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<html><head>
<title>XLISP 2.0</title>
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<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="contents.htm">Contents</a> |
<a href="../tutorials/tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
<hr>
<h1>XLISP 2.0</h1>
<hr>
<p><nobr><b>XLISP: An Object-oriented Lisp</b> </nobr> <nobr>Version
2.0</nobr>, <nobr>February 6, 1988</nobr>, by <nobr>David Michael
Betz</nobr>, <nobr>127 Taylor Road</nobr>, Peterborough, <nobr>NH
03458</nobr></p>
<p><nobr>Copyright (c) 1988</nobr>, by <nobr>David Michael Betz</nobr>,
<nobr>All Rights Reserved</nobr>, Permission is granted for unrestricted
<nobr>non-commercial use</nobr>.</p>
<hr>
<ol>
<li><nobr><a href="#introduction">Introduction</a></nobr></li>
<li><nobr><a href="#a-note-from-the-author">A Note From The Author</a></nobr></li>
<li><nobr><a href="#command-loop">Command Loop</a></nobr></li>
<li><nobr><a href="#break-loop">Break Loop</a></nobr></li>
<li><nobr><a href="#data-types">Data Types</a></nobr></li>
<li><nobr><a href="#the-evaluator">The Evaluator</a></nobr></li>
<li><nobr><a href="#lexical-conventions">Lexical Conventions</a></nobr></li>
<li><nobr><a href="#the-readtable">The Readtable</a></nobr></li>
<li><nobr><a href="#lambda-lists">Lambda Lists</a></nobr></li>
<ul>
<li><nobr><a href="#arguments">Arguments</a></nobr></li>
<ul>
<li><nobr><a href="#required-arguments">Required Arguments</a></nobr></li>
<li><nobr><a href="#optional-arguments">Optional Arguments</a></nobr></li>
<li><nobr><a href="#rest-argument">Rest Argument</a></nobr></li>
<li><nobr><a href="#keyword-arguments">Keyword Arguments</a></nobr></li>
<li><nobr><a href="#auxiliary-variables">Auxiliary Variables</a></nobr></li>
</ul>
<li><nobr><a href="#lambda-list-syntax">Lambda List Syntax</a></nobr></li>
</ul>
</ol>
<a name="introduction"></a>
<hr>
<h2>1 Introduction</h2>
<hr>
<p>XLISP is an experimental programming language combining some of the
features of Common Lisp with an object-oriented extension capability. It was
implemented to allow experimentation with object-oriented programming on
small computers. Implementations of XLISP run on virtually every operating
system. XLISP is completely written in the programming language C and is
easily extended with user written built-in functions and classes. It is
available in source form to non-commercial users. Many Common Lisp functions
are built into XLISP. In addition, XLISP defines the objects <a
href="../reference/object.htm">object</a> and <a
href="../reference/class.htm">class</a> as primitives. Object is the
only class that has no superclass and hence is the root of the class
hierarchy tree. Class is the class of which all classes are instances [it is
the only object that is an instance of itself].</p>
<p>This document is a brief description of XLISP. It assumes some knowledge
of LISP and some understanding of the concepts of object-oriented
programming. I recommend the book 'Lisp' by Winston and Horn and published
by Addison Wesley for learning Lisp. The first edition of this book is based
on MacLisp and the second edition is based on Common Lisp. You will probably
also need a copy of 'Common Lisp, The Language' by Guy L. Steele, Jr.,
published by Digital Press to use as a reference for some of the Common Lisp
functions that are described only briefly in this document.</p>
<p>A list with Lisp books and documents available for free in the internet
can be found under <a href="../misc/links.htm">Lisp Links</a>.</p>
<p><nobr> <a href="#top">Back to Top</a></nobr></p>
<a name="a-note-from-the-author"></a>
<hr>
<h2>2 A Note From The Author</h2>
<hr>
<p>If you have any problems with XLISP, feel free to contact me [David Betz]
for help or advice. Please remember that since XLISP is available in source
form in a high level language, many users have been making versions
available on a variety of machines. If you call to report a problem with a
specific version, I may not be able to help you if that version runs on a
machine to which I don't have access. Please have the version number of the
version that you are running readily accessible before calling me.</p>
<p>If you find a bug in XLISP, first try to fix the bug yourself using the
source code provided. If you are successful in fixing the bug, send the bug
report along with the fix to me. If you don't have access to a C compiler or
are unable to fix a bug, please send the bug report to me and I'll try to
fix it.</p>
<p>Any suggestions for improvements will be welcomed. Feel free to extend
the language in whatever way suits your needs. However,</p>
<p><div class="box">
<p><b>PLEASE DO NOT RELEASE ENHANCED VERSIONS WITHOUT CHECKING WITH ME
FIRST!!</b></p>
</div></p>
<p>I would like to be the clearing house for new features added to XLISP. If
you want to add features for your own personal use, go ahead. But, if you
want to distribute your enhanced version, contact me first. Please remember
that the goal of XLISP is to provide a language to learn and experiment with
LISP and object-oriented programming on small computers. I don't want it to
