119 lines
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119 lines
4.4 KiB
HTML
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Keyword Read Syntax (Guile Reference Manual)</title>
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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="Keywords.html" rel="up" title="Keywords">
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<link href="Keyword-Procedures.html" rel="next" title="Keyword Procedures">
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<div class="subsubsection-level-extent" id="Keyword-Read-Syntax">
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Next: <a href="Keyword-Procedures.html" accesskey="n" rel="next">Keyword Procedures</a>, Previous: <a href="Coding-With-Keywords.html" accesskey="p" rel="prev">Coding With Keywords</a>, Up: <a href="Keywords.html" accesskey="u" rel="up">Keywords</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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<hr>
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<h4 class="subsubsection" id="Keyword-Read-Syntax-1"><span>6.6.7.3 Keyword Read Syntax<a class="copiable-link" href="#Keyword-Read-Syntax-1"> ¶</a></span></h4>
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<p>Guile, by default, only recognizes a keyword syntax that is compatible
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with R5RS. A token of the form <code class="code">#:NAME</code>, where <code class="code">NAME</code> has the
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same syntax as a Scheme symbol (see <a class="pxref" href="Symbol-Read-Syntax.html">Extended Read Syntax for Symbols</a>), is the
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external representation of the keyword named <code class="code">NAME</code>. Keyword
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objects print using this syntax as well, so values containing keyword
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objects can be read back into Guile. When used in an expression,
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keywords are self-quoting objects.
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</p>
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<p>If the <code class="code">keywords</code> read option is set to <code class="code">'prefix</code>, Guile also
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recognizes the alternative read syntax <code class="code">:NAME</code>. Otherwise, tokens
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of the form <code class="code">:NAME</code> are read as symbols, as required by R5RS.
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</p>
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<a class="index-entry-id" id="index-SRFI_002d88-keyword-syntax"></a>
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<p>If the <code class="code">keywords</code> read option is set to <code class="code">'postfix</code>, Guile
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recognizes the SRFI-88 read syntax <code class="code">NAME:</code> (see <a class="pxref" href="SRFI_002d88.html">SRFI-88 Keyword Objects</a>).
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Otherwise, tokens of this form are read as symbols.
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</p>
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<p>To enable and disable the alternative non-R5RS keyword syntax, you use
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the <code class="code">read-set!</code> procedure documented <a class="ref" href="Scheme-Read.html">Reading Scheme Code</a>. Note that
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the <code class="code">prefix</code> and <code class="code">postfix</code> syntax are mutually exclusive.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(read-set! keywords 'prefix)
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#:type
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⇒
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#:type
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:type
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⇒
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#:type
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(read-set! keywords 'postfix)
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type:
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⇒
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#:type
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:type
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⇒
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:type
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(read-set! keywords #f)
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#:type
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⇒
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#:type
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:type
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-|
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ERROR: In expression :type:
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ERROR: Unbound variable: :type
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ABORT: (unbound-variable)
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</pre></div>
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</div>
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