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<html><head><title>XLISP :tmacro</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>:tmacro</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>keyword</nobr></td>
</tr>
<tr valign="top">
<td><nobr>Source:</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>xlread.c</nobr></td>
</tr>
</tbody></table></p>
<h2>Syntax</h2>
<dl>
<dt>(:tmacro . <i>function</i>)</dt>
<dd><i>function</i> - a function</dd>
</dl>
<h2>Description</h2>
<p>':tmacro' is an entry that is used in the
<a href="global-readtable.htm">*readtable*</a> system variable that contains
XLISP's data structures relating to the processing of characters from the
user [or files] and read-macro expansions. The existance of the ':tmacro'
keyword means that the specified character is the start of a terminal read
macro. For ':tmacro', the form of the
<a href="global-readtable.htm">*readtable*</a> entry is a dotted pair
like:</p>
<pre class="example">
(:tmacro . <font color="#008844"><i>function</i></font>)
</pre>
<p>The 'function' can be a built-in read-macro function or a user defined
lambda expression. The 'function' takes two parameters, an input stream
specification, and an integer that is the character value. The 'function'
should return <a href="nil.htm">NIL</a> if the character is
'white-space' or a value <a href="cons.htm">cons</a>ed with
<a href="nil.htm">NIL</a> to return the value. The 'function'
will probably read additional characters from the input stream.</p>
<h2>Examples</h2>
<pre class="example">
(defun look-at (table) <font color="#008844">; define a function to look in a table</font>
(dotimes (ch 127) <font color="#008844">; and print out any :TMACRO entries</font>
(prog ((entry (aref table ch)))
(if (and (consp entry)
(equal (car entry) ':TMACRO))
(princ (int-char ch)))))
(terpri))
(look-at *readtable*) <font color="#008844">; prints "'(),;`</font>
</pre>
<p><b>Note:</b> The system defines that the following are ':tmacro'
characters:</p>
<pre>
\ " ` , ( ) ;
</pre>
<p>[backslash, double quote, backquote, comma, opening parenthesis, closing
parenthesis, semicolon.]</p>
<p><b>Caution:</b> If you experiment with
<nobr><a href="global-readtable.htm">*readtable*</a> ,</nobr> it is useful
to save the old value in a variable, so that you can restore the system
state.</p>
<p>See the
<a href="../manual/xlisp-man-008.htm#tmacro">:tmacro</a>
keyword in the <nobr>XLISP 2.0</nobr> manual.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
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