signature BLAH =
sig

  type t (* abstract data type *)
  val getX : t -> int
  val getBunny : t -> bunny

end

structure Blah :> BLAH =
(* the implementation may choose it's own way of implementing getX and getBunny *)
struct

  open Susp (* lazy evaluation library *)

  type t = {x : int, b : bunny susp} (* for implementor's convenience or just on a whim we take t to be a record. Bunny is computed lazily (don't ask) *)

  val getX = x (* I'm not sure if this compiles in SML, but it should *)
  val getBunny = force bunny (* same provision as above *)

end