155 lines
8.1 KiB
HTML
155 lines
8.1 KiB
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<!DOCTYPE html>
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<html>
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<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
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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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under the terms of the GNU Free Documentation License, Version 1.3 or
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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>SRFI-1 Predicates (Guile Reference Manual)</title>
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<meta name="description" content="SRFI-1 Predicates (Guile Reference Manual)">
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<meta name="keywords" content="SRFI-1 Predicates (Guile Reference Manual)">
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<link href="index.html" rel="start" title="Top">
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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="SRFI_002d1.html" rel="up" title="SRFI-1">
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<link href="SRFI_002d1-Selectors.html" rel="next" title="SRFI-1 Selectors">
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<link href="SRFI_002d1-Constructors.html" rel="prev" title="SRFI-1 Constructors">
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<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
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</head>
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<body lang="en">
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<div class="subsubsection-level-extent" id="SRFI_002d1-Predicates">
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<div class="nav-panel">
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<p>
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Next: <a href="SRFI_002d1-Selectors.html" accesskey="n" rel="next">Selectors</a>, Previous: <a href="SRFI_002d1-Constructors.html" accesskey="p" rel="prev">Constructors</a>, Up: <a href="SRFI_002d1.html" accesskey="u" rel="up">SRFI-1 - List library</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="subsubsection" id="Predicates"><span>7.5.3.2 Predicates<a class="copiable-link" href="#Predicates"> ¶</a></span></h4>
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<a class="index-entry-id" id="index-list-predicate"></a>
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<p>The procedures in this section test specific properties of lists.
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</p>
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<dl class="first-deffn">
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<dt class="deffn" id="index-proper_002dlist_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">proper-list?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-proper_002dlist_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a proper list, or <code class="code">#f</code>
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otherwise. This is the same as the core <code class="code">list?</code> (see <a class="pxref" href="List-Predicates.html">List Predicates</a>).
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</p>
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<p>A proper list is a list which ends with the empty list <code class="code">()</code> in
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the usual way. The empty list <code class="code">()</code> itself is a proper list too.
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</p>
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<div class="example">
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<pre class="example-preformatted">(proper-list? '(1 2 3)) ⇒ #t
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(proper-list? '()) ⇒ #t
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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-circular_002dlist_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">circular-list?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-circular_002dlist_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a circular list, or <code class="code">#f</code>
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otherwise.
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</p>
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<p>A circular list is a list where at some point the <code class="code">cdr</code> refers
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back to a previous pair in the list (either the start or some later
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point), so that following the <code class="code">cdr</code>s takes you around in a
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circle, with no end.
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</p>
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<div class="example">
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<pre class="example-preformatted">(define x (list 1 2 3 4))
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(set-cdr! (last-pair x) (cddr x))
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x ⇒ (1 2 3 4 3 4 3 4 ...)
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(circular-list? x) ⇒ #t
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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-dotted_002dlist_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">dotted-list?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-dotted_002dlist_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a dotted list, or <code class="code">#f</code>
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otherwise.
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</p>
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<p>A dotted list is a list where the <code class="code">cdr</code> of the last pair is not
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the empty list <code class="code">()</code>. Any non-pair <var class="var">obj</var> is also considered a
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dotted list, with length zero.
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</p>
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<div class="example">
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<pre class="example-preformatted">(dotted-list? '(1 2 . 3)) ⇒ #t
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(dotted-list? 99) ⇒ #t
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</pre></div>
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</dd></dl>
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<p>It will be noted that any Scheme object passes exactly one of the
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above three tests <code class="code">proper-list?</code>, <code class="code">circular-list?</code> and
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<code class="code">dotted-list?</code>. Non-lists are <code class="code">dotted-list?</code>, finite lists
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are either <code class="code">proper-list?</code> or <code class="code">dotted-list?</code>, and infinite
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lists are <code class="code">circular-list?</code>.
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</p>
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<br>
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<dl class="first-deffn">
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<dt class="deffn" id="index-null_002dlist_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">null-list?</strong> <var class="def-var-arguments">lst</var><a class="copiable-link" href="#index-null_002dlist_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if <var class="var">lst</var> is the empty list <code class="code">()</code>, <code class="code">#f</code>
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otherwise. If something else than a proper or circular list is passed
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as <var class="var">lst</var>, an error is signaled. This procedure is recommended
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for checking for the end of a list in contexts where dotted lists are
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not allowed.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-not_002dpair_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">not-pair?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-not_002dpair_003f"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> is <var class="var">obj</var> is not a pair, <code class="code">#f</code> otherwise.
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This is shorthand notation <code class="code">(not (pair? <var class="var">obj</var>))</code> and is
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supposed to be used for end-of-list checking in contexts where dotted
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lists are allowed.
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</p></dd></dl>
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<dl class="first-deffn">
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<dt class="deffn" id="index-list_003d"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">list=</strong> <var class="def-var-arguments">elt= list1 …</var><a class="copiable-link" href="#index-list_003d"> ¶</a></span></dt>
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<dd><p>Return <code class="code">#t</code> if all argument lists are equal, <code class="code">#f</code> otherwise.
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List equality is determined by testing whether all lists have the same
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length and the corresponding elements are equal in the sense of the
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equality predicate <var class="var">elt=</var>. If no or only one list is given,
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<code class="code">#t</code> is returned.
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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="SRFI_002d1-Selectors.html">Selectors</a>, Previous: <a href="SRFI_002d1-Constructors.html">Constructors</a>, Up: <a href="SRFI_002d1.html">SRFI-1 - List library</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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</html>
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