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3.7 KiB
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84 lines
3.7 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>Optional Arguments (Guile Reference Manual)</title>
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<div class="subsection-level-extent" id="Optional-Arguments">
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Next: <a href="Case_002dlambda.html" accesskey="n" rel="next">Case-lambda</a>, Previous: <a href="Compiled-Procedures.html" accesskey="p" rel="prev">Compiled Procedures</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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<h4 class="subsection" id="Optional-Arguments-1"><span>6.7.4 Optional Arguments<a class="copiable-link" href="#Optional-Arguments-1"> ¶</a></span></h4>
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<p>Scheme procedures, as defined in R5RS, can either handle a fixed number
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of actual arguments, or a fixed number of actual arguments followed by
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arbitrarily many additional arguments. Writing procedures of variable
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arity can be useful, but unfortunately, the syntactic means for handling
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argument lists of varying length is a bit inconvenient. It is possible
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to give names to the fixed number of arguments, but the remaining
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(optional) arguments can be only referenced as a list of values
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(see <a class="pxref" href="Lambda.html">Lambda: Basic Procedure Creation</a>).
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</p>
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<p>For this reason, Guile provides an extension to <code class="code">lambda</code>,
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<code class="code">lambda*</code>, which allows the user to define procedures with
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optional and keyword arguments. In addition, Guile’s virtual machine
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has low-level support for optional and keyword argument dispatch.
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Calls to procedures with optional and keyword arguments can be made
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cheaply, without allocating a rest list.
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</p>
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<ul class="mini-toc">
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<li><a href="lambda_002a-and-define_002a.html" accesskey="1">lambda* and define*.</a></li>
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<li><a href="ice_002d9-optargs.html" accesskey="2">(ice-9 optargs)</a></li>
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