get so big that it requires megabytes of memory to run.</p>
<p>The official XLISP homepage is:</p>
<ul>
<li><a href="http://www.mv.com/ipusers/xlisper/">http://www.mv.com/ipusers/xlisper/</a></li>
</ul>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="command-loop"></a>
<hr>
<h2>3 Command Loop</h2>
<hr>
<p>When XLISP is started, it first tries to load the workspace 'xlisp.wks'
from the current directory. If that file doesn't exist, XLISP builds an
initial workspace, empty except for the built-in functions and symbols. Then
XLISP attempts to load 'init.lsp' from the current directory. It then loads
any files named as parameters on the command line [after appending '.lsp' to
their names].</p>
<p>XLISP then issues the following prompt:</p>
<pre class="example">
>
</pre>
<p>This indicates that XLISP is waiting for an expression to be typed. When
a complete expression has been entered, XLISP attempts to evaluate that
expression. If the expression evaluates successfully, XLISP prints the
result and then returns to the initial prompt waiting for another expression
to be typed.</p>
<a name="interactive-programming"></a>
<p><div class="box">
<p><b>Interactive Programming</b></p>
<p>There are several symbols maintained by the <nobr>read-eval-print</nobr>
loop:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>*</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>the most recent result</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>**</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>the second recent result</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>***</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>the third recent result</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>+</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>the most recent input expression</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>++</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>the second recent input expression</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>+++</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>the third recent input expression</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>−</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">the expression currently being evaluated, becomes the
value of + at the end of the evaluation</td>
</tr>
</tbody></table></p>
<p>These symbols are for interactive programming. <nobr>It is</nobr> not
recommended to use them in program code.</p>
</div></p>
<a name="special-characters"></a>
<p><div class="box">
<p><b>Special Characters</b></p>
<p>When XLISP is running from a console <nobr>[not in</nobr> the Nyquist
<nobr>Java IDE]</nobr>, some control characters invoke operations:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-c</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">executes the <a href="../reference/top-level.htm">top-level</a> function</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-g</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">executes the <a href="../reference/clean-up.htm">clean-up</a> function</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-p</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">executes the <a href="../reference/continue.htm">continue</a> function</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-b</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">stops execution and enters the break command loop,
execution can be continued by typing Control-p <nobr>or
(<a href="../reference/continue.htm">continue</a>)</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-e</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">turns on character echoing [Linux and <nobr>Mac OS X</nobr> only]</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-f</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">turns off character echoing [Linux and <nobr>Mac OS X</nobr> only]</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-t</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">evaluates the <a href="../reference/info.htm">info</a> function</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr>Control-u</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">erases the entire input line</td>
</tr>
</tbody></table></p>
<p>Backspace and Delete characters erase the previous character on the input
line <nobr>[if any]</nobr>.</p>
</div></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="break-loop"></a>
<hr>
<h2>4 Break Loop</h2>
<hr>
<p>When XLISP encounters an error while evaluating an expression, it
attempts to handle the error in the following way:</p>
<dl>
<p><b>1.</b> If the symbol
<a href="../reference/global-breakenable.htm">*breakenable*</a> is true, the
message corresponding to the error is printed. <nobr>If the</nobr> error is
correctable, the correction message is printed.</p>
<dd>
<ul>
<li><p>If the symbol
<a href="../reference/global-tracenable.htm">*tracenable*</a> is true, a
trace back is printed. The number of entries printed depends on the value of
the symbol <a href="../reference/global-tracelimit.htm">*tracelimit*</a>.
