signature MLTON_MONO_ARRAY =
   sig
      type t
      type elem
      val fromPoly: elem array -> t
      val toPoly: t -> elem array
   end

• type t
  type of monomorphic array

• type elem
  type of array elements

• fromPoly a
  type cast a polymorphic array to its monomorphic counterpart; the argument and result arrays share the same identity

• toPoly a
  type cast a monomorphic array to its polymorphic counterpart; the argument and result arrays share the same identity