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
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
|
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN" "http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>SWI-Prolog 7.3.6 Reference Manual: Section 4.30</title><link rel="home" href="index.html">
<link rel="contents" href="Contents.html">
<link rel="index" href="DocIndex.html">
<link rel="summary" href="summary.html">
<link rel="previous" href="allsolutions.html">
<link rel="next" href="format.html">
<style type="text/css">
/* Style sheet for SWI-Prolog latex2html
*/
dd.defbody
{ margin-bottom: 1em;
}
dt.pubdef, dt.multidef
{ color: #fff;
padding: 2px 10px 0px 10px;
margin-bottom: 5px;
font-size: 18px;
vertical-align: middle;
overflow: hidden;
}
dt.pubdef { background-color: #0c3d6e; }
dt.multidef { background-color: #ef9439; }
.bib dd
{ margin-bottom: 1em;
}
.bib dt
{ float: left;
margin-right: 1.3ex;
}
pre.code
{ margin-left: 1.5em;
margin-right: 1.5em;
border: 1px dotted;
padding-top: 5px;
padding-left: 5px;
padding-bottom: 5px;
background-color: #f8f8f8;
}
div.navigate
{ text-align: center;
background-color: #f0f0f0;
border: 1px dotted;
padding: 5px;
}
div.title
{ text-align: center;
padding-bottom: 1em;
font-size: 200%;
font-weight: bold;
}
div.author
{ text-align: center;
font-style: italic;
}
div.abstract
{ margin-top: 2em;
background-color: #f0f0f0;
border: 1px dotted;
padding: 5px;
margin-left: 10%; margin-right:10%;
}
div.abstract-title
{ text-align: center;
padding: 5px;
font-size: 120%;
font-weight: bold;
}
div.toc-h1
{ font-size: 200%;
font-weight: bold;
}
div.toc-h2
{ font-size: 120%;
font-weight: bold;
margin-left: 2em;
}
div.toc-h3
{ font-size: 100%;
font-weight: bold;
margin-left: 4em;
}
div.toc-h4
{ font-size: 100%;
margin-left: 6em;
}
span.sec-nr
{
}
span.sec-title
{
}
span.pred-ext
{ font-weight: bold;
}
span.pred-tag
{ float: right;
padding-top: 0.2em;
font-size: 80%;
font-style: italic;
color: #fff;
}
div.caption
{ width: 80%;
margin: auto;
text-align:center;
}
/* Footnotes */
.fn {
color: red;
font-size: 70%;
}
.fn-text, .fnp {
position: absolute;
top: auto;
left: 10%;
border: 1px solid #000;
box-shadow: 5px 5px 5px #888;
display: none;
background: #fff;
color: #000;
margin-top: 25px;
padding: 8px 12px;
font-size: larger;
}
sup:hover span.fn-text
{ display: block;
}
/* Lists */
dl.latex
{ margin-top: 1ex;
margin-bottom: 0.5ex;
}
dl.latex dl.latex dd.defbody
{ margin-bottom: 0.5ex;
}
/* PlDoc Tags */
dl.tags
{ font-size: 90%;
margin-left: 5ex;
margin-top: 1ex;
margin-bottom: 0.5ex;
}
dl.tags dt
{ margin-left: 0pt;
font-weight: bold;
}
dl.tags dd
{ margin-left: 3ex;
}
td.param
{ font-style: italic;
font-weight: bold;
}
/* Index */
dt.index-sep
{ font-weight: bold;
font-size: +1;
margin-top: 1ex;
}
/* Tables */
table.center
{ margin: auto;
}
table.latex
{ border-collapse:collapse;
}
table.latex tr
{ vertical-align: text-top;
}
table.latex td,th
{ padding: 2px 1em;
}
table.latex tr.hline td,th
{ border-top: 1px solid black;
}
table.frame-box
{ border: 2px solid black;
}
</style>
</head>
<body style="background:white">
<div class="navigate"><a class="nav" href="index.html"><img src="home.gif" alt="Home"></a>
<a class="nav" href="Contents.html"><img src="index.gif" alt="Contents"></a>
<a class="nav" href="DocIndex.html"><img src="yellow_pages.gif" alt="Index"></a>
<a class="nav" href="summary.html"><img src="info.gif" alt="Summary"></a>
<a class="nav" href="allsolutions.html"><img src="prev.gif" alt="Previous"></a>
<a class="nav" href="format.html"><img src="next.gif" alt="Next"></a>
</div>
<h2 id="sec:forall2"><a id="sec:4.30"><span class="sec-nr">4.30</span> <span class="sec-title">Forall</span></a></h2>
<a id="sec:forall2"></a>
<dl class="latex">
<dt class="pubdef"><span class="pred-tag">[semidet]</span><a id="forall/2"><strong>forall</strong>(<var>:Cond,
:Action</var>)</a></dt>
<dd class="defbody">
For all alternative bindings of <var>Cond</var>, <var>Action</var> can
be proven. The example verifies that all arithmetic statements in the
given list are correct. It does not say which is wrong if one proves
wrong.
<pre class="code">
?- forall(member(Result = Formula, [2 = 1 + 1, 4 = 2 * 2]),
Result =:= Formula).
</pre>
<p>The predicate <a id="idx:forall2:1255"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
is implemented as <code>\+ ( Cond, \+ Action)</code>, i.e., <i>There is
no instantiation of <var>Cond</var> for which <var>Action</var> is
false.</i>. The use of double negation implies that
<a id="idx:forall2:1256"></a><a class="pred" href="forall2.html#forall/2">forall/2</a> <em>does
not change any variable bindings</em>. It proves a relation. The <a id="idx:forall2:1257"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
control structure can be used for its side-effects. E.g., the following
asserts relations in a list into the dynamic database:
<pre class="code">
?- forall(member(Child-Parent, ChildPairs),
assertz(child_of(Child, Parent))).
</pre>
<p>Using <a id="idx:forall2:1258"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
as <code>forall(Generator, SideEffect)</code> is preferred over the
classical <em>failure driven loop</em> as shown below because it makes
it explicit which part of the construct is the generator and which part
creates the side effects. Also, unexpected failure of the side effect
causes the construct to fail. Failure makes it evident that there is an
issue with the code, while a failure driven loop would succeed with an
erroneous result.
<pre class="code">
...,
( Generator,
SideEffect,
fail
; true
)
</pre>
<p>If your intent is to create variable bindings, the <a id="idx:forall2:1259"></a><a class="pred" href="forall2.html#forall/2">forall/2</a>
control structure is inadequate. Possibly you are looking for <a id="idx:maplist2:1260"></a><a class="pred" href="apply.html#maplist/2">maplist/2</a>,
<a id="idx:findall3:1261"></a><a class="pred" href="allsolutions.html#findall/3">findall/3</a>
or <a id="idx:foreach2:1262"></a><a class="pred" href="aggregate.html#foreach/2">foreach/2</a>.
</dd>
</dl>
<p></body></html>
|
