(************************************************************
  opaque_manifest.sml

************************************************************)

structure X = 
  struct
    type t = int
    val x = (1:t)  (* val (x:t) = 1 でもよい *)
  end;;

signature XS = 
  sig
    type t;
    val x : t;
  end;;

structure XOpaque = X :> XS;;
structure XManifest = X : XS;;

val opaque_value = XOpaque.x;;
val manifest_value = XManifest.x;;

(** 実行結果
harp:~>sml
- use "opaque_manifest.sml";;
[opening opaque_manifest.sml]
structure X :
  sig
    type t = int
    val x : t
  end
signature XS =
  sig
    type t
    val x : t
  end
structure XOpaque : XS
structure XManifest : XS
val opaque_value = - : XOpaque.t
val manifest_value = 1 : X.t
val it = () : unit
- opaque_value;;
val it = - : XOpaque.t (* 抽象型 *)
- manifest_value;;
val it = 1 : X.t       (* Coreのintと互換性のある型 *)
**)