lib/mlton/basic/unique-id.fun

   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 functor UniqueId():> UNIQUE_ID =
   9    struct
  10       type t = unit ref
  11
  12       fun new(): t = ref()
  13
  14       val equals = Ref.equals
  15
  16       fun layout _ = Layout.empty
  17
  18       fun toString _ = ""
  19    end
  20
  21 functor UnitUniqueId():> UNIQUE_ID =
  22    struct
  23       open Unit
  24
  25       fun new() = ()
  26
  27       fun toString _ = ""
  28    end
  29
  30 functor IntUniqueId():> UNIQUE_ID =
  31    struct
  32       open Int
  33
  34       val cur: t ref = ref 0
  35
  36       fun new(): t = (Int.inc cur; !cur)
  37    end