<nobr>If this</nobr> symbol is set to something other than a number, the
entire trace back stack is printed.</p></li>
</ul>
<p>XLISP then enters a '<nobr>read-eval-print</nobr>' loop to allow the user
to examine the state of the interpreter in the context of the error. This
loop differs from the normal <nobr>top-level</nobr>
'<nobr>read-eval-print</nobr>' loop in that if the user invokes the
<a href="../reference/continue.htm">continue</a> function:</p>
<pre class="example">
1> (continue)
</pre>
<p>XLISP will continue from a correctable error. <nobr>If the</nobr> user
invokes the <a href="../reference/clean-up.htm">clean-up</a> function:</p>
<pre class="example">
1> (clean-up)
</pre>
<p>XLISP will abort the break loop and return to the top level or the next
lower numbered break loop. When in a break loop, XLISP prefixes the break
level to the normal prompt with a number.</p></dd>
<dt><p><b>2.</b> If the symbol
<a href="../reference/global-breakenable.htm">*breakenable*</a>
is <a href="../reference/nil.htm">NIL</a>, XLISP looks for a surrounding
<a href="../reference/errset.htm">errset</a> function:</p></dt>
</dl>
<ul>
<li type="circle"><p>If an error happened within the scope of an
<a href="../reference/errset.htm">errset</a> function, XLISP examines the
value of the <a href="../reference/errset.htm">errset</a> print flag.
<nobr>If this</nobr> flag is true, the error message is printed.
<nobr>In case</nobr> of an error, the
<a href="../reference/errset.htm">errset</a> function always <nobr>returns
<a href="../reference/nil.htm">NIL</a></nobr>.</p></li>
<li type="circle"><p>If there is no surrounding
<a href="../reference/errset.htm">errset</a> function, XLISP prints the
error message and returns to the top level.</p></li>
</ul>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="data-types"></a>
<hr>
<h2>5 Data Types</h2>
<hr>
<p>There are several different data types available to XLISP
programmers:</p>
<ul>
<li><nobr><a href="../reference/nil.htm">nil</a> - boolean false as well as the empty <a href="../reference/listp.htm">list</a></nobr></li>
<li><nobr><a href="../reference/arrayp.htm">array</a> - including <a href="../reference/hash.htm">hash</a>-tables</nobr></li>
<li><a href="../reference/characterp.htm">character</a></li>
<li><a href="../reference/numberp.htm">number</a></li>
<ul>
<li><a href="../reference/integerp.htm">fixnum</a> - integer number</li>
<li><a href="../reference/floatp.htm">flonum</a> - floating point number</li>
</ul>
<li><nobr><a href="../reference/consp.htm">cons</a> - a non-empty list, where a <a href="../reference/listp.htm">list</a> is of type <a href="../reference/consp.htm">cons</a> or <a href="../reference/nil.htm">nil</a></nobr></li>
<li><a href="../reference/objectp.htm">object</a></li>
<li><a href="../reference/streamp.htm">stream</a></li>
<ul>
<li><nobr><b>file-stream</b> - returned by <a href="../reference/open.htm">open</a></nobr></li>
<li><nobr><b>unnamed-stream</b> - returned by <a href="../reference/make-string-input-stream.htm">make-string-input-stream</a></nobr></li>
</ul>
<li><nobr><a href="../reference/stringp.htm">string</a></nobr></li>
<li><nobr><a href="../reference/symbolp.htm">symbol</a> - including keywords</nobr></li>
<li><nobr><b>subr</b> - built-in function</nobr></li>
<li><nobr><b>fsubr</b> - special form</nobr></li>
<li><nobr><b>closure</b> - user defined function</nobr></li>
<li><nobr><a href="../reference/filep.htm">file</a></nobr></li>
<li><nobr><a href="../reference/soundp.htm">sound</a> - a Nyquist sound</nobr></li>
</ul>
<p>See also the <nobr><a href="../reference/type-of.htm">type-of</a></nobr>
function.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="the-evaluator"></a>
<hr>
<h2>6 The Evaluator</h2>
<hr>
<p>The process of evaluation in XLISP:</p>
<ul>
<li><p>The following Lisp objects evaluate to themselves:</p>
<ul>
<li><nobr><a href="../reference/stringp.htm">string</a></nobr></li>
<li><nobr><a href="../reference/integerp.htm">fixnum</a></nobr></li>
<li><nobr><a href="../reference/characterp.htm">character</a></nobr></li>
<li><nobr><a href="../reference/floatp.htm">flonum</a></nobr></li>
<li><nobr><a href="../reference/objectp.htm">object</a></nobr></li>
<li><nobr><a href="../reference/arrayp.htm">array</a></nobr></li>
