lib/mlton/basic/result.sml

   1 (* Copyright (C) 1999-2006 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  *
   4  * MLton is released under a BSD-style license.
   5  * See the file MLton-LICENSE for details.
   6  *)
   7
   8 structure Result:> RESULT =
   9 struct
  10
  11 datatype 'a t =
  12    No of string
  13  | Yes of 'a
  14
  15 local
  16    open Layout
  17 in
  18    fun layout layoutA =
  19       fn No s => seq[str "No", paren(str s)]
  20        | Yes a => seq[str "Yes", paren(layoutA a)]
  21 end
  22
  23 fun map(r, f) =
  24    case r of
  25       No s => No s
  26     | Yes x => Yes(f x)
  27
  28 val isNo = fn No _ => true | _ => false
  29
  30 val isYes = fn Yes _ => true | _ => false
  31
  32 end