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<html><head><title>XLISP *readtable*</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="../tutorials/tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="reference-index.htm">Reference</a>
<hr>
<h1>*readtable*</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>system variable</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> *readtable*</dt>
</dl>
<h2>Description</h2>
<p> The *readtable* is 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 table is 128 entries [0..127] for each of the
7-bit <a href="../misc/ascii-table.htm">ASCII</a> characters that
XLISP can read. Each entry in the *readtable* array must be one of
<nobr><a href="nil.htm">NIL</a> ,</nobr>
<nobr><a href="keyword-constituent.htm">:constituent</a> ,</nobr>
<nobr><a href="keyword-white-space.htm">:white-space</a> ,</nobr>
<nobr><a href="keyword-sescape.htm">:sescape</a> ,</nobr>
<nobr><a href="keyword-mescape.htm">:mescape</a> ,</nobr> a
<a href="keyword-tmacro.htm">:tmacro</a> dotted pair or a
<a href="keyword-nmacro.htm">:nmacro</a> dotted pair with the meaning
of:</p>
<p><table cellpadding="0" cellspacing="0" style="margin-left:10px"><tbody>
<tr valign="top">
<td><nobr><code> NIL</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>the character is invalid</nobr></td>
<td width="100%"><nobr> [see
<a href="nil.htm">nil</a>]</nobr></td>
</tr>
<tr valign="top">
<td><nobr><code>:CONSTITUENT</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>the character is valid, as is</nobr></td>
<td width="100%"><nobr> [see
<a href="keyword-constituent.htm">:constituent</a>]</nobr></td>
</tr>
<tr valign="top">
<td><nobr><code>:WHITE-SPACE</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>the character may be skipped over</nobr></td>
<td width="100%"><nobr> [see
<a href="keyword-white-space.htm">:white-space</a>]</nobr></td>
</tr>
<tr valign="top">
<td><nobr><code>:SESCAPE</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>the single escape character '\'</nobr></td>
<td width="100%"><nobr> [see
<a href="keyword-sescape.htm">:sescape</a>]</nobr></td>
</tr>
<tr valign="top">
<td><nobr><code>:MESCAPE</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>the multiple escape character '|'</nobr></td>
<td width="100%"><nobr> [see
<a href="keyword-mescape.htm">:mescape</a>]</nobr></td>
</tr>
<tr valign="top">
<td><nobr><code>(:TMACRO . <i>fun</i>)</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>a terminating readmacro</nobr></td>
<td width="100%"><nobr> [see
<a href="keyword-tmacro.htm">:tmacro</a>]</nobr></td>
</tr>
<tr valign="top">
<td><nobr><code>(:NMACRO . <i>fun</i>)</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>a non-terminating readmacro</nobr></td>
<td width="100%"><nobr> [see
<a href="keyword-nmacro.htm">:nmacro</a>]</nobr></td>
</tr>
</tbody></table></p>
<p>In the case of <a href="keyword-nmacro.htm">:nmacro</a> and
<nobr><a href="keyword-tmacro.htm">:tmacro</a> ,</nobr> the form of the
*readtable* entry is a list like:</p>
<pre class="example">
(:tmacro . <font color="#008844"><i>function</i></font>)
(:nmacro . <font color="#008844"><i>function</i></font>)
</pre>
<p>The 'function' can be a built-in read-macro function or a user defined
<a href="lambda.htm">lambda</a> 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.</p>
<h2>Examples</h2>
<pre class="example">
*readtable* <font color="#008844">; returns the current table</font>
<font color="#008844">;; define a function to look in a table and</font>
<font color="#008844">;; print out any entries with a function</font>
(defun look-at (table)
(dotimes (ch 127)
(prog ((entry (aref table ch)))
(case entry
(nil nil)
(:constituent nil)
(:white-space nil)
(:sescape nil)
(:mescape nil)
(t (princ (int-char ch))))))
(terpri))
(look-at *readtable*) <font color="#008844">; prints "#'(),;`</font>
</pre>
<p><b>Caution:</b> If you experiment with *readtable*, 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-011.htm#readtable">*readtable*</a>
system variable in the <nobr>XLISP 2.0</nobr> manual.</p>
<p><nobr> <a href="#top">Back to Top</nobr></a></p>
<hr>
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