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< title > Logtalk built-in method: parameter/2< / title >
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< div class = "top-left" > Logtalk reference manual< / div >
< div class = "top-right" > Built-in method: parameter/2< / 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#methods" > built-in methods< / a > < / div >
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< h2 class = "code" > parameter/2< / h2 >
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< h4 > Description< / h4 >
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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 unification between its second argument and the corresponding implicit context argument in the predicate containing the call. This unification 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 >
< h4 > Template and modes< / h4 >
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< pre > parameter(+integer, ?term)< / pre >
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< h4 > Errors< / h4 >
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< dl class = "errors" >
< dt > Number is a variable:< / dt >
< dd > < code > instantiation_error< / code > < / dd >
< dt > Number is neither a variable nor an integer value:< / dt >
< dd > < code > type_error(integer, Number)< / code > < / dd >
< dt > Object identifier is not a compound term:< / dt >
< dd > < code > type_error(compound, Object)< / code > < / dd >
< dt > Number is a negative integer value:< / dt >
< dd > < code > domain_error(not_less_than_zero, Number)< / code > < / dd >
< / dl >
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< h4 > Examples< / h4 >
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< pre > :- object(box(_color, _weight)).
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...
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color(Color) :- % this clause is translated to a fact upon compilation
parameter(1, Color).
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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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< div class = "copyright" > Copyright © < a href = "mailto:pmoura@logtalk.org" > Paulo Moura< / a > — < a href = "http://www.logtalk.org" > Logtalk.org< / a > < / div >
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< span class = "date" > Last updated on: February 11, 2006< / span >
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