signature MLTON_MONO_VECTOR =
   sig
      type t
      type elem
      val fromPoly: elem vector -> t
      val toPoly: t -> elem vector
   end

• type t
  type of monomorphic vector

• type elem
  type of vector elements

• fromPoly v
  type cast a polymorphic vector to its monomorphic counterpart; in MLton, this is a constant-time operation

• toPoly v
  type cast a monomorphic vector to its polymorphic counterpart; in MLton, this is a constant-time operation