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
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
|
<!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 4.24</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="chartype.html">
<link rel="next" href="charconv.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="chartype.html"><img src="prev.gif" alt="Previous"></a>
<a class="nav" href="charconv.html"><img src="next.gif" alt="Next"></a>
</div>
<h2 id="sec:operators"><a id="sec:4.24"><span class="sec-nr">4.24</span> <span class="sec-title">Operators</span></a></h2>
<a id="sec:operators"></a>
<p>Operators are defined to improve the readability of source code. For
example, without operators, to write <code>2*3+4*5</code> one would have
to write <code>+(*(2,3),*(4,5))</code>. In Prolog, a number of operators
have been predefined. All operators, except for the comma (,) can be
redefined by the user.
<p><a id="idx:operatorandmodules:1195"></a>Some care has to be taken
before defining new operators. Defining too many operators might make
your source `natural' looking, but at the same time make it hard to
understand the limits of your syntax. To ease the pain, as of SWI-Prolog
3.3.0, operators are local to the module in which they are defined.
Operators can be exported from modules using a term
<code>op(Precedence, Type, Name)</code> in the export list as specified
by
<a id="idx:module2:1196"></a><a class="pred" href="defmodule.html#module/2">module/2</a>.
Many modern Prolog systems have module specific operators.
Unfortunately, there is no established interface for exporting and
importing operators. SWI-Prolog's convention has been addopted by YAP.
<p>The module table of the module <code>user</code> acts as default
table for all modules and can be modified explicitly from inside a
module to achieve compatibility with other Prolog that do not have
module-local operators:
<pre class="code">
:- module(prove,
[ prove/1
]).
:- op(900, xfx, user:(=>)).
</pre>
<p>In SWI-Prolog, a <em>quoted atom</em> never acts as an operator. Note
that the portable way to stop an atom acting as an operator is to
enclose it in parentheses like this: (myop). See also
<a class="sec" href="ext-syntax.html">section 5.3.1</a>.
<dl class="latex">
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="op/3"><strong>op</strong>(<var>+Precedence,
+Type, :Name</var>)</a></dt>
<dd class="defbody">
Declare <var>Name</var> to be an operator of type <var>Type</var> with
precedence
<var>Precedence</var>. <var>Name</var> can also be a list of names, in
which case all elements of the list are declared to be identical
operators.
<var>Precedence</var> is an integer between 0 and 1200. Precedence 0
removes the declaration. <var>Type</var> is one of: <code>xf</code>, <code>yf</code>,
<code>xfx</code>, <code>xfy</code>, <code>yfx</code>, <code>fy</code> or
<code>fx</code>. The `<code>f</code>' indicates the position of the
functor, while
<code>x</code> and <code>y</code> indicate the position of the
arguments. `<code>y</code>' should be interpreted as ``on this position
a term with precedence lower or equal to the precedence of the functor
should occur''. For `<code>x</code>' the precedence of the argument must
be strictly lower. The precedence of a term is 0, unless its principal
functor is an operator, in which case the precedence is the precedence
of this operator. A term enclosed in parentheses <code>( ... )</code>
has precedence 0.
<p>The predefined operators are shown in <a class="tab" href="operators.html#tab:operators">table
5</a>. Operators can be redefined, unless prohibited by one of the
limitations below. Applications must be careful with (re-)defining
operators because changing operators may cause (other) files to be
interpreted
<b>differently</b>. Often this will lead to a syntax error. In other
cases, text is read silently into a different term which may lead to
subtle and difficult to track errors.
<p>
<ul class="latex">
<li>It is not allowed to redefine the comma (<code>','</code>).
<li>The bar (<code>|</code>) can only be (re-)defined as infix operator
with priority not less than 1001.
<li>It is not allowed to define the empty list (<code>[]</code>) or the
curly-bracket pair (<code>{}</code>) as operators.
</ul>
<p>In SWI-Prolog, operators are <em>local</em> to a module (see also
<a class="sec" href="moduleop.html">section 6.8</a>). Keeping operators
in modules and using controlled import/export of operators as described
with the <a id="idx:module2:1197"></a><a class="pred" href="defmodule.html#module/2">module/2</a>
directive keep the issues manageable. The module <code>system</code>
provides the operators from <a class="tab" href="operators.html#tab:operators">table
5</a> and these operators cannot be modified. Files that are loaded from
the SWI-Prolog directories resolve operators and predicates from this <code>system</code>
module rather than <code>user</code>, which makes the semantics of the
library and development system modules independent of operator changes
to the <code>user</code> module.
