predicate_property help.

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.

-- 
Amine Marref
PhD Research Student
Real-Time Systems Group
Department of Computer Science
The University of York
Heslington
YO10 5DD
York
United Kingdom

+44 1904 432810