80c28e1507
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84 lines
2.8 KiB
HTML
84 lines
2.8 KiB
HTML
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<title>Logtalk built-in method: parameter/2</title>
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</head>
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<body>
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<div class="navtop">
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<a href="../../index.html">contents</a> > <a href="../index.html">reference manual</a> > <a href="../index.html#methods">built-in methods</a>
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</div>
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<h2><code>parameter/2</code></h2>
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<h4>Description</h4>
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<blockquote>
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<pre>parameter(Number, Term)</pre>
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<p>
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Normally used only in <a class="glossary" title="Go to glossary definition" href="../../glossary.html#parametric">parametric objects</a>, this method returns parameter values by using the parameter position in the object identifier. Note that this predicate implies an instantiation between its second argument and the corresponding implicit context argument in the predicate containing the call. This instantiation occurs at the clause head, not at the clause body. See also <a href="this1.html"><code>this/1</code></a>.
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</p>
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</blockquote>
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<h4>Template and modes</h4>
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<blockquote>
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<pre>parameter(+integer, ?term)</pre>
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</blockquote>
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<h4>Errors</h4>
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<blockquote>
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<dl>
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<dt>Number is a variable:</dt>
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<dd><code>instantiation_error</code></dd>
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<dt>Number is neither a variable nor an integer value:</dt>
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<dd><code>type_error(integer, Number)</code></dd>
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<dt>Object identifier is not a compound term:</dt>
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<dd><code>type_error(compound, Object)</code></dd>
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<dt>Number is a negative integer value:</dt>
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<dd><code>domain_error(not_less_than_zero, Number)</code></dd>
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</dl>
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</blockquote>
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<h4>Examples</h4>
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<blockquote>
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<pre>:- object(box(_colour, _weight)).
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...
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colour(Colour) :- % this clause is translated to a fact upon compilation
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parameter(1, Colour).
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heavy :-
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parameter(2, Weight), % after compilation, the >/2 call will be the first
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Weight > 10. % condition on the clause body
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...</pre>
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</blockquote>
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<div class="navbottom">
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<a href="../index.html#methods">previous</a> | <a href="../../glossary.html">glossary</a> | <a href="self1.html">next</a>
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<div class="copyright">
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Copyright © <a href="mailto:pmoura@logtalk.org">Paulo Moura</a> — <a href="http://www.logtalk.org">Logtalk.org</a>
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