(* Copyright (C) 1999-2006 Henry Cejtin, Matthew Fluet, Suresh
 *    Jagannathan, and Stephen Weeks.
 *
 * MLton is released under a BSD-style license.
 * See the file MLton-LICENSE for details.
 *)

structure Option: OPTION =
struct

type 'a t = 'a option

open Pervasive.Option

fun fold (opt, b, f) =
   case opt of
      NONE => b
    | SOME x => f (x, b)

fun exists (z, f) =
   case z of
      NONE => false
    | SOME x => f x

fun forall (z, f) =
   case z of
      NONE => true
    | SOME x => f x

fun foreach (opt, f) =
   case opt of
      NONE => ()
    | SOME x => f x

val app = foreach

fun map (opt, f) =
   case opt of
      NONE => NONE
    | SOME x => SOME (f x)

fun equals (o1, o2, eq) =
   case (o1, o2) of
      (NONE, NONE) => true
    | (SOME x, SOME y) => eq (x, y)
    | _ => false

fun isNone opt =
   case opt of
      NONE => true
    | SOME _ => false

fun toString xToString opt =
   case opt of
      NONE => "None"
    | SOME x => concat ["Some ", xToString x]

fun layout layoutX opt =
   let
      open Layout
   in
      case opt of
         NONE => str "None"
       | SOME x => seq [str "Some ", layoutX x]
   end

end