let len_list x =
	let rec helper a x =
		match x with
		| [] -> a
		| h::t -> helper (a + 1) t in
	helper 0 x;;

let sum_list x =
	let rec helper a x =
		match x with
		| [] -> a
		| h::t -> helper (a + h) t in
	helper 0 x;;

let max_list x =
	let rec helper a x =
		match x with
		| [] -> a
		| h::t -> helper (max a h) t in
	helper 0 x;;

let len_list_fold x = List.fold_left (fun a _ -> a + 1) 0 x
let sum_list_fold x = List.fold_left (fun a v -> a + v) 0 x
let max_list_fold x = List.fold_left (fun a v -> max a v) 0 x