lib/mlton/basic/pointer.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 Pointer: POINTER =
   9 struct
  10
  11 datatype 'a t = T of 'a option ref
  12
  13 fun !(T r) =
  14    case Ref.! r of
  15       NONE => Error.bug "Pointer.!"
  16     | SOME v => v
  17
  18 fun (T r) := v = Ref.:=(r, SOME v)
  19
  20 fun clear(T r) = Ref.:=(r, NONE)
  21
  22 fun copy(T r, T r') = Ref.:=(r, Ref.! r')
  23
  24 fun eq(T r, T r') = Ref.equals(r, r')
  25
  26 fun follow(T r) = Ref.! r
  27
  28 fun equals(p, p', equals) =
  29    case (follow p, follow p') of
  30       (NONE, NONE) => true
  31     | (SOME v, SOME v') => equals(v, v')
  32     | _ => false
  33
  34 fun isNull p = Option.isNone(follow p)
  35
  36 fun make v = T(ref v)
  37
  38 fun new v = make(SOME v)
  39
  40 fun null() = make NONE
  41
  42 fun swap(T p, T p') = Ref.swap(p, p')
  43
  44 end