<p><table class="latex frame-box center">
<tr><td align=right>1200</td><td>xfx</td><td><strong><code>--></code></strong>, <strong><code>:-</code></strong> </td></tr>
<tr><td align=right>1200</td><td>fx</td><td><strong><code>:-</code></strong>, <strong><code>?-</code></strong> </td></tr>
<tr><td align=right>1150</td><td>fx</td><td><strong>dynamic</strong>, <strong>discontiguous</strong>, <strong>initialization</strong>,
<strong>meta_predicate</strong>,
<strong>module_transparent</strong>, <strong>multifile</strong>, <strong>public</strong>,
<strong>thread_local</strong>, <strong>thread_initialization</strong>, <strong>volatile</strong> </td></tr>
<tr><td align=right>1100</td><td>xfy</td><td><strong><code>;</code></strong>, <strong><code>|</code></strong> </td></tr>
<tr><td align=right>1050</td><td>xfy</td><td><strong><code>-></code></strong>, <strong><code>*-></code></strong> </td></tr>
<tr><td align=right>1000</td><td>xfy</td><td><strong><code>,</code></strong> </td></tr>
<tr><td align=right>990</td><td>xfx</td><td><strong>:=</strong> </td></tr>
<tr><td align=right>900</td><td>fy</td><td><strong><code>\+</code></strong> </td></tr>
<tr><td align=right>700</td><td>xfx</td><td><strong><code><</code></strong>, <strong><code>=</code></strong>, <strong><code>=..</code></strong>, <strong><code>=@=</code></strong>, <strong><code>\=@=</code></strong>,
<strong><code>=:=</code></strong>, <strong><code>=<</code></strong>, <strong><code>==</code></strong>,
<strong><code>=\=</code></strong>, <strong><code>></code></strong>, <strong><code>>=</code></strong>, <strong><code>@<</code></strong>, <strong><code>@=<</code></strong>, <strong><code>@></code></strong>,
<strong><code>@>=</code></strong>, <strong><code>\=</code></strong>, <strong><code>\==</code></strong>, <strong>as</strong>, <strong>is</strong>,
<strong><code>>:<</code></strong>, <strong><code>:<</code></strong>
</td></tr>
<tr><td align=right>600</td><td>xfy</td><td><strong><code>:</code></strong> </td></tr>
<tr><td align=right>500</td><td>yfx</td><td><strong><code>+</code></strong>, <strong><code>-</code></strong>, <strong><code>/\</code></strong>, <strong><code>\/</code></strong>, <strong>xor</strong> </td></tr>
<tr><td align=right>500</td><td>fx</td><td><strong><code>?</code></strong> </td></tr>
<tr><td align=right>400</td><td>yfx</td><td><strong><code>*</code></strong>, <strong><code>/</code></strong>, <strong><code>//</code></strong>, <strong>div</strong>, <strong>rdiv</strong>,
<strong><code><<</code></strong>, <strong><code>>></code></strong>, <strong>mod</strong>, <strong>rem</strong> </td></tr>
<tr><td align=right>200</td><td>xfx</td><td><strong><code>**</code></strong> </td></tr>
<tr><td align=right>200</td><td>xfy</td><td><strong><code>^</code></strong> </td></tr>
<tr><td align=right>200</td><td>fy</td><td><strong><code>+</code></strong>, <strong><code>-</code></strong>, <strong><code>\</code></strong> </td></tr>
<tr><td align=right>100</td><td>yfx</td><td><strong><code>.</code></strong> </td></tr>
<tr><td align=right>1</td><td>fx</td><td><strong><code>$</code></strong> </td></tr>
</table>
<div class="caption"><b>Table 5 : </b>System operators</div>
<a id="tab:operators"></a>
</dd>
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="current_op/3"><strong>current_op</strong>(<var>?Precedence,
?Type, ?:Name</var>)</a></dt>
<dd class="defbody">
True if <var>Name</var> is currently defined as an operator of type <var>Type</var>
with precedence <var>Precedence</var>. See also <a id="idx:op3:1198"></a><a class="pred" href="operators.html#op/3">op/3</a>.
</dd>
</dl>
<p></body></html>
|
