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</p>
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<p>For even more advanced syntax modification beyond what a readtable can express,
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you may consider either:
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</p><ul>
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<li> a <code>perform</code> method that compiles a constant file that contains a single form
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<code>#.*code-read-with-alternate-reader*</code> in an environment where this special variable
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was bound to the code read by your alternate reader, or
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</li><li> using the system <code>reader-interception</code>.
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</li></ul>
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<p>Beware that it is unsafe to use ASDF from the REPL to compile or load systems
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while the readtable isn’t the shared readtable previously used to build software.
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You <em>must</em> manually undo any binding of <var>*readtable*</var> at the REPL
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and restore its initial value whenever you call <code>operate</code>
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(via e.g. <code>load-system</code>, <code>test-system</code> or <code>require</code>)
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from a REPL that is using a different readtable.
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</p>
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<ul class="section-toc">
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<li><a href="How-do-I-work-with-readtables_003f.html#How-should-my-system-use-a-readtable-exported-by-another-system_003f" accesskey="1">How should my system use a readtable exported by another system?</a></li>
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<li><a href="How-do-I-work-with-readtables_003f.html#How-should-my-library-make-a-readtable-available-to-other-systems_003f" accesskey="2">How should my library make a readtable available to other systems?</a></li>
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</ul>
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<div class="subsubsection" id="How-should-my-system-use-a-readtable-exported-by-another-system_003f">
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<h4 class="subsubsection">13.6.7.1 How should my system use a readtable exported by another system?</h4>
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<p>Use from the <code>named-readtables</code> system the macro <code>named-readtables:in-readtable</code>.
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</p>
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<p>If the other system fails to use <code>named-readtables</code>, fix it and send a patch upstream.
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In the day and age of Quicklisp and clbuild, there is little reason
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to eschew using such an important library anymore.
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</p>
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</div>
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<div class="subsubsection" id="How-should-my-library-make-a-readtable-available-to-other-systems_003f">
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<h4 class="subsubsection">13.6.7.2 How should my library make a readtable available to other systems?</h4>
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<p>Use from the <code>named-readtables</code> system the macro <code>named-readtables:defreadtable</code>.
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</p>
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</div>
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</div>
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<hr>
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<div class="header">
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<p>
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Next: <a href="How-can-I-capture-ASDF_0027s-output_003f.html">How can I capture ASDF’s output?</a>, Previous: <a href="How-do-I-mark-a-source-file-to-be-loaded-only-and-not-compiled_003f.html">How do I mark a source file to be loaded only and not compiled?</a>, Up: <a href="Issues-with-using-and-extending-ASDF-to-define-systems.html">Issues with using and extending ASDF to define systems</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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