(* generic tags *)
module type Tag = sig type 'a tag end

module Tagging (T : Tag) = struct
  module type Tagged = sig
    val tag : 'a -> bool -> 'a T.tag
    val get_tag : 'a T.tag -> bool
    val get_a : 'a T.tag -> 'a
    val process : 'a T.tag -> ('a -> 'b) -> ('a -> 'b) -> 'b
  end
end 

(****  implementations of Tag *****)
module BoolTag = struct
  type 'a tag = 'a * bool
end

module OptTag = struct
  type 'a tag = 'a option
end

(* open StateCPSMonad presently unused *)

module TaggingA (TAG : Tag)(T : Abstract.T) = struct
  module type Tagged = sig
    type 'a tag = 'a TAG.tag
    val tag : 'a T.abstract -> bool T.abstract -> 'a tag T.abstract
    val get_tag : 'a tag T.abstract -> bool T.abstract
    val process : 'a tag T.abstract -> 
      ((bool T.abstract -> ('b -> ('x -> 'y -> 'y) -> unit T.abstract)) option) ->
      ('a T.abstract -> ('b -> ('c -> 'd -> 'd) -> 'e T.abstract)) ->
      (unit          -> ('b -> ('f -> 'g -> 'g) -> 'e T.abstract)) ->
                        ('b -> ('b -> 'e T.abstract -> 'h) -> 'h)
  end
end