<li><nobr><a href="../reference/streamp.htm">stream</a></nobr></li>
<li><nobr><b>subr</b> - built-in function</nobr></li>
<li><nobr><b>fsubr</b> - special form</nobr></li>
<li><nobr><b>closure</b> - user defined function</nobr></li>
</ul>
</li>
<li><p><font color="#000088"><b>Symbols</b></font> act as variables and are
evaluated by retrieving the value associated with their current
binding.</p></li>
<li><p><font color="#000088"><b>Lists</b></font> are evaluated by examining
the first element of the list and then taking one of the following
actions:</p></li>
<ul>
<li><p>If it is a <font color="#000088"><b>symbol</b></font>, the functional
binding of the symbol is retrieved.</p></li>
<li><p>If it is a <font color="#000088"><b>lambda expression</b></font>, a
closure is constructed for the function described by the lambda
expression.</p></li>
<li><p>If it is a <font color="#000088"><b>subr</b></font> [built-in
function], <font color="#000088"><b>fsubr</b></font> [special form] or <font
color="#000088"><b>closure</b></font> [user defined function], it stands for
itself.</p></li>
<li><p>Any other value is an <font color="#AA0000"><b>error</b></font>.</p></li>
</ul>
<p>Then, the value produced by the previous step is examined:</p>
<ul>
<li><p>If it is a <font color="#000088"><b>subr</b></font>
<nobr>[built-in</nobr> function] or <font
color="#000088"><b>closure</b></font> [user defined function], the remaining
list elements are evaluated and the subr or closure is called with these
evaluated expressions as arguments.</p></li>
<li><p>If it is an <font color="#000088"><b>fsubr</b></font> [special form],
the fsubr is called using the remaining list elements as arguments
[unevaluated].</p></li>
<li><p>If it is a<font color="#000088"><b> macro</b></font>, the macro is
expanded using the remaining list elements as arguments [unevaluated]. The
macro expansion is then evaluated in place of the original macro
call.</p></li>
</ul>
</ul>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="lexical-conventions"></a>
<hr>
<h2>7 Lexical Conventions</h2>
<hr>
<p>The following conventions must be followed when entering XLISP
programs:</p>
<ul>
<li><p>Comments in XLISP code begin with a semicolon character and continue
to the end of the line.</p></li>
<li><p>Symbol names in XLISP can consist of any sequence of non-blank
printable characters except the following:</p></li>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>(</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>opening parenthesis</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>)</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>closing parenthesis</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>'</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>single-quote</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>`</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>backquote</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>,</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>comma</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>"</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>double-quote</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr>;</nobr></td>
<td><nobr> - </nobr></td>
<td width="100%"><nobr>semicolon</nobr></td>
</tr>
</tbody></table></p>
<li><p>Uppercase and lowercase characters are not distinguished within
symbol names. All lowercase characters are mapped to uppercase on
input.</p></li>
<li><p>Integer literals consist of a sequence of digits optionally beginning
with a '+' [plus] or '-' [minus]. The range of values an integer can
represent is limited by the size of a C 'long' value on the machine on which
XLISP is running. <nobr>Also be</nobr> aware that Nyquist doesn't check for
CPU register overflow with integer numbers, so for example if you add 1 to
the biggest Nyquist integer number, the result will be a negative
number.</p></li>
<li><p>Floating point literals consist of a sequence of digits optionally
beginning with a '+' [plus] or '-' [minus] and including an embedded decimal
point. The range of values a floating point number can represent is limited
by the size of a C 'float' [or 'double' on machines with 32 bit addresses]
on the machine on which XLISP is running.</p></li>
