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62 lines
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62 lines
2.6 KiB
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<title>Logtalk predicate directive: meta_predicate/1</title>
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<div class="top-left">Logtalk reference manual</div>
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<div class="top-right">Predicate directive: meta_predicate/1</div>
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<div class="bottom-right"><span class="page"/></div>
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<div class="navtop"><a href="../../index.html">contents</a> > <a href="../index.html">reference manual</a> > <a href="../index.html#directives">directives</a></div>
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<h2 class="codenp">meta_predicate/1<span id="directives_meta_predicate1"/></h2>
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<h4>Description</h4>
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<pre>meta_predicate(MetaPredicate)</pre>
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<p>
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Declares meta-predicates, i.e., predicates that have arguments that will be called as goals. An argument may also be a <em>closure</em> instead of a goal if the meta-predicate uses the <a title="Consult reference manual" href="../methods/call1.html"><code>call/N</code></a> Logtalk built-in methods to construct the actual goal from the closure and the additional arguments.
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</p>
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<p>
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Meta-arguments which are goals are represented by the atom <code>::</code> (for consistency with the message sending operators). Meta-arguments which are closures are represented by a positive integer, <code>N</code>, representing the number of additional arguments that will be appended to the closure in order to construct the corresponding meta-call. Normal arguments are represented by the atom <code>*</code>.
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</p>
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<h4>Template and modes</h4>
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<pre>meta_predicate(+meta_predicate_mode_indicator)</pre>
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<h4>Examples</h4>
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<pre>:- meta_predicate(findall(*, ::, *)).
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:- meta_predicate(forall(::, ::)).
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:- meta_predicate(maplist(2, *, *))</pre>
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<span>Copyright © <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> — <a href="http://logtalk.org">Logtalk.org</a></span><br/>
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<span>Last updated on: March 5, 2007</span>
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