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256 lines
27 KiB
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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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Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
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copy of the license is included in the section entitled "GNU Free
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Documentation License." -->
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<title>Pairs (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="Data-Types.html" rel="up" title="Data Types">
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</head>
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<body lang="en">
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<div class="subsection-level-extent" id="Pairs">
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<div class="nav-panel">
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<p>
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Next: <a href="Lists.html" accesskey="n" rel="next">Lists</a>, Previous: <a href="Keywords.html" accesskey="p" rel="prev">Keywords</a>, Up: <a href="Data-Types.html" accesskey="u" rel="up">Data Types</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="Pairs-1"><span>6.6.8 Pairs<a class="copiable-link" href="#Pairs-1"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-Pairs"></a>
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<p>Pairs are used to combine two Scheme objects into one compound object.
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Hence the name: A pair stores a pair of objects.
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</p>
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<p>The data type <em class="dfn">pair</em> is extremely important in Scheme, just like in
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any other Lisp dialect. The reason is that pairs are not only used to
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make two values available as one object, but that pairs are used for
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constructing lists of values. Because lists are so important in Scheme,
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they are described in a section of their own (see <a class="pxref" href="Lists.html">Lists</a>).
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</p>
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<p>Pairs can literally get entered in source code or at the REPL, in the
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so-called <em class="dfn">dotted list</em> syntax. This syntax consists of an opening
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parentheses, the first element of the pair, a dot, the second element
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and a closing parentheses. The following example shows how a pair
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consisting of the two numbers 1 and 2, and a pair containing the symbols
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<code class="code">foo</code> and <code class="code">bar</code> can be entered. It is very important to write
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the whitespace before and after the dot, because otherwise the Scheme
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parser would not be able to figure out where to split the tokens.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">(1 . 2)
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(foo . bar)
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</pre></div>
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<p>But beware, if you want to try out these examples, you have to
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<em class="dfn">quote</em> the expressions. More information about quotation is
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available in the section <a class="ref" href="Expression-Syntax.html">Expression Syntax</a>. The correct way
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to try these examples is as follows.
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</p>
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<div class="example lisp">
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<pre class="lisp-preformatted">'(1 . 2)
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⇒
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(1 . 2)
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'(foo . bar)
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⇒
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(foo . bar)
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</pre></div>
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<p>A new pair is made by calling the procedure <code class="code">cons</code> with two
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arguments. Then the argument values are stored into a newly allocated
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pair, and the pair is returned. The name <code class="code">cons</code> stands for
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"construct". Use the procedure <code class="code">pair?</code> to test whether a
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given Scheme object is a pair or not.
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</p>
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<a class="index-entry-id" id="index-cons-2"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-cons"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cons</strong> <var class="def-var-arguments">x y</var><a class="copiable-link" href="#index-cons"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcons"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cons</strong> <var class="def-var-arguments">(x, y)</var><a class="copiable-link" href="#index-scm_005fcons"> ¶</a></span></dt>
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<dd><p>Return a newly allocated pair whose car is <var class="var">x</var> and whose
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cdr is <var class="var">y</var>. The pair is guaranteed to be different (in the
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sense of <code class="code">eq?</code>) from every previously existing object.
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</p></dd></dl>
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<a class="index-entry-id" id="index-pair_003f-3"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-pair_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">pair?</strong> <var class="def-var-arguments">x</var><a class="copiable-link" href="#index-pair_003f"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fpair_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_pair_p</strong> <var class="def-var-arguments">(x)</var><a class="copiable-link" href="#index-scm_005fpair_005fp"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">x</var> is a pair; otherwise return
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<code class="code">#f</code>.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-scm_005fis_005fpair"><span class="category-def">C Function: </span><span><code class="def-type">int</code> <strong class="def-name">scm_is_pair</strong> <code class="def-code-arguments">(SCM x)</code><a class="copiable-link" href="#index-scm_005fis_005fpair"> ¶</a></span></dt>
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<dd><p>Return 1 when <var class="var">x</var> is a pair; otherwise return 0.
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</p></dd></dl>
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<p>The two parts of a pair are traditionally called <em class="dfn">car</em> and
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<em class="dfn">cdr</em>. They can be retrieved with procedures of the same name
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(<code class="code">car</code> and <code class="code">cdr</code>), and can be modified with the procedures
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<code class="code">set-car!</code> and <code class="code">set-cdr!</code>.
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</p>
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<p>Since a very common operation in Scheme programs is to access the car of
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a car of a pair, or the car of the cdr of a pair, etc., the procedures
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called <code class="code">caar</code>, <code class="code">cadr</code> and so on are also predefined. However,
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using these procedures is often detrimental to readability, and
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error-prone. Thus, accessing the contents of a list is usually better
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achieved using pattern matching techniques (see <a class="pxref" href="Pattern-Matching.html">Pattern Matching</a>).
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</p>
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<a class="index-entry-id" id="index-car-2"></a>
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<a class="index-entry-id" id="index-cdr-2"></a>
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<dl class="first-deffn">
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<dt class="deffn" id="index-car"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">car</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-car"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_car</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdr"> ¶</a></span></dt>
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<dd><p>Return the car or the cdr of <var class="var">pair</var>, respectively.
