datatype list 'a+
datacon nil : -all 'a- list 'a
datacon ::  : -all 'a- 'a * list 'a -> list 'a

type dyn = int / real / string    (* ICFP paper used \/ for union *)

val toString : dyn -> string
fun toString x =
  (Int.toString ,,
   (fn s => s : string) ,,
   Real.toString)  x

val hetListToString : list dyn -> string
fun hetListToString xs = case xs of
    nil   => "nil"
  | h::t => (toString h) ^ "::"
          ^ (hetListToString t)

val _ = print "\n\n"
val _ = print (hetListToString
                [1, 2, "what", 3.14159, 4, "why"])
val _ = print "\n\n\n"