<li><p>Literal strings are sequences of characters surrounded by double
quotes. Within quoted strings the '\' [backslash] character is used to allow
non-printable characters to be included. The codes recognized are:</p></li>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>\\</code></nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">the character '\' [backslash]</td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>\n</code></nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">newline</td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>\t</code></nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">tab</td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>\r</code></nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">return</td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>\f</code></nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">form feed</td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>\<font color="#0000CC">nnn</font></code></nobr></td>
<td><nobr> - </nobr></td>
<td width="100%">the character whose octal code is 'nnn'</td>
</tr>
</tbody></table></p>
<p>An <a href="../misc/ascii-table.htm">ASCII</a> table
is provided with this version of the XLISP manual with all octal, decimal
and hexadecimal character values.</p>
</ul>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="the-readtable"></a>
<hr>
<h2>8 The Readtable</h2>
<hr>
<a name="constituent"></a><a name="white-space"></a>
<a name="tmacro"></a><a name="nmacro"></a>
<a name="sescape"></a><a name="mescape"></a>
<p>The behavior of the reader is controlled by a data structure called a
'readtable'. The reader uses the symbol
<a href="../reference/global-readtable.htm">*readtable*</a> to locate the
current readtable. This table controls the interpretation of input
characters. It is an array with 128 entries, one for each of the
<a href="../misc/ascii-table.htm">ASCII</a> character codes. Each
entry contains one of the following things:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code> NIL</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>indicating an invalid character</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/nil.htm">nil</a>]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>:CONSTITUENT</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>indicating a symbol constituent</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/keyword-constituent.htm">:constituent</a>]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>:WHITE-SPACE</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>indicating a whitespace character</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/keyword-white-space.htm">:white-space</a>]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>(:TMACRO . <font color="#0000CC">function</font>)</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>terminating readmacro</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/keyword-tmacro.htm">:tmacro</a>]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>(:NMACRO . <font color="#0000CC">function</font>)</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>non-terminating readmacro</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/keyword-nmacro.htm">:nmacro</a>]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>:SESCAPE</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>single escape character '\'</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/keyword-sescape.htm">:sescape</a>]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>:MESCAPE</code></nobr></td>
<td><nobr> - </nobr></td>
<td><nobr>multiple escape character '|'</nobr></td>
<td width="100%"><nobr> [see
<a href="../reference/keyword-mescape.htm">:mescape</a>]</nobr></td>
</tr>
</tbody></table></p>
<p>In the case of <a href="../reference/keyword-tmacro.htm">:tmacro</a> and
<a href="../reference/keyword-nmacro.htm">:nmacro</a>, the 'fun' component
is a function. This can either be a built-in readmacro function or a
<a href="../reference/lambda.htm">lambda</a> expression. The
function should take two parameters. The first is the input stream and the
second is the character that caused the invocation of the readmacro. The
readmacro function should return
<a href="../reference/nil.htm">NIL</a> to indicate that the
