module type BOX =
	sig
		type 'a option
		exception Err of string
		val create: unit -> 'a option                      (*tworzenie pudełka*)
		val put: 'a* 'a option -> 'a option                (*wkładanie do pudełka*)
		val pop: 'a option -> 'a option                    (*wyciąganie z pudełka*)
		(*val content: 'a option -> 'a*)
	end
;;

module Box : BOX =
	struct
		type 'a option = 'a list
		exception Err of string

		let create() = []
		let put = function
			| (s, []) -> [s];
			| (_, _) -> raise(Err("box is full"))

		let pop = function
			| [] -> raise (Err "Box is empty")
			| h -> []
(*
		let content = function
			| [] -> raise(Err "Box is empty")
			| h::_ -> h*)
	end
	;;