/usr/lib/swi-prolog/doc/Manual/dynamic.html

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<h2 id="sec:declare"><a id="sec:4.14"><span class="sec-nr">4.14</span> <span class="sec-title">Declaring 
predicate properties</span></a></h2>

<a id="ch:dynamic"></a>
<a id="sec:declare"></a>

<p>This section describes directives which manipulate attributes of 
predicate definitions. The functors <a id="idx:dynamic1:743"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a>, <a id="idx:multifile1:744"></a><a class="pred" href="dynamic.html#multifile/1">multifile/1</a>,
<a id="idx:discontiguous1:745"></a><a class="pred" href="dynamic.html#discontiguous/1">discontiguous/1</a> 
and <a id="idx:public1:746"></a><a class="pred" href="dynamic.html#public/1">public/1</a> 
are operators of priority 1150 (see <a id="idx:op3:747"></a><a class="pred" href="operators.html#op/3">op/3</a>), 
which implies that the list of predicates they involve can just be a 
comma-separated list:

<pre class="code">
:- dynamic
        foo/0,
        baz/2.
</pre>

<p>In SWI-Prolog all these directives are just predicates. This implies 
they can also be called by a program. Do not rely on this feature if you 
want to maintain portability to other Prolog implementations.

<dl class="latex">
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="dynamic/1"><strong>dynamic</strong> <var>:PredicateIndicator, 
...</var></a></dt>
<dd class="defbody">
Informs the interpreter that the definition of the predicate(s) may 
change during execution (using <a id="idx:assert1:748"></a><a class="pred" href="db.html#assert/1">assert/1</a> 
and/or <a id="idx:retract1:749"></a><a class="pred" href="db.html#retract/1">retract/1</a>). 
In the multithreaded version, the clauses of dynamic predicates are 
shared between the threads. The directive <a id="idx:threadlocal1:750"></a><a class="pred" href="threadcom.html#thread_local/1">thread_local/1</a> 
provides an alternative where each thread has its own clause list for 
the predicate. Dynamic predicates can be turned into static ones using
<a id="idx:compilepredicates1:751"></a><a class="pred" href="dynamic.html#compile_predicates/1">compile_predicates/1</a>.</dd>
<dt class="pubdef"><a id="compile_predicates/1"><strong>compile_predicates</strong>(<var>:ListOfPredicateIndicators</var>)</a></dt>
<dd class="defbody">
Compile a list of specified dynamic predicates (see <a id="idx:dynamic1:752"></a><a class="pred" href="dynamic.html#dynamic/1">dynamic/1</a> 
and
<a id="idx:assert1:753"></a><a class="pred" href="db.html#assert/1">assert/1</a>) 
into normal static predicates. This call tells the Prolog environment 
the definition will not change anymore and further calls to <a id="idx:assert1:754"></a><a class="pred" href="db.html#assert/1">assert/1</a> 
or <a id="idx:retract1:755"></a><a class="pred" href="db.html#retract/1">retract/1</a> 
on the named predicates raise a permission error. This predicate is 
designed to deal with parts of the program that are generated at runtime 
but do not change during the remainder of the program execution.<sup class="fn">57<span class="fn-text">The 
specification of this predicate is from Richard O'Keefe. The 
implementation is allowed to optimise the predicate. This is not yet 
implemented. In multithreaded Prolog, however, static code runs faster 
as it does not require synchronisation. This is particularly true on SMP 
hardware.</span></sup></dd>
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="multifile/1"><strong>multifile</strong> <var>:PredicateIndicator, 
...</var></a></dt>
<dd class="defbody">
Informs the system that the specified predicate(s) may be defined over 
more than one file. This stops <a id="idx:consult1:756"></a><a class="pred" href="consulting.html#consult/1">consult/1</a> 
from redefining a predicate when a new definition is found.</dd>
<dt class="pubdef"><span class="pred-tag">[ISO]</span><a id="discontiguous/1"><strong>discontiguous</strong> <var>:PredicateIndicator, 
...</var></a></dt>
<dd class="defbody">
Informs the system that the clauses of the specified predicate(s) might 
not be together in the source file. See also <a id="idx:stylecheck1:757"></a><a class="pred" href="debugger.html#style_check/1">style_check/1</a>.</dd>
<dt class="pubdef"><a id="public/1"><strong>public</strong> <var>:PredicateIndicator, 
...</var></a></dt>
<dd class="defbody">
Instructs the cross-referencer that the predicate can be called. It has 
no semantics.<sup class="fn">58<span class="fn-text">This declaration is 
compatible with SICStus. In YAP, <a id="idx:public1:758"></a><a class="pred" href="dynamic.html#public/1">public/1</a> 
instructs the compiler to keep the source. As the source is always 
available in SWI-Prolog, our current interpretation also enhances the 
compatibility with YAP.</span></sup> The public declaration can be 
queried using <a id="idx:predicateproperty2:759"></a><a class="pred" href="examineprog.html#predicate_property/2">predicate_property/2</a>. 
The <a id="idx:public1:760"></a><a class="pred" href="dynamic.html#public/1">public/1</a> 
directive does
<em>not</em> export the predicate (see <a id="idx:module1:761"></a><a class="pred" href="mtoplevel.html#module/1">module/1</a> 
and <a id="idx:export1:762"></a><a class="pred" href="altmoduleapi.html#export/1">export/1</a>). 
The public directive is used for (1) direct calls into the module from, 
e.g., foreign code, (2) direct calls into the module from other modules, 
or (3) flag a predicate as being called if the call is generated by 
meta-calling constructs that are not analysed by the cross-referencer.
</dd>
</dl>

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swi-prolog-nox 6.6.4-2ubuntu1 / usr / lib / swi-prolog / doc / Manual / dynamic.html
