155 lines
10 KiB
HTML
155 lines
10 KiB
HTML
|
<!DOCTYPE html>
|
||
|
|
<html>
|
||
|
|
<!-- Created by GNU Texinfo 7.1, https://www.gnu.org/software/texinfo/ -->
|
||
|
|
<head>
|
||
|
|
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
|
||
|
|
<!-- This manual documents Guile version 3.0.10.
|
||
|
|
|
||
|
|
Copyright (C) 1996-1997, 2000-2005, 2009-2023 Free Software Foundation,
|
||
|
|
Inc.
|
||
|
|
|
||
|
|
Copyright (C) 2021 Maxime Devos
|
||
|
|
|
||
|
|
Copyright (C) 2024 Tomas Volf
|
||
|
|
|
||
|
|
|
||
|
|
Permission is granted to copy, distribute and/or modify this document
|
||
|
|
under the terms of the GNU Free Documentation License, Version 1.3 or
|
||
|
|
any later version published by the Free Software Foundation; with no
|
||
|
|
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A
|
||
|
|
copy of the license is included in the section entitled "GNU Free
|
||
|
|
Documentation License." -->
|
||
|
|
<title>Variables (Guile Reference Manual)</title>
|
||
|
|
|
||
|
|
<meta name="description" content="Variables (Guile Reference Manual)">
|
||
|
|
<meta name="keywords" content="Variables (Guile Reference Manual)">
|
||
|
|
<meta name="resource-type" content="document">
|
||
|
|
<meta name="distribution" content="global">
|
||
|
|
<meta name="Generator" content=".texi2any-real">
|
||
|
|
<meta name="viewport" content="width=device-width,initial-scale=1">
|
||
|
|
|
||
|
|
<link href="index.html" rel="start" title="Top">
|
||
|
|
<link href="Concept-Index.html" rel="index" title="Concept Index">
|
||
|
|
<link href="index.html#SEC_Contents" rel="contents" title="Table of Contents">
|
||
|
|
<link href="Modules.html" rel="up" title="Modules">
|
||
|
|
<link href="Module-System-Reflection.html" rel="next" title="Module System Reflection">
|
||
|
|
<link href="R6RS-Libraries.html" rel="prev" title="R6RS Libraries">
|
||
|
|
<style type="text/css">
|
||
|
|
<!--
|
||
|
|
a.copiable-link {visibility: hidden; text-decoration: none; line-height: 0em}
|
||
|
|
div.example {margin-left: 3.2em}
|
||
|
|
span:hover a.copiable-link {visibility: visible}
|
||
|
|
strong.def-name {font-family: monospace; font-weight: bold; font-size: larger}
|
||
|
|
-->
|
||
|
|
</style>
|
||
|
|
<link rel="stylesheet" type="text/css" href="https://www.gnu.org/software/gnulib/manual.css">
|
||
|
|
|
||
|
|
|
||
|
|
</head>
|
||
|
|
|
||
|
|
<body lang="en">
|
||
|
|
<div class="subsection-level-extent" id="Variables">
|
||
|
|
<div class="nav-panel">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Module-System-Reflection.html" accesskey="n" rel="next">Module System Reflection</a>, Previous: <a href="R6RS-Libraries.html" accesskey="p" rel="prev">R6RS Libraries</a>, Up: <a href="Modules.html" accesskey="u" rel="up">Modules</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>
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<h4 class="subsection" id="Variables-1"><span>6.18.7 Variables<a class="copiable-link" href="#Variables-1"> ¶</a></span></h4>
|
||
|
|
<a class="index-entry-id" id="index-Variables"></a>
|
||
|
|
|
||
|
|
<p>Each module has its own hash table, sometimes known as an <em class="dfn">obarray</em>,
|
||
|
|
that maps the names defined in that module to their corresponding
|
||
|
|
variable objects.
|
||
|
|
</p>
|
||
|
|
<p>A variable is a box-like object that can hold any Scheme value. It is
|
||
|
|
said to be <em class="dfn">undefined</em> if its box holds a special Scheme value that
|
||
|
|
denotes undefined-ness (which is different from all other Scheme values,
|
||
|
|
including for example <code class="code">#f</code>); otherwise the variable is
|
||
|
|
<em class="dfn">defined</em>.
|
||
|
|
</p>
|
||
|
|
<p>On its own, a variable object is anonymous. A variable is said to be
|
||
|
|
<em class="dfn">bound</em> when it is associated with a name in some way, usually a
|
||
|
|
symbol in a module obarray. When this happens, the name is said to be
|
||
|
|
bound to the variable, in that module.
|
||
|
|
</p>
|
||
|
|
<p>(That’s the theory, anyway. In practice, defined-ness and bound-ness
|
||
|
|
sometimes get confused, because Lisp and Scheme implementations have
|
||
|
|
often conflated — or deliberately drawn no distinction between — a
|
||
|
|
name that is unbound and a name that is bound to a variable whose value
|
||
|
|
is undefined. We will try to be clear about the difference and explain
|
||
|
|
any confusion where it is unavoidable.)
