72 lines
2.8 KiB
HTML
72 lines
2.8 KiB
HTML
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<?xml version="1.0" encoding="utf-8"?>
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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN"
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"http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
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<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en">
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<head>
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<meta http-equiv="content-type" content="application/xml+xhtml; charset=utf-8" />
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<title>Logtalk control construct: :/1</title>
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<link rel="stylesheet" href="../../screen.css" type="text/css" media="screen"/>
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<link rel="stylesheet" href="../../print.css" type="text/css" media="print"/>
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</head>
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<body>
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<div class="top-left">Logtalk reference manual</div>
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<div class="top-right">Control construct: :/1</div>
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<div class="bottom-left"><span class="page"/></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#constructs">control constructs</a></div>
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<h2 id="control_direct1" class="codenp">:/1</h2>
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<h4>Description</h4>
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<pre>:Goal</pre>
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<p>
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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.
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</p>
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<h4>Template and modes</h4>
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<pre>:+callable</pre>
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<h4>Errors</h4>
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<dl>
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<dt>Goal is a variable:</dt>
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<dd><code>instantiation_error</code></dd>
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<dt>Goal is neither a variable nor a callable term:</dt>
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<dd><code>type_error(callable, Goal)</code></dd>
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<dt>The object containing the call does not import any category:</dt>
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<dd><code>existence_error(procedure, Goal)</code></dd>
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</dl>
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<h4>Examples</h4>
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<pre>:- object(bounded_point,
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imports(bounded_coordinate),
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instantiates(class),
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specializes(point)).
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move(X, Y) :-
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:check_bounds(x, X), % defined in the "bounded_coordinate" category
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:check_bounds(y, Y),
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^^move(X, Y).</pre>
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<div class="footer">
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<div class="copyright">
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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: June 8, 2007</span>
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</div>
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<div class="navbottom">
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<span><a href="../index.html#constructs">previous</a> | <a href="../../glossary.html">glossary</a> | <a href="../index.html#constructs">next</a></span><br/>
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</body>
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