173 lines
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173 lines
12 KiB
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Copyright (C) 2021 Maxime Devos
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Copyright (C) 2024 Tomas Volf
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<title>Procedure Properties (Guile Reference Manual)</title>
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<meta name="description" content="Procedure Properties (Guile Reference Manual)">
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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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<div class="subsection-level-extent" id="Procedure-Properties">
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<p>
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Next: <a href="Procedures-with-Setters.html" accesskey="n" rel="next">Procedures with Setters</a>, Previous: <a href="Higher_002dOrder-Functions.html" accesskey="p" rel="prev">Higher-Order Functions</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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<hr>
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<h4 class="subsection" id="Procedure-Properties-and-Meta_002dinformation"><span>6.7.7 Procedure Properties and Meta-information<a class="copiable-link" href="#Procedure-Properties-and-Meta_002dinformation"> ¶</a></span></h4>
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<p>In addition to the information that is strictly necessary to run,
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procedures may have other associated information. For example, the
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name of a procedure is information not for the procedure, but about
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the procedure. This meta-information can be accessed via the procedure
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properties interface.
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</p>
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<a class="index-entry-id" id="index-procedure_003f-2"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-procedure_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-procedure_003f"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_p</strong> <var class="def-var-arguments">(obj)</var><a class="copiable-link" href="#index-scm_005fprocedure_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.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-thunk_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">thunk?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-thunk_003f"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fthunk_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_thunk_p</strong> <var class="def-var-arguments">(obj)</var><a class="copiable-link" href="#index-scm_005fthunk_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 that can be called with
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zero arguments. See <a class="xref" href="Compiled-Procedures.html">Compiled Procedures</a>, to get more information
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on what arguments a procedure will accept.
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</p></dd></dl>
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<a class="index-entry-id" id="index-procedure-properties"></a>
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<p>Procedure properties are general properties associated with
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procedures. These can be the name of a procedure or other relevant
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information, such as debug hints.
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</p>
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<p>The most general way to associate a property of a procedure is
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programmatically:
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-procedure_002dproperty"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure-property</strong> <var class="def-var-arguments">proc key</var><a class="copiable-link" href="#index-procedure_002dproperty"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fproperty"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_property</strong> <var class="def-var-arguments">(proc, key)</var><a class="copiable-link" href="#index-scm_005fprocedure_005fproperty"> ¶</a></span></dt>
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<dd><p>Return the property of <var class="var">proc</var> with name <var class="var">key</var>, or <code class="code">#f</code> if
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not found.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-set_002dprocedure_002dproperty_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">set-procedure-property!</strong> <var class="def-var-arguments">proc key value</var><a class="copiable-link" href="#index-set_002dprocedure_002dproperty_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fset_005fprocedure_005fproperty_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_set_procedure_property_x</strong> <var class="def-var-arguments">(proc, key, value)</var><a class="copiable-link" href="#index-scm_005fset_005fprocedure_005fproperty_005fx"> ¶</a></span></dt>
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<dd><p>Set <var class="var">proc</var>’s property named <var class="var">key</var> to <var class="var">value</var>.
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</p></dd></dl>
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<p>However, there is a more efficient interface that allows constant
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properties to be embedded into compiled binaries in a way that does
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not incur any overhead until someone asks for the property: initial
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non-tail elements of the body of a lambda expression that are literal
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vectors of pairs are interpreted as declaring procedure properties.
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This is easiest to see with an example:
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</p>
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<div class="example">
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<pre class="example-preformatted">(define proc
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(lambda args
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#((a . "hey") (b . "ho")) ;; procedure properties!
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42))
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(procedure-property proc 'a) ; ⇒ "hey"
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(procedure-property proc 'b) ; ⇒ "ho"
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</pre></div>
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<p>There is a shorthand for declaring the <code class="code">documentation</code> property,
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which is a literal string instead of a literal vector:
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</p>
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<div class="example">
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<pre class="example-preformatted">(define proc
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(lambda args
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"This is a docstring."
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42))
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(procedure-property proc 'documentation)
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;; ⇒ "This is a docstring."
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</pre></div>
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<p>Calling <code class="code">procedure-property</code> with a key of <code class="code">documentation</code>
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is exactly the same as calling <code class="code">procedure-documentation</code>.
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Similarly, <code class="code">procedure-name</code> is the same as the <code class="code">name</code>
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procedure property, and <code class="code">procedure-source</code> is for the
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<code class="code">source</code> property.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-procedure_002dname"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure-name</strong> <var class="def-var-arguments">proc</var><a class="copiable-link" href="#index-procedure_002dname"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fname"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_name</strong> <var class="def-var-arguments">(proc)</var><a class="copiable-link" href="#index-scm_005fprocedure_005fname"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-procedure_002dsource"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure-source</strong> <var class="def-var-arguments">proc</var><a class="copiable-link" href="#index-procedure_002dsource"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fsource"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_source</strong> <var class="def-var-arguments">(proc)</var><a class="copiable-link" href="#index-scm_005fprocedure_005fsource"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-procedure_002ddocumentation"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure-documentation</strong> <var class="def-var-arguments">proc</var><a class="copiable-link" href="#index-procedure_002ddocumentation"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fdocumentation"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_documentation</strong> <var class="def-var-arguments">(proc)</var><a class="copiable-link" href="#index-scm_005fprocedure_005fdocumentation"> ¶</a></span></dt>
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<dd><p>Return the value of the <code class="code">name</code>, <code class="code">source</code>, or
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<code class="code">documentation</code> property for <var class="var">proc</var>, or <code class="code">#f</code> if no
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property is set.
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</p></dd></dl>
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<p>One can also work on the entire set of procedure properties.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-procedure_002dproperties"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">procedure-properties</strong> <var class="def-var-arguments">proc</var><a class="copiable-link" href="#index-procedure_002dproperties"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fprocedure_005fproperties"><span class="category-def">C Function: </span><span><strong class="def-name">scm_procedure_properties</strong> <var class="def-var-arguments">(proc)</var><a class="copiable-link" href="#index-scm_005fprocedure_005fproperties"> ¶</a></span></dt>
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<dd><p>Return the properties associated with <var class="var">proc</var>, as an association
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list.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-set_002dprocedure_002dproperties_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">set-procedure-properties!</strong> <var class="def-var-arguments">proc alist</var><a class="copiable-link" href="#index-set_002dprocedure_002dproperties_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fset_005fprocedure_005fproperties_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_set_procedure_properties_x</strong> <var class="def-var-arguments">(proc, alist)</var><a class="copiable-link" href="#index-scm_005fset_005fprocedure_005fproperties_005fx"> ¶</a></span></dt>
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<dd><p>Set <var class="var">proc</var>’s property list to <var class="var">alist</var>.
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</p></dd></dl>
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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="Procedures-with-Setters.html">Procedures with Setters</a>, Previous: <a href="Higher_002dOrder-Functions.html">Higher-Order Functions</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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