|
||
|
|
</p>
|
||
|
|
<p>Variables do not have a read syntax. Most commonly they are created and
|
||
|
|
bound implicitly by <code class="code">define</code> expressions: a top-level <code class="code">define</code>
|
||
|
|
expression of the form
|
||
|
|
</p>
|
||
|
|
<div class="example lisp">
|
||
|
|
<pre class="lisp-preformatted">(define <var class="var">name</var> <var class="var">value</var>)
|
||
|
|
</pre></div>
|
||
|
|
|
||
|
|
<p>creates a variable with initial value <var class="var">value</var> and binds it to the
|
||
|
|
name <var class="var">name</var> in the current module. But they can also be created
|
||
|
|
dynamically by calling one of the constructor procedures
|
||
|
|
<code class="code">make-variable</code> and <code class="code">make-undefined-variable</code>.
|
||
|
|
</p>
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-make_002dundefined_002dvariable"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-undefined-variable</strong><a class="copiable-link" href="#index-make_002dundefined_002dvariable"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fmake_005fundefined_005fvariable"><span class="category-def">C Function: </span><span><strong class="def-name">scm_make_undefined_variable</strong> <var class="def-var-arguments">()</var><a class="copiable-link" href="#index-scm_005fmake_005fundefined_005fvariable"> ¶</a></span></dt>
|
||
|
|
<dd><p>Return a variable that is initially unbound.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-make_002dvariable"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">make-variable</strong> <var class="def-var-arguments">init</var><a class="copiable-link" href="#index-make_002dvariable"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fmake_005fvariable"><span class="category-def">C Function: </span><span><strong class="def-name">scm_make_variable</strong> <var class="def-var-arguments">(init)</var><a class="copiable-link" href="#index-scm_005fmake_005fvariable"> ¶</a></span></dt>
|
||
|
|
<dd><p>Return a variable initialized to value <var class="var">init</var>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-variable_002dbound_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">variable-bound?</strong> <var class="def-var-arguments">var</var><a class="copiable-link" href="#index-variable_002dbound_003f"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fvariable_005fbound_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_variable_bound_p</strong> <var class="def-var-arguments">(var)</var><a class="copiable-link" href="#index-scm_005fvariable_005fbound_005fp"> ¶</a></span></dt>
|
||
|
|
<dd><p>Return <code class="code">#t</code> if <var class="var">var</var> is bound to a value, or <code class="code">#f</code>
|
||
|
|
otherwise. Throws an error if <var class="var">var</var> is not a variable object.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-variable_002dref"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">variable-ref</strong> <var class="def-var-arguments">var</var><a class="copiable-link" href="#index-variable_002dref"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fvariable_005fref"><span class="category-def">C Function: </span><span><strong class="def-name">scm_variable_ref</strong> <var class="def-var-arguments">(var)</var><a class="copiable-link" href="#index-scm_005fvariable_005fref"> ¶</a></span></dt>
|
||
|
|
<dd><p>Dereference <var class="var">var</var> and return its value.
|
||
|
|
<var class="var">var</var> must be a variable object; see <code class="code">make-variable</code>
|
||
|
|
and <code class="code">make-undefined-variable</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-variable_002dset_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">variable-set!</strong> <var class="def-var-arguments">var val</var><a class="copiable-link" href="#index-variable_002dset_0021"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fvariable_005fset_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_variable_set_x</strong> <var class="def-var-arguments">(var, val)</var><a class="copiable-link" href="#index-scm_005fvariable_005fset_005fx"> ¶</a></span></dt>
|
||
|
|
<dd><p>Set the value of the variable <var class="var">var</var> to <var class="var">val</var>.
|
||
|
|
<var class="var">var</var> must be a variable object, <var class="var">val</var> can be any
|
||
|
|
value. Return an unspecified value.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-variable_002dunset_0021"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">variable-unset!</strong> <var class="def-var-arguments">var</var><a class="copiable-link" href="#index-variable_002dunset_0021"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fvariable_005funset_005fx"><span class="category-def">C Function: </span><span><strong class="def-name">scm_variable_unset_x</strong> <var class="def-var-arguments">(var)</var><a class="copiable-link" href="#index-scm_005fvariable_005funset_005fx"> ¶</a></span></dt>
|
||
|
|
<dd><p>Unset the value of the variable <var class="var">var</var>, leaving <var class="var">var</var> unbound.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
<dl class="first-deffn">
|
||
|
|
<dt class="deffn" id="index-variable_003f"><span class="category-def">Scheme Procedure: </span><span><strong class="def-name">variable?</strong> <var class="def-var-arguments">obj</var><a class="copiable-link" href="#index-variable_003f"> ¶</a></span></dt>
|
||
|
|
<dt class="deffnx def-cmd-deffn" id="index-scm_005fvariable_005fp"><span class="category-def">C Function: </span><span><strong class="def-name">scm_variable_p</strong> <var class="def-var-arguments">(obj)</var><a class="copiable-link" href="#index-scm_005fvariable_005fp"> ¶</a></span></dt>
|
||
|
|
<dd><p>Return <code class="code">#t</code> if <var class="var">obj</var> is a variable object, else return
|
||
|
|
<code class="code">#f</code>.
|
||
|
|
</p></dd></dl>
|
||
|
|
|
||
|
|
|
||
|
|
</div>
|
||
|
|
<hr>
|
||
|
|
<div class="nav-panel">
|
||
|
|
<p>
|
||
|
|
Next: <a href="Module-System-Reflection.html">Module System Reflection</a>, Previous: <a href="R6RS-Libraries.html">R6RS Libraries</a>, Up: <a href="Modules.html">Modules</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>
|
||
|
|
</div>
|
||
|
|
|
||
|
|
|
||
|
|
|
||
|
|
</body>
|
||
|
|
</html>
|