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<title>Logtalk control construct: :/1</title>
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<div class="top-left">Logtalk reference manual</div>
<div class="top-right">Control construct: :/1</div>
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<h2 id="control_direct1" class="codenp">:/1</h2>
<h4>Description</h4>
<pre>:Goal</pre>
<p>
Calls an imported category predicate without using the message sending mechanisms. The category predicate is called with the same execution context (<em>sender</em>, <em>this</em>, and <em>self</em>) as the predicate whose body contains the call. The lookup for both the predicate declaration and the predicate definition begins in <em>this</em>. For the predicate definition, the lookup is restricted to the imported categories. As a consequence, any redeclaration or redefinition of the predicate in a descendant of the object containing the call will be ignored.
</p>
<h4>Template and modes</h4>
<pre>:+callable</pre>
<h4>Errors</h4>
<dl>
<dt>Goal is a variable:</dt>
<dd><code>instantiation_error</code></dd>
<dt>Goal is neither a variable nor a callable term:</dt>
<dd><code>type_error(callable, Goal)</code></dd>
<dt>The object containing the call does not import any category:</dt>
<dd><code>existence_error(procedure, Goal)</code></dd>
</dl>
<h4>Examples</h4>
<pre>:- object(bounded_point,
imports(bounded_coordinate),
instantiates(class),
specializes(point)).
move(X, Y) :-
:check_bounds(x, X), % defined in the "bounded_coordinate" category
:check_bounds(y, Y),
^^move(X, Y).</pre>
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<span>Last updated on: June 8, 2007</span>
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