158 lines
8.4 KiB
HTML
158 lines
8.4 KiB
HTML
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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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any later version published by the Free Software Foundation; with no
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copy of the license is included in the section entitled "GNU Free
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<title>Procedures with Setters (Guile Reference Manual)</title>
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<link href="Procedures.html" rel="up" title="Procedures">
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<body lang="en">
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<div class="subsection-level-extent" id="Procedures-with-Setters">
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<div class="nav-panel">
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<p>
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Next: <a href="Inlinable-Procedures.html" accesskey="n" rel="next">Inlinable Procedures</a>, Previous: <a href="Procedure-Properties.html" accesskey="p" rel="prev">Procedure Properties and Meta-information</a>, Up: <a href="Procedures.html" accesskey="u" rel="up">Procedures</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="Procedures-with-Setters-1"><span>6.7.8 Procedures with Setters<a class="copiable-link" href="#Procedures-with-Setters-1"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-procedure-with-setter"></a>
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<a class="index-entry-id" id="index-setter"></a>
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<p>A <em class="dfn">procedure with setter</em> is a special kind of procedure which
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normally behaves like any accessor procedure, that is a procedure which
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accesses a data structure. The difference is that this kind of
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procedure has a so-called <em class="dfn">setter</em> attached, which is a procedure
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for storing something into a data structure.
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</p>
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<p>Procedures with setters are treated specially when the procedure appears
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in the special form <code class="code">set!</code>. How it works is best shown by example.
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</p>
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<p>Suppose we have a procedure called <code class="code">foo-ref</code>, which accepts two
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arguments, a value of type <code class="code">foo</code> and an integer. The procedure
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returns the value stored at the given index in the <code class="code">foo</code> object.
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Let <code class="code">f</code> be a variable containing such a <code class="code">foo</code> data
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structure.<a class="footnote" id="DOCF12" href="#FOOT12"><sup>12</sup></a>
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(foo-ref f 0) ⇒ bar
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(foo-ref f 1) ⇒ braz
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</pre></div>
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<p>Also suppose that a corresponding setter procedure called
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<code class="code">foo-set!</code> does exist.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(foo-set! f 0 'bla)
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(foo-ref f 0) ⇒ bla
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</pre></div>
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<p>Now we could create a new procedure called <code class="code">foo</code>, which is a
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procedure with setter, by calling <code class="code">make-procedure-with-setter</code> with
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the accessor and setter procedures <code class="code">foo-ref</code> and <code class="code">foo-set!</code>.
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Let us call this new procedure <code class="code">foo</code>.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(define foo (make-procedure-with-setter foo-ref foo-set!))
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</pre></div>
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<p><code class="code">foo</code> can from now on be used to either read from the data
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structure stored in <code class="code">f</code>, or to write into the structure.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(set! (foo f 0) 'dum)
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(foo f 0) ⇒ dum
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</pre></div>
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<dl class="first-deffn">
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<dt class="deffn" id="index-make_002dprocedure_002dwith_002dsetter"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-procedure-with-setter</strong> <var class="def-var-arguments">procedure setter</var><a class="copiable-link" href="#index-make_002dprocedure_002dwith_002dsetter"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fmake_005fprocedure_005fwith_005fsetter"><span class="category-def">C Function: </span><span><strong class="def-name">scm_make_procedure_with_setter</strong> <var class="def-var-arguments">(procedure, setter)</var><a class="copiable-link" href="#index-scm_005fmake_005fprocedure_005fwith_005fsetter"> ¶</a></span></dt>
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<dd><p>Create a new procedure which behaves like <var class="var">procedure</var>, but
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with the associated setter <var class="var">setter</var>.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-procedure_002dwith_002dsetter_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure-with-setter?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-procedure_002dwith_002dsetter_003f"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fwith_005fsetter_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_with_setter_p</strong> <var class="def-var-arguments">(obj)</var><a class="copiable-link" href="#index-scm_005fprocedure_005fwith_005fsetter_005fp"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a procedure with an
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associated setter procedure.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-procedure"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure</strong> <var class="def-var-arguments">proc</var><a class="copiable-link" href="#index-procedure"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure</strong> <var class="def-var-arguments">(proc)</var><a class="copiable-link" href="#index-scm_005fprocedure"> ¶</a></span></dt>
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<dd><p>Return the procedure of <var class="var">proc</var>, which must be an
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applicable struct.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-setter-1"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">setter</strong> <var class="def-var-arguments">proc</var><a class="copiable-link" href="#index-setter-1"> ¶</a></span></dt>
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<dd><p>Return the setter of <var class="var">proc</var>, which must be either a procedure with
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setter or an operator struct.
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</p></dd></dl>
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</div>
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<div class="footnotes-segment">
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<hr>
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<h4 class="footnotes-heading">Footnotes</h4>
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<h5 class="footnote-body-heading"><a id="FOOT12" href="#DOCF12">(12)</a></h5>
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<p>Working definitions would be:
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</p><div class="example lisp">
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<pre class="lisp-preformatted">(define foo-ref vector-ref)
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(define foo-set! vector-set!)
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(define f (make-vector 2 #f))
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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="Inlinable-Procedures.html">Inlinable Procedures</a>, Previous: <a href="Procedure-Properties.html">Procedure Properties and Meta-information</a>, Up: <a href="Procedures.html">Procedures</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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