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Re: predicate_property help.

From: Paulo Moura
Subject: Re: predicate_property help.
Date: Tue, 2 Oct 2007 20:37:03 +0100

On 2007/10/02, at 15:20, Amine Marref wrote:

The above code works with Sicstus for instance. However, GNU Prolog needs A to be a predicate indicator e.g. length/2 and not a goal.



| ?- predicate_property(length/2, built_in).

| ?- predicate_property(length([a,b],2), built_in).
uncaught exception: error(type_error(predicate_indicator,length ([a,b],2)),predicate_property/2)

My question is then: how do I go from the goal length([a,b],2) to the predicate indicator length/2?

The best I could do was:

| ?- functor(length([a,b],2), Functor, Arity), atom_concat (Functor,/,Temp), number_atom(Arity, Arity1), atom_concat(Temp, Arity1, Predicate_Indicator).

Arity = 2
Arity1 = '2'
Functor = length
Predicate_Indicator = 'length/2'
Temp = 'length/'


However, 'length/2' does not work as first argument to predicate_property.

Of course not, 'length/2' is an atom. Try:

| ?- functor(length([a,b],2), Functor, Arity), predicate_property (Functor/Arity, built_in).

All the best,


Paulo Jorge Lopes de Moura
Dep. of Computer Science, University of Beira Interior
6201-001 Covilhã, Portugal

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