(* Carsten Schuermann *)
(* The visitor pattern in ML is just foldr *)

let 
  val E = [5, 2]

  val N = foldr (fn (x, y) => x*x :: y) nil E 
  val S = String.implode (foldr 
			  (fn (x, [c1, c2]) => c1 :: String.explode (Int.toString x) @ [c2]
			    | (x, c :: s) => c :: String.explode (Int.toString x)
			                     @ #"," :: #" " :: s)
			  [#"[", #"]"] 
			  E)
in
  (N, S)
end