demonstrate datatype replication declarations of SML'97

demo.sml

(**
 * datatype replication declarations(specifications)のサンプル
 *)

(** monomorphic version *)
structure S =
struct
  datatype either = L | R
end

structure F1 =
struct
  type either = S.either
  val vL = S.L
end

structure F2 =
struct
  datatype either = datatype S.either (* datatype replication declarations *)
  val vL = S.L
end

(** polymorphic version *)
structure S =
struct
  datatype ('a,'b) poly_either = Left of 'a | Right of 'b
end

structure F1 =
struct
  type ('a,'b) poly_either = ('a,'b) S.poly_either
  val pvL = S.Left 5
end

structure F2 =
struct
  datatype poly_either = datatype S.poly_either (* datatype replication declarations *)
  val pvL = S.Left 5
end

http://d.hatena.ne.jp/eldesh/20130420/1366474660