To count the number of elements in a list in PROLOG.

list([],0).
list([H|T],C):-list(T,Y),C is Y+1.


Output

1 ?- list([1,2,3,5],C).
C = 4.

2 ?- list([1,2,3,5,4,5,6,7],C).
C = 8.

3 ?- list([],C).
C = 0.