Re: predicate_property help.

Amine Marref a écrit :
> Hi,
> 
> I use a meta-interpreter in my program. The meta-interpreter needs to 
> check whether a particular predicate is built-in or user-defined to 
> perform an iterative deepening DFS.
> .....
> solve(A,_,_):-
>  predicate_property(A, built_in),  !,
>  call(A).
> solve(A,D,Limit):-
>  predicate_property(A, user),
>  clause(A,B),
>  D1 is D+1,
>  solve(B,D1,Limit).
> ....
> 
> 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.
> so:
> 
> | ?- predicate_property(length/2, built_in).
> 
> yes
> | ?- 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/'
> 
> yes
> 
> However, 'length/2' does not work as first argument to predicate_property.
> 
> Any help?
> 
> Amine.
> 

Hi Amine,

Try this :

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

Arity = 2
Functor = length
Predicate_Indicator = length/2

yes

Predicate_Indicator is not an atom but must be a compound term 
'/'(Functor,Arity). That's why I use the "univ" predicate (=..) to build 
the term :

| ?- predicate_property('length/2', built_in).
uncaught exception: 
error(type_error(predicate_indicator,'length/2'),predicate_property/2)
| ?- predicate_property('/'(length,2), built_in).
yes
| ?- predicate_property(length/2, built_in).
yes

Good luck!

--
Ali ED-DBALI