character should be treated as white space or a value
<a href="../reference/cons.htm">cons</a>ed with
<a href="../reference/nil.htm">NIL</a> to indicate that the
readmacro should be treated as an occurence of the specified value. Of
course, the readmacro code is free to
<a href="../reference/read.htm">read</a> additional characters
from the input stream.</p>
<a name="quote"></a><a name="function"></a><a name="array"></a>
<a name="hexadecimal"></a><a name="octal"></a><a name="binary"></a>
<a name="character"></a><a name="comment"></a><a name="uninterned"></a>
<a name="backquote"></a><a name="comma"></a><a name="comma-at"></a>
<p>XLISP defines several useful read macros:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>'<font color="#0000CC">expression</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>(<a href="../reference/quote.htm">quote</a>
<i>expr</i>)</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#'<font color="#0000CC">expression</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>(<a href="../reference/function.htm">function</a>
<i>expr</i>)</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#(<font color="#0000CC">expression</font><font color="#008844">...</font>)</code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>an array of the specified expressions</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#x<font color="#0000CC">digits</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>a hexadecimal number [0-9,A-F]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#o<font color="#0000CC">digits</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>an octal number [0-7]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#b<font color="#0000CC">digits</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>a binary number [0-1]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#\<font color="#0000CC">character</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>a single character</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#| <font color="#008844">...</font> |#</code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>a comment</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#:<font color="#0000CC">symbol</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>an uninterned symbol</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>`<font color="#0000CC">expression</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>(<a href="../reference/backquote.htm">backquote</a>
<i>expr</i>)</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>,<font color="#0000CC">expression</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>(<a href="../reference/backquote.htm">comma</a>
<i>expr</i>)</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>,@<font color="#0000CC">expression</font></code></nobr></td>
<td><nobr> = </nobr></td>
<td width="100%"><nobr>(<a href="../reference/backquote.htm">comma-at</a>
<i>expr</i>)</nobr></td>
</tr>
</tbody></table></p>
<a name="Tab"></a><a name="Newline"></a><a name="Space"></a>
<p>Characters names handled by the reader:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#\Tab</code></nobr></td>
<td><nobr> = </nobr></td>
<td><nobr>horiz. tab</nobr></td>
<td><nobr> [<a href="../misc/ascii-table.htm">ASCII</a> decimal value 9]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#\Newline</code></nobr></td>
<td><nobr> = </nobr></td>
<td><nobr>newline</nobr></td>
<td><nobr> [<a href="../misc/ascii-table.htm">ASCII</a> decimal value 10]</nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>#\Space</code></nobr></td>
<td><nobr> = </nobr></td>
<td><nobr>space</nobr></td>
<td><nobr> [<a href="../misc/ascii-table.htm">ASCII</a> decimal value 32]</nobr></td>
</tr>
</tbody></table></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="lambda-lists"></a>
<hr>
<h2>9 Lambda Lists</h2>
<a name="arguments"></a>
<hr>
<h2>9.1 Arguments</h2>
<hr>
<p>There are several forms in XLISP that require that a <nobr>'lambda
list'</nobr> be specified. A lambda list is a definition of the arguments
accepted by a function.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="required-arguments"></a>
<hr>
<h2>9.1.1 Required Arguments</h2>
<hr>
<p>The lambda list starts with 'required' arguments. Required arguments must
be specified in every call to the function.</p>
