(* Carsten Schuermann *)
(* Observers in ML *)

let 
  fun apply f x k = k (f x)

  val observer = fn n => fn x => 
        (print ("Observer " ^ Int.toString n ^ ": observed " 
		^ Int.toString x ^ "\n") ; x) 

  val observers = observer 1 o observer 2
                  o observer 3 o observer 4

  val tester = fn x => apply (fn y => y + 1) x observers
in
  (apply (fn y => y + 1) 10 observers)
end