Instantiating L to a list of digits Prolog

Question

If I have the following database:

digit(0).
digit(1).
digit(2).
digit(3).
digit(4).
digit(5).
digit(6).
digit(7).
digit(8).
digit(9).

I want the query

digits([X,Y]). 

to succeed by instantiating X and Y to 10*10 = 100 different combinations of digits, how would I go about this?

Would I need to use finite domain constraints for this and something like

L ins 0..9

Thank you in advance

Answer 1

you don't need clpfd to do that. You can use higher order to obtain an expressive solution:

digits(L) :- maplist(digit, L).

You can also do the recursion yourself:

digits([]) :- [].
digits([H|T]) :- digit(H), digits(T).