<p>The function '<nobr>print-x</nobr>' has exactly one required
<nobr>argument 'x'</nobr>:</p>
<pre class="example">
(defun print-x (x)
(print x))
(print-x 1) => 1
(print-x) => <font color="#AA0000">error: too few arguments</font>
(print-x 1 2) => <font color="#AA0000">error: too many arguments</font>
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="optional-arguments"></a>
<hr>
<h2>9.1.2 Optional Arguments</h2>
<hr>
<p>The <nobr><a href="#required-arguments">Required Arguments</a></nobr> are followed by
the <a href="../reference/lambda-keyword-optional.htm">&optional</a>
arguments. Optional arguments may be provided or omitted in a call. An
initialization expression may be specified to provide a default value for an
<a href="../reference/lambda-keyword-optional.htm">&optional</a>
argument if it is omitted from a call. If no initialization expression is
specified, an omitted argument is initialized to
<a href="../reference/nil.htm">NIL</a>.</p>
<p>It is also possible to provide the name of a 'supplied-p' variable that
can be used to determine if a call provided a value for the argument or if
the initialization expression was used. If specified, the 'supplied-p'
variable will be bound to
<a href="../reference/t.htm"> T </a> if a value was
specified in the call and
<a href="../reference/nil.htm">NIL</a> if the default value was
used.</p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="rest-argument"></a>
<hr>
<h2>9.1.3 Rest Argument</h2>
<hr>
<p>The <nobr><a href="#optional-arguments">Optional Arguments</a></nobr> are followed by
the <a href="../reference/lambda-keyword-rest.htm">&rest</a> argument.
<nobr>The <a href="../reference/lambda-keyword-rest.htm">&rest</a></nobr>
argument gets bound to the remainder of the argument list after the required
and <a href="../reference/lambda-keyword-optional.htm">&optional</a>
arguments have been removed.</p>
<p><div class="box">
<p><b>Known Problems with the Rest Argument</b></p>
<p>A subtle problem arises if
<nobr><a href="#optional-arguments">Optional Arguments</a></nobr> are used together with
a <a href="../reference/lambda-keyword-rest.htm">&rest</a> argument:</p>
<pre class="example">
(defun test (&optional opt &rest rest)
(format t "opt = ~a, rest = ~a~%" opt rest))
(test 1) => opt = 1, rest = NIL
(test 1 2) => opt = 1, rest = (2)
(test 1 2 3) => opt = 1, rest = (2 3)
</pre>
<p>Now the
<a href="../reference/lambda-keyword-optional.htm">&optional</a>
argument is not optional anymore, there is no way to make the first argument
appear in the <a href="../reference/lambda-keyword-rest.htm">&rest</a>
list and not in the
<a href="../reference/lambda-keyword-optional.htm">&optional</a>
variable. This is not a XLISP bug, this is a general Lisp phenomenon.
<nobr>In Lisp</nobr> it's not a good idea to use
<nobr><a href="#optional-arguments">Optional Arguments</a></nobr> together with a
<a href="../reference/lambda-keyword-rest.htm">&rest</a> argument.</p>
<p>If a <a href="../reference/lambda-keyword-rest.htm">&rest</a>
argument is used togethter with
<nobr><a href="#keyword-arguments">Keyword Arguments</a></nobr>, then the keywords and
their arguments appear in the list bound to the
<a href="../reference/lambda-keyword-rest.htm">&rest</a></nobr>
argument. This is not neccessarily a XLISP bug, this also happens with
other Lisps. <nobr>In Lisp</nobr> it's also not a good idea to use
<nobr><a href="#keyword-arguments">Keyword Arguments</a></nobr> together with a
<a href="../reference/lambda-keyword-rest.htm">&rest</a> argument.</p>
<p><b>XLISP Bug:</b> <nobr>If the</nobr> number of elements in a
<a href="../reference/lambda-keyword-rest.htm">&rest</a> list
is odd, then <a href="../reference/lambda-keyword-key.htm">&key</a>
variables have wrong values:</p>
<pre class="example">
(defun test (&rest rest &key (key t))
(format t "rest = ~a, key = ~a~%" rest key))
(test 1 :key 'a) => rest = (1 :KEY A), key = T <font color="#AA0000">; wrong KEY value</font>
(test 1 2 :key 'a) => rest = (1 2 :KEY A), key = A <font color="#008844">; quirk, but correct KEY value</font>
(test 1 2 3 :key 'a)) => rest = (1 2 3 :KEY A), key = T <font color="#AA0000">; again wrong KEY value</font>
</pre>
</div></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="keyword-arguments"></a>
