(* Copyright (C) 1999-2005 Henry Cejtin, Matthew Fluet, Suresh
 *    Jagannathan, and Stephen Weeks.
 *
 * MLton is released under a BSD-style license.
 * See the file MLton-LICENSE for details.
 *)

functor Sum(S: SUM_STRUCTS): SUM =
struct

open S

datatype t =
   X of X.t
 | Y of Y.t

val outX =
   fn X x => x
    | _ => Error.bug "Sum.outX"

val outY =
   fn Y y => y
    | _ => Error.bug "Sum.outY"

val map =
   fn (X x, f, _) => f x
    | (Y y, _, f) => f y

val equals =
   fn (X l, X l') => X.equals(l, l')
    | (Y l, Y l') => Y.equals(l, l')
    | _ => false

fun layout s = map(s, X.layout, Y.layout)

end