:- module(ac_list_util,
	[ list_offset/3,	% +List, +N, +SmallerList
          list_limit/4		% +List, +N, +FirstN, Rest
	]).


%%	list_offset(+List, +N, -SmallerList)
%
%	SmallerList starts at the nth element of List.

list_offset(L, N, []) :-
	length(L, Length),
	Length < N,
	!.
list_offset(L, N, L1) :-
	list_offset_(L, N, L1).

list_offset_(L, 0, L) :- !.
list_offset_([_|T], N, Rest) :-
	N1 is N-1,
	list_offset_(T, N1, Rest).

%%	list_limit(+List, +N, -SmallerList, -Rest)
%
%	SmallerList ends at the nth element of List.

list_limit(L, N, L, []) :-
	N < 0,
	!.
list_limit(L, N, L, []) :-
	length(L, Length),
	Length < N,
	!.
list_limit(L, N, L1, Rest) :-
	list_limit_(L, N, L1, Rest).

list_limit_(Rest, 0, [], Rest) :- !.
list_limit_([H|T], N, [H|T1], Rest) :-
	N1 is N-1,
	list_limit_(T, N1, T1, Rest).