prolog reflection (kind of)

[kahleen]

Hi!

I'm having the following problem. Suppose I have the knowledge base from below:

mom(13, bla, bli).
dad(15, foo).
grandma(18, a, b, c, d, e).
grandpa(19, x, y, z).

Each predicate has some parameters of which only the first is important to identify it. Identifiers are unique (or not, I don't think non-uniqueness will do any harm)

What's the best way to implement a predicate get_term that works like this?

?- get_term(13, X).
X = mom(13, bla, bli)

?- get_term(19, Y).
Y = grandpa(19, x, y, z)

Help will be greatly appreciated, thanks in advance

 

[joel76]

There is a way in SWI-Prolog :

:- dynamic (base/2).

mom(13, bla, bli).
dad(15, foo).
grandma(18, a, b, c, d, e).
grandpa(19, x, y, z).

my_index(Pred) :-
	Pred =.. [_, N | _],
	assert(base(N, Pred)).


init :-
	retractall(base(_,_)),
	my_index(mom(13, bla, bli)),
	my_index(dad(15, foo)),
	my_index(grandma(18, a, b, c, d, e)),
	my_index(grandpa(19, x, y, z)).


get_term(N, X) :-
	init,
	base(N, X).

for example

3 ?- get_term(13, X).
X = mom(13, bla, bli).

4 ?- get_term(19, X).
X = grandpa(19, x, y, z).

 

[kahleen]

Thank you very much ...

I'm not quite content yet with the part where I have to call my_index for each fact in the KB, given that the KB has many facts like mom and dad ... I don't know how to iterate through all the facts in the KB and call my_index on each of them ... but your solution is great otherwise

 

[joel76]

I modify my code and it is a little bit more usefull I think, you just have to know names and arity of facts :

:- dynamic (base/2).

mom(13, bla, bli).
dad(15, foo).
dad(16, foo_bis).
grandma(18, a, b, c, d, e).
grandpa(19, x, y, z).

my_index([Name, Arity]) :-
	functor(Pred, Name, Arity),
	forall( call(Pred),
		(   Pred =.. [_, N | _],
		    assert(base(N, Pred)))).


init :-
	retractall(base(_,_)),
	L = [[mom, 3], [dad, 2], [grandma, 6], [grandpa, 4]],
	maplist(my_index, L).


get_term(N, X) :-
	init,
	base(N, X).