Simple Prolog Program - Please help!!

[Guest_imported]

How do i write a program that computes the sum of nested lists of numbers?

The list can contain either just numbers, of lists of numbers.
An example of how the program should work is:
?-sum([1,2,[3,4],5],S) would return S=15.

Right now I can add just numbers, but not lists of numbers:
sum([],0).
sum([H|T],N) :-
sum(T,N1),
N is H + N1.

 

[pimi]

How about this program?

sum([], 0) :- !.

sum(N, N) :- number(N), !.

sum([H|T], N) :-
sum(H, N1),
sum(T, N2),
N is N1 + N2.