1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
|
<html><head>
<title>Lisp FAQ</title>
<style type="text/css">
.example {
color: #000000;
background-color: #F5F5F5;
padding: 8px;
border: #808080;
border-style: solid;
border-width: 1px;
width:auto;
}
.button {
color: #000000;
background-color: #F5F5F5;
padding-top: 1px;
padding-bottom: 1px;
padding-left: 4px;
padding-right: 8px;
border: #808080;
border-style: solid;
border-width: 1px;
white-space: pre;
}
.box {
color: #000000;
padding-top: 4px;
padding-bottom: 4px;
padding-left: 16px;
padding-right: 16px;
border: #808080;
border-style: solid;
border-width: 1px;
}
</style>
</head>
<body>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
<hr>
<h1>Lisp FAQ</h1>
<hr>
<ol>
<li><nobr><a href="#and-or-with-apply-funcall">Why do #'and and #'or not work with apply and funcall?</a></nobr></li>
<li><nobr><a href="#more-faqs">Where can I find more Lisp FAQs in the Internet?</a></nobr></li>
</ol>
<a name="and-or-with-apply-funcall"></a>
<hr>
<h2>Why do #'and and #'or not work with apply and funcall?</h2>
<hr>
<p><nobr>From
<a href="http://www.cs.cmu.edu/Groups/AI/html/faqs/lang/lisp/part3/faq-doc-3.html"
>http://www.cs.cmu.edu/Groups/AI/html/faqs/lang/lisp/part3/faq-doc-3.html</a></nobr></p>
<p>The short answer is that <a href="../reference/and.htm">and</a> and
<a href="../reference/or.htm">or</a> are special operators, not functions,
while <a href="../reference/apply.htm">apply</a> and
<a href="../reference/funcall.htm">funcall</a> can only be used to invoke
functions, not macros and special operators.</p>
<p>The reason why <a href="../reference/and.htm">and</a> and <a
href="../reference/or.htm">or</a> are special operators is because they
implement control structure in addition to computing a boolean value. They
evaluate their subforms sequentially from left to right, and stop evaluating
subforms as soon as the result can be determined. This is referred to as
'<nobr>short circuiting</nobr>'. <a href="../reference/apply.htm">apply</a>
and <a href="../reference/funcall.htm">funcall</a>, however, are ordinary
functions. Therefore, their arguments are evaluated before they are called.
Thus, were <a href="../reference/apply.htm">apply</a> able to be used with
#'<a href="../reference/and.htm">and</a> and
<a href="../reference/or.htm">or</a>, the <nobr>short-circuiting</nobr>
would be defeated.</p>
<p>Perhaps you don't really care about the <nobr>short-circuiting</nobr>,
and simply want the functional, boolean interpretation. While this may be a
reasonable interpretation of trying to
<a href="../reference/apply.htm">apply</a>
<a href="../reference/and.htm">and</a>
<nobr>or <a href="../reference/or.htm">or</a></nobr>, it doesn't generalize
to other macros well, so there's no obvious way to have the Lisp system 'do
the right thing' when trying to apply macros. <nobr>The only</nobr> function
associated with a macro is its expander function. This function accepts and
returns and form, so it cannot be used to compute the value.</p>
<p>The <nobr>Common Lisp</nobr> functions EVERY, SOME and IDENTITY can be
used to get the functionality you intend when trying to
<a href="../reference/apply.htm">apply</a>
#'<a href="../reference/and.htm">and</a>
<nobr>and #'<a href="../reference/or.htm">or</a></nobr>:</p>
<p><table cellpadding="0" cellspacing="0"><tbody>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>(apply #'and <font color="#0000CC">list</font>)</code></nobr></td>
<td><nobr> → </nobr></td>
<td class="button"><nobr><code>(every #'identity <font color="#0000CC">list</font>)</code></nobr></td>
</tr>
<tr>
<td height="2px"></td>
</tr>
<tr>
<td><nobr><code> </code></nobr></td>
<td class="button"><nobr><code>(apply #'or <font color="#0000CC">list</font>)</code></nobr></td>
<td><nobr> → </nobr></td>
<td class="button"><nobr><code>(some #'identity <font color="#0000CC">list</font>)</code></nobr></td>
</tr>
</tbody></table></p>
<p>Defining <a href="../reference/and.htm">and</a> and
<a href="../reference/or.htm">or</a> as functions using
<a href="../reference/cons.htm">cons</a> and
<a href="../reference/eval.htm">eval</a>:</p>
<pre class="example">
(defun <font color="#0000CC">and-fn</font> (&rest args)
(eval (cons 'and args)))
(defun <font color="#0000CC">or-fn</font> (&rest args)
(eval (cons 'or args)))
</pre>
<p>Defining <a href="../reference/and.htm">and</a> and
<a href="../reference/or.htm">or</a> as functions using
<a href="../reference/dolist.htm">dolist</a>:</p>
<pre class="example">
(defun <font color="#0000CC">and-fn</font> (&rest args)
(dolist (x args t)
(and (not x) (return nil))))
(defun <font color="#0000CC">or-fn</font> (&rest args)
(dolist (x args nil)
(and x (return t))))
</pre>
<pre class="example">
(defun <font color="#0000CC">apply*</font> (function args)
(if (eq (type-of function) 'fsubr)
(eval (cons function args))
(apply function args)))
</pre>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<a name="more-faqs"></a>
<hr>
<h2>Where can I find more Lisp FAQs in the Internet?</h2>
<hr>
<ul>
<li><nobr><a href="http://www.cs.cmu.edu/Groups/AI/html/faqs/lang/lisp/top.html"
>http://www.cs.cmu.edu/Groups/AI/html/faqs/lang/lisp/top.html</a>
- comp.lang.lisp FAQ from the CMU AI Repository</nobr></li>
</ul>
<p><nobr> <a href="#top">Back to top</a></nobr></p>
<hr>
<a href="../start.htm">Nyquist / XLISP 2.0</a> -
<a href="../manual/contents.htm">Contents</a> |
<a href="tutorials.htm">Tutorials</a> |
<a href="../examples/examples.htm">Examples</a> |
<a href="../reference/reference-index.htm">Reference</a>
</body></html>
|
