69 lines
2.7 KiB
HTML
69 lines
2.7 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: <</2</title>
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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: <</2</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_context2" class="codenp"><</2</h2>
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<h4>Description</h4>
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<pre>Object << Goal</pre>
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<p>
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Calls a goal within the context of the specified object. Goal is called with the execution context (<em>sender</em>, <em>this</em>, and <em>self</em>) set to Object. Goal may need to be written within brackets to avoid parsing errors due to operator clashes. This control construct is mainly used for debugging and for writing object unit tests.
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</p>
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<h4>Template and modes</h4>
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<pre>+object_identifier << +callable</pre>
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<h4>Errors</h4>
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<dl>
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<dt>Either Object or Goal is a variable:</dt>
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<dd><code>instantiation_error</code></dd>
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<dt>Object is neither a variable nor a valid object identifier:</dt>
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<dd><code>type_error(object_identifier, Goal)</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>Object does not contain a local definition for the Goal predicate:</dt>
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<dd><code>existence_error(procedure, Goal)</code></dd>
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<dt>Object does not exist:</dt>
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<dd><code>existence_error(object, Object)</code></dd>
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</dl>
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<h4>Examples</h4>
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<pre>test(member) :-
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list << member(1, [1]).</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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