basis-library/general/option.sml

   1 (* Copyright (C) 1999-2005 Henry Cejtin, Matthew Fluet, Suresh
   2  *    Jagannathan, and Stephen Weeks.
   3  * Copyright (C) 1997-2000 NEC Research Institute.
   4  *
   5  * MLton is released under a BSD-style license.
   6  * See the file MLton-LICENSE for details.
   7  *)
   8
   9 structure Option: OPTION =
  10 struct
  11
  12 datatype option = datatype option
  13
  14 exception Option
  15
  16 fun map f =
  17    fn NONE => NONE
  18     | SOME a => SOME (f a)
  19
  20 fun app f z = (ignore (map f z); ())
  21
  22 fun compose (f, g) c = map f (g c)
  23
  24 val join =
  25    fn NONE => NONE
  26     | SOME v => v
  27
  28 fun mapPartial f = join o (map f)
  29
  30 fun composePartial (f, g) = (mapPartial f) o g
  31
  32 fun filter f a = if f a then SOME a else NONE
  33
  34 fun getOpt (z, a) =
  35    case z of
  36       NONE => a
  37     | SOME v => v
  38
  39 val isSome =
  40    fn NONE => false
  41     | SOME _ => true
  42
  43 val valOf =
  44    fn NONE => raise Option
  45     | SOME v => v
  46
  47 end
  48
  49 structure OptionGlobal: OPTION_GLOBAL = Option
  50 open OptionGlobal