:- object(object).
:- public(length/2).
length(List, Length) :-
integer(Length) ->
Length >= 0,
make_list(Length, List)
;
length(List, 0, Length).
make_list(0, []) :-
!.
make_list(N, [_| Tail]):-
M is N-1,
make_list(M, Tail).
length([], Length, Length).
length([_| Tail], Acc, Length) :-
Acc2 is Acc + 1,
length(Tail, Acc2, Length).
:- end_object.
