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<html><head><title>XLISP prog*</title>
<link rel="stylesheet" type="text/css" href="reference.css">
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>prog*</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>special form (fsubr)</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xlcont.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<dl>
<dt>(prog* ([<i>binding</i> ... ]) [<i>expr</i> ... ])</dt>
<dd><i>binding</i> - a variable binding which is can take one of
<dl><dd><i>symbol</i><br>
(<i>symbol init-expr</i>)</dd>
<dl><dd><i>symbol</i> - a symbol<br>
<i>init-expr</i> - an initialization expression for <i>symbol</i></dd></dl></dl>
<i>expr</i> - expressions comprising the body of the loop which may contain
<a href="return.htm">return</a>s,
<a href="go.htm">go</a>s or tags for
<a href="go.htm">go</a><br>
returns - <a href="nil.htm">NIL</a> or the argument passed to
the <a href="return.htm">return</a> function</dd>
</dl>
<h2>Description</h2>
<p>The 'prog*' special form is basically a 'block' construct that contains
symbols with optional initializations and a block of code [expressions] to
evaluate. The 'prog*' special form evaluates its initializations in
sequential order as opposed to <a href="">prog</a> which does it in no
specified order. The first form after the 'prog*' is the 'binding' form. It
contains a series of 'symbols' or 'bindings'. The 'binding' is a 'symbol'
followed by an initialization expression 'init-expr'. If there is no
'init-expr', the 'symbol' will be initialized to
<a href="nil.htm">NIL</a>. The order of execution of the bindings
is sequential. If a <a href="return.htm">return</a> form is
evaluated, its value will be returned. Otherwise,
<a href="nil.htm">NIL</a> is returned. When the 'prog*' is
finished execution, the 'symbols' that were defined will no longer exist or
retain their values.</p>
<h2>Examples</h2>
<pre class="example">
(prog* (i j) <font color="#008844">; PROG* with vars I and J</font>
(print i) (print j)) <font color="#008844">; prints NIL NIL returns NIL</font>
(prog* ((i 1) (j 2)) <font color="#008844">; PROG* with vars I and J</font>
(print i) (print j)
(return (+ i j))) <font color="#008844">; prints 1 2 returns 3</font>
(prog* () (print "hello")) <font color="#008844">; prints "hello" returns NIL</font>
(prog ((i 1) (j (+ i 1))) <font color="#008844">; PROG won't work due to order</font>
(print (+ i j)) ) <font color="#008844">; error: unbound variable - I</font>
(prog* ((i 1) (j (+ i 1))) <font color="#008844">; PROG* will work due to order</font>
(print (+ i j)) ) <font color="#008844">; prints 3 returns NIL</font>
</pre>
<p>See the
<a href="../manual/xlisp-man-021.htm#prog*">prog*</a>
special form in the <nobr>XLISP 2.0</nobr> manual.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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<a href="../manual/contents.htm">Contents</a> |
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