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<html><head><title>XLISP decf</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
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<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>decf</h1>
<hr>
<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
<td><nobr>Type:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>Lisp macro (closure)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>misc.lsp</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<p><div class="box">
<dl>
<dt><nobr>(<b>decf</b> <i>symbol</i>)</nobr></dt>
<dd><i>symbol</i> - a symbol with numerical value bound to it<br>
returns - the new value of the symbol</dd>
</dl>
</div></p>
<p>In Nyquist, 'decf' is implemented as a Lisp macro:</p>
<pre class="example">
(defmacro <font color="#0000CC">decf</font> (symbol)
`(setf ,symbol (1- ,symbol)))
</pre>
<h2>Description</h2>
<p>The 'decf' macro is used for decrementing a numerical value of a variable.
<nobr>1 is</nobr> substracted to the number and the result is stored in the
variable. <nobr>An error</nobr> is signalled if the variable doesn't hold a
number.</p>
<h2>Examples</h2>
<pre class="example">
(setq n 3) => 3
(decf n) => 2
n => 2
(decf n) => 1
(setq n 1.8) => 1.8
(decf n) => 0.8
(decf n) => -0.2
(decf n) => -1.2
n => -1.2
(setq n #\a) => #\a
(decf a) => <font color="#AA0000">error: bad argument type - #\a</font>
</pre>
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