docsrc/xlisp/xlisp-doc/reference/go.htm


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<html><head><title>XLISP go</title></head>

<link rel="stylesheet" type="text/css" href="reference.css">

</head>

<body>

<a href="../start.htm">Nyquist / XLISP 2.0</a>&nbsp; -&nbsp;
<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>go</h1>

<hr>

<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
  <td><nobr>Type:</nobr></td>
  <td><nobr>&nbsp;&nbsp;-&nbsp;&nbsp;</nobr></td>
  <td width="100%"><nobr>special form (fsubr)</nobr></td>
</tr>
<tr valign="top">
  <td><nobr>Source:</nobr></td>
  <td><nobr>&nbsp;&nbsp;-&nbsp;&nbsp;</nobr></td>
  <td width="100%"><nobr>xlcont.c</nobr></td>
</tr>
</tbody></table></p>

<h2>Syntax</h2>

<dl>
<dt>(go <i>tag-symbol</i>)</dt>
<dd><i>tag-symbol</i> - a symbol<br>
returns - never returns a value</dd>
</dl>

<h2>Description</h2>

<p>The 'go' special form allows 'goto' style branching within 'block' constructs
<nobr>[<a href="do.htm">do</a> ,</nobr>
<nobr><a href="do-star.htm">do*</a> ,</nobr>
<nobr><a href="dolist.htm">dolist</a> ,</nobr>
<nobr><a href="dotimes.htm">dotimes</a> ,</nobr>
<nobr><a href="tagbody.htm">tagbody</a> ,</nobr>
<nobr><a href="loop.htm">loop</a> ,</nobr>
<a href="prog.htm">prog</a> and
<a href="prog-star.htm">prog*</a>]. The
'tag-symbol' is the 'label' and must exist somewhere within the 'block'
that the 'go' occurs within. Otherwise an error will be generated:</p>

<pre class="example">
<font color="#AA0000">error: no target for GO</font>
</pre>

<p>'go' never returns a value. If the 'tag-symbol' exists, then
the execution will continue immediately after the'tag-symbol'.</p>

<h2>Examples</h2>

<pre class="example">
(defun foo (i j)                   <font color="#008844">; define FOO</font>
  (prog ()                         <font color="#008844">; with a PROG</font>
         (print "begin")
   start (print j)                 <font color="#008844">; tag - START</font>
         (setq j (1- j))
         (if (eql i j) (GO start)  <font color="#008844">; 2-way branch</font>
                       (GO end))
         (print "hello")           <font color="#008844">; won't ever be reached</font>
   end   (print "done")            <font color="#008844">; tag - END</font>
         (return 42)))

(foo 1 2)                          <font color="#008844">; prints  "begin" 2 1 "done"</font>
                                   <font color="#008844">;   returns 42</font>

(foo 2 1)                          <font color="#008844">; prints  "begin" 1 "done"</font>
                                   <font color="#008844">;   returns 42</font>
</pre>

<p><b>Note:</b> Although 'go' will accept a 'tag-symbol' that is not a
symbol, it will not find this improper 'tag-symbol'. An error will be
generated:</p>

<pre class="example">
<font color="#AA0000">error: no target for GO</font>
</pre>

<p>See the
<a href="../manual/xlisp-man-021.htm#go">go</a>
special form in the <nobr>XLISP 2.0</nobr> manual.</p>

<p><nobr>&nbsp;&nbsp;<a href="#top">Back to Top</nobr></a></p>

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<a href="../examples/examples.htm">Examples</a> |
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