<hr>
<h2>9.1.4 Keyword Arguments</h2>
<hr>
<p>The <nobr><a href="#rest-argument">Rest Argument</a></nobr> is
followed by the <a href="../reference/lambda-keyword-key.htm">&key</a>
arguments. When a keyword argument is passed to a function, a pair of values
appears in the argument list. The first expression in the pair should
evaluate to a keyword symbol [a symbol that begins with a <nobr>colon
':'].</nobr> The value of the second expression is the value of the keyword
argument.</p>
<p>Like <a href="../reference/lambda-keyword-optional.htm">&optional</a>
arguments, <a href="../reference/lambda-keyword-key.htm">&key</a> arguments can
have initialization expressions and 'supplied-p' variables. In addition, it
is possible to specify the keyword to be used in a function call. If no
keyword is specified, the keyword obtained by adding a colon ':' to the
beginning of the keyword argument symbol is used.</p>
<p>In other words, if the keyword argument symbol is:</p>
<pre class="example">
foo
</pre>
<p>the keyword will be:</p>
<pre class="example">
:foo
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="auxiliary-variables"></a>
<hr>
<h2>9.1.5 Auxiliary Variables</h2>
<hr>
<p>The <nobr><a href="#keyword-arguments">Keyword Arguments</a></nobr> are followed by
the <a href="../reference/lambda-keyword-aux.htm">&aux</a> variables.
These are local variables that are bound during the evaluation of the
function body. It is possible to have initialization expressions for the
<a href="../reference/lambda-keyword-aux.htm">&aux</a> variables.</p>
<p><nobr> <a href="#top">Back to Top</a></nobr></p>
<a name="lambda-list-syntax"></a>
<hr>
<h2>9.2 Lambda List Syntax</h2>
<hr>
<p>Here is the complete syntax for lambda lists:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td width="100%" colspan="2"><nobr>(<i>required-arg</i> ...</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr><code> </code></nobr></td>
<td width="100%"><nobr>[<b>&optional</b> [<i>optional-arg</i> | (<i>optional-arg</i> [<i>init-form</i> [<i>supplied-var</i>]])] ... ]</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr><code> </code></nobr></td>
<td width="100%"><nobr>[<b>&rest</b> <i>rest-arg</i>]</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr><code> </code></nobr></td>
<td width="100%"><nobr>[<b>&key</b> [<i>key-arg</i> | ([<i>key-arg</i> | (<i>keyword</i> <i>key-arg</i>)] [<i>init-form</i> [<i>supplied-var</i>]]) ...] <b>&allow-other-keys</b>]</nobr></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td><nobr><code> </code></nobr></td>
<td width="100%"><nobr>[<b>&aux</b> [<i>aux-var</i> | (<i>aux-var</i> [<i>init-form</i>])] ... ])</nobr></td>
</tr>
</tbody></table></p>
<p>where:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>required-arg</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is a <a href="#required-arguments">required</a> argument symbol</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>optional-arg</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is an <a href="#optional-arguments">&optional</a> argument symbol</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>rest-arg</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is the <a href="#rest-argument">&rest</a> argument symbol</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>key-arg</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is a <a href="#keyword-arguments">&key</a> argument symbol</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>keyword</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is a <a href="#keyword-arguments">keyword</a> symbol</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>aux-var</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is an <a href="#auxiliary-variables">auxiliary</a> variable symbol</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>init-form</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is an initialization expression</td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td align="right"><nobr><i>supplied-var</i></nobr></td>
<td><nobr> — </nobr></td>
<td width="100%">is a supplied-p variable symbol</td>
</tr>
</tbody></table></p>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<hr>
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