178 lines
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178 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>Mapping Folding and Unfolding (Guile Reference Manual)</title>
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<div class="subsubsection-level-extent" id="Mapping-Folding-and-Unfolding">
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<p>
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Next: <a href="Miscellaneous-String-Operations.html" accesskey="n" rel="next">Miscellaneous String Operations</a>, Previous: <a href="Reversing-and-Appending-Strings.html" accesskey="p" rel="prev">Reversing and Appending Strings</a>, Up: <a href="Strings.html" accesskey="u" rel="up">Strings</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="subsubsection" id="Mapping_002c-Folding_002c-and-Unfolding"><span>6.6.5.11 Mapping, Folding, and Unfolding<a class="copiable-link" href="#Mapping_002c-Folding_002c-and-Unfolding"> ¶</a></span></h4>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dmap"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-map</strong> <var class="def-var-arguments">proc s [start [end]]</var><a class="copiable-link" href="#index-string_002dmap"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005fmap"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_map</strong> <var class="def-var-arguments">(proc, s, start, end)</var><a class="copiable-link" href="#index-scm_005fstring_005fmap"> ¶</a></span></dt>
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<dd><p><var class="var">proc</var> is a char->char procedure, it is mapped over
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<var class="var">s</var>. The order in which the procedure is applied to the
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string elements is not specified.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dmap_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-map!</strong> <var class="def-var-arguments">proc s [start [end]]</var><a class="copiable-link" href="#index-string_002dmap_0021"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005fmap_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_map_x</strong> <var class="def-var-arguments">(proc, s, start, end)</var><a class="copiable-link" href="#index-scm_005fstring_005fmap_005fx"> ¶</a></span></dt>
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<dd><p><var class="var">proc</var> is a char->char procedure, it is mapped over
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<var class="var">s</var>. The order in which the procedure is applied to the
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string elements is not specified. The string <var class="var">s</var> is
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modified in-place, the return value is not specified.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dfor_002deach"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-for-each</strong> <var class="def-var-arguments">proc s [start [end]]</var><a class="copiable-link" href="#index-string_002dfor_002deach"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005ffor_005feach"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_for_each</strong> <var class="def-var-arguments">(proc, s, start, end)</var><a class="copiable-link" href="#index-scm_005fstring_005ffor_005feach"> ¶</a></span></dt>
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<dd><p><var class="var">proc</var> is mapped over <var class="var">s</var> in left-to-right order. The
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return value is not specified.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dfor_002deach_002dindex"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-for-each-index</strong> <var class="def-var-arguments">proc s [start [end]]</var><a class="copiable-link" href="#index-string_002dfor_002deach_002dindex"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005ffor_005feach_005findex"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_for_each_index</strong> <var class="def-var-arguments">(proc, s, start, end)</var><a class="copiable-link" href="#index-scm_005fstring_005ffor_005feach_005findex"> ¶</a></span></dt>
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<dd><p>Call <code class="code">(<var class="var">proc</var> i)</code> for each index i in <var class="var">s</var>, from left to
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right.
