(*
 * Konzepte höherer Programmiersprachen (SS 2006)
 *
 * Übungsblatt 10 / Aufgabe 4
 *)

type stack = {push: int -> unit; pop: unit -> unit; top: unit -> int};;


(* Aufgabe 4a *)

let single_stack =
  let s = ref [] in
    {push = (fun x -> s := x :: !s);
     pop = (fun u -> s := List.tl !s);
     top = (fun u -> List.hd !s)};;

single_stack.push 1;;
single_stack.push 2;;
single_stack.pop ();;
single_stack.top ();;


(* Aufgabe 4b *)

let make_stack =
  fun u -> let s = ref [] in
    {push = (fun x -> s := x :: !s);
     pop = (fun u -> s := List.tl !s);
     top = (fun u -> List.hd !s)};;

let fst_stack = make_stack ();;
let snd_stack = make_stack ();;

fst_stack.push 7;;
snd_stack.push 8;;
fst_stack.top ();;