mlton/ssa/equatable.sig

   1 (* Copyright (C) 2004-2005 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 (*
   9  * Equatable values can be equated, after which they are equals.  Equating
  10  * two value requires the client to specify how to compute the new value from
  11  * the old.
  12  *
  13  * Equatable values can be either created by "new" or "delay".  In the case of
  14  * delay, the value is only computed if "value" is called.
  15  *
  16  * Equating a value created by delay with a value created by new will completely
  17  * drop the delayed value.  Hence, if a value is delayed, then nothing should
  18  * be assumed about any of its subcomponents.
  19  *)
  20
  21 signature EQUATABLE =
  22    sig
  23       type 'a t
  24
  25       val equals: 'a t * 'a t -> bool
  26       val delay: (unit -> 'a) -> 'a t
  27       val equate: 'a t * 'a t * ('a * 'a -> 'a) -> unit
  28       val layout: 'a t * ('a -> Layout.t) -> Layout.t
  29       val new: 'a -> 'a t
  30       val value: 'a t -> 'a
  31       val whenComputed: 'a t * ('a -> unit) -> unit
  32    end