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</p>
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<p>For example, to change characters to alternately upper and lower case,
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</p>
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<div class="example">
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<pre class="example-preformatted">(define str (string-copy "studly"))
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(string-for-each-index
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(lambda (i)
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(string-set! str i
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((if (even? i) char-upcase char-downcase)
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(string-ref str i))))
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str)
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str ⇒ "StUdLy"
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</pre></div>
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</dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dfold"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-fold</strong> <var class="def-var-arguments">kons knil s [start [end]]</var><a class="copiable-link" href="#index-string_002dfold"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005ffold"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_fold</strong> <var class="def-var-arguments">(kons, knil, s, start, end)</var><a class="copiable-link" href="#index-scm_005fstring_005ffold"> ¶</a></span></dt>
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<dd><p>Fold <var class="var">kons</var> over the characters of <var class="var">s</var>, with <var class="var">knil</var>
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as the terminating element, from left to right. <var class="var">kons</var>
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must expect two arguments: The actual character and the last
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result of <var class="var">kons</var>’ application.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dfold_002dright"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-fold-right</strong> <var class="def-var-arguments">kons knil s [start [end]]</var><a class="copiable-link" href="#index-string_002dfold_002dright"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005ffold_005fright"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_fold_right</strong> <var class="def-var-arguments">(kons, knil, s, start, end)</var><a class="copiable-link" href="#index-scm_005fstring_005ffold_005fright"> ¶</a></span></dt>
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<dd><p>Fold <var class="var">kons</var> over the characters of <var class="var">s</var>, with <var class="var">knil</var>
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as the terminating element, from right to left. <var class="var">kons</var>
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must expect two arguments: The actual character and the last
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result of <var class="var">kons</var>’ application.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dunfold"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-unfold</strong> <var class="def-var-arguments">p f g seed [base [make_final]]</var><a class="copiable-link" href="#index-string_002dunfold"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005funfold"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_unfold</strong> <var class="def-var-arguments">(p, f, g, seed, base, make_final)</var><a class="copiable-link" href="#index-scm_005fstring_005funfold"> ¶</a></span></dt>
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<dd><ul class="itemize mark-bullet">
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<li><var class="var">g</var> is used to generate a series of <em class="emph">seed</em>
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values from the initial <var class="var">seed</var>: <var class="var">seed</var>, (<var class="var">g</var>
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<var class="var">seed</var>), (<var class="var">g</var>^2 <var class="var">seed</var>), (<var class="var">g</var>^3 <var class="var">seed</var>),
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…
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</li><li><var class="var">p</var> tells us when to stop – when it returns true
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when applied to one of these seed values.
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</li><li><var class="var">f</var> maps each seed value to the corresponding
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character in the result string. These chars are assembled
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into the string in a left-to-right order.
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</li><li><var class="var">base</var> is the optional initial/leftmost portion
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of the constructed string; it default to the empty
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string.
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</li><li><var class="var">make_final</var> is applied to the terminal seed
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value (on which <var class="var">p</var> returns true) to produce
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the final/rightmost portion of the constructed string.
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The default is nothing extra.
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</li></ul>
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</dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-string_002dunfold_002dright"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">string-unfold-right</strong> <var class="def-var-arguments">p f g seed [base [make_final]]</var><a class="copiable-link" href="#index-string_002dunfold_002dright"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fstring_005funfold_005fright"><span class="category-def">C Function: </span><span><strong class="def-name">scm_string_unfold_right</strong> <var class="def-var-arguments">(p, f, g, seed, base, make_final)</var><a class="copiable-link" href="#index-scm_005fstring_005funfold_005fright"> ¶</a></span></dt>
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<dd><ul class="itemize mark-bullet">
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<li><var class="var">g</var> is used to generate a series of <em class="emph">seed</em>
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values from the initial <var class="var">seed</var>: <var class="var">seed</var>, (<var class="var">g</var>
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<var class="var">seed</var>), (<var class="var">g</var>^2 <var class="var">seed</var>), (<var class="var">g</var>^3 <var class="var">seed</var>),
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…
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</li><li><var class="var">p</var> tells us when to stop – when it returns true
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when applied to one of these seed values.
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</li><li><var class="var">f</var> maps each seed value to the corresponding
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character in the result string. These chars are assembled
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into the string in a right-to-left order.
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</li><li><var class="var">base</var> is the optional initial/rightmost portion
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of the constructed string; it default to the empty
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string.
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</li><li><var class="var">make_final</var> is applied to the terminal seed
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value (on which <var class="var">p</var> returns true) to produce
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the final/leftmost portion of the constructed string.
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It defaults to <code class="code">(lambda (x) )</code>.
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</li></ul>
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</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="Miscellaneous-String-Operations.html">Miscellaneous String Operations</a>, Previous: <a href="Reversing-and-Appending-Strings.html">Reversing and Appending Strings</a>, Up: <a href="Strings.html">Strings</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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