Counting Sublist Elements in Prolog

prolog

Solution

len([H|T],N) :-
    len(H, LH),
    len(T, LT),
    !,
    N is LH + LT.
len([], 0):-!.
len(_, 1):-!.

Test:

?- len([a,b,[c,d,e],f],Output).
Output = 6.

Problem

How can I count nested list elements in Prolog? I have the following predicates defined, which will count a nested list as one element: ``` length([ ], 0). length([H|T],N) :- length(T,M), N is M+1. ``` Usage: ``` ?- length([a,b,c],Out). Out = 3 ``` This works, but I would like to count nested elements as well i.e. ``` length([a,b,[c,d,e],f],Output). ?- length([a,b,[c,d,e],f],Output). ``` Output = 6

Original source