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</p></dd></dl>
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<dl class="first-deftypefn">
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<dt class="deftypefn" id="index-SCM_005fCAR"><span class="category-def">C Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CAR</strong> <code class="def-code-arguments">(SCM pair)</code><a class="copiable-link" href="#index-SCM_005fCAR"> ¶</a></span></dt>
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<dt class="deftypefnx def-cmd-deftypefn" id="index-SCM_005fCDR"><span class="category-def">C Macro: </span><span><code class="def-type">SCM</code> <strong class="def-name">SCM_CDR</strong> <code class="def-code-arguments">(SCM pair)</code><a class="copiable-link" href="#index-SCM_005fCDR"> ¶</a></span></dt>
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<dd><p>These two macros are the fastest way to access the car or cdr of a
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pair; they can be thought of as compiling into a single memory
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reference.
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</p>
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<p>These macros do no checking at all. The argument <var class="var">pair</var> must be a
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valid pair.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-cddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cddar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cddar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cddar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdaar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdaar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdaar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cadar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cadar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cadar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caaar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caaar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caaar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cddddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cddddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cddddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdddar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdddar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdddar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cddadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cddadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cddadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cddaar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cddaar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cddaar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdaddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdaddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdaddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdadar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdadar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdadar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdaadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdaadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdaadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cdaaar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cdaaar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cdaaar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cadddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cadddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cadddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caddar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caddar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caddar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cadadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cadadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cadadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-cadaar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">cadaar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-cadaar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caaddr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caaddr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caaddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caadar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caadar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caadar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caaadr"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caaadr</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caaadr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-caaaar"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">caaaar</strong> <var class="def-var-arguments">pair</var><a class="copiable-link" href="#index-caaaar"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcddr"> ¶</a></span></dt>
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdar"> ¶</a></span></dt>
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||
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcadr"> ¶</a></span></dt>
|
||
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdddr"> ¶</a></span></dt>
|
||
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcddar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cddar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcddar"> ¶</a></span></dt>
|
||
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdadr"> ¶</a></span></dt>
|
||
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdaar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdaar"> ¶</a></span></dt>
|
||
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaddr"> ¶</a></span></dt>
|
||
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|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcadar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cadar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcadar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaadr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caaar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaaar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcddddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cddddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcddddr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdddar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdddar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdddar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcddadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cddadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcddadr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcddaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cddaar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcddaar"> ¶</a></span></dt>
|
||
|
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<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdaddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdaddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdaddr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdadar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdadar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdadar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdaadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdaadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdaadr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcdaaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cdaaar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcdaaar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcadddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cadddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcadddr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaddar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caddar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaddar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcadadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cadadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcadadr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcadaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_cadaar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcadaar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaaddr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caaddr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaaddr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaadar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caadar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaadar"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaaadr"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caaadr</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaaadr"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fcaaaar"><span class="category-def">C Function: </span><span><strong class="def-name">scm_caaaar</strong> <var class="def-var-arguments">(pair)</var><a class="copiable-link" href="#index-scm_005fcaaaar"> ¶</a></span></dt>
|
||
|
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<dd><p>These procedures are compositions of <code class="code">car</code> and <code class="code">cdr</code>, where
|
||
|
|
for example <code class="code">caddr</code> could be defined by
|
||
|
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</p>
|
||
|
|
<div class="example lisp">
|
||
|
|
<pre class="lisp-preformatted">(define caddr (lambda (x) (car (cdr (cdr x)))))
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p><code class="code">cadr</code>, <code class="code">caddr</code> and <code class="code">cadddr</code> pick out the second, third
|
||
|
|
or fourth elements of a list, respectively. SRFI-1 provides the same
|
||
|
|
under the names <code class="code">second</code>, <code class="code">third</code> and <code class="code">fourth</code>
|
||
|
|
(see <a class="pxref" href="SRFI_002d1-Selectors.html">Selectors</a>).
|
||
|
|
</p></dd></dl>
|
||
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|
||
|
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<a class="index-entry-id" id="index-set_002dcar_0021-1"></a>
|
||
|
|
<dl class="first-deffn">
|
||
|
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<dt class="deffn" id="index-set_002dcar_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">set-car!</strong> <var class="def-var-arguments">pair value</var><a class="copiable-link" href="#index-set_002dcar_0021"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fset_005fcar_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_set_car_x</strong> <var class="def-var-arguments">(pair, value)</var><a class="copiable-link" href="#index-scm_005fset_005fcar_005fx"> ¶</a></span></dt>
|
||
|
|
<dd><p>Stores <var class="var">value</var> in the car field of <var class="var">pair</var>. The value returned
|
||
|
|
by <code class="code">set-car!</code> is unspecified.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<a class="index-entry-id" id="index-set_002dcdr_0021-1"></a>
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-set_002dcdr_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">set-cdr!</strong> <var class="def-var-arguments">pair value</var><a class="copiable-link" href="#index-set_002dcdr_0021"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fset_005fcdr_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_set_cdr_x</strong> <var class="def-var-arguments">(pair, value)</var><a class="copiable-link" href="#index-scm_005fset_005fcdr_005fx"> ¶</a></span></dt>
|
||
|
|
<dd><p>Stores <var class="var">value</var> in the cdr field of <var class="var">pair</var>. The value returned
|
||
|
|
by <code class="code">set-cdr!</code> is unspecified.
|
||
|
|
</p></dd></dl>
|
||
|
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|
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|
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</div>
|
||
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<hr>
|
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<div class="nav-panel">
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||
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<p>
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Next: <a href="Lists.html">Lists</a>, Previous: <a href="Keywords.html">Keywords</a>, Up: <a href="Data-Types.html">Data Types</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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