deriving show for sets?

module String = struct
  include String

  let show (t:string) = Printf.sprintf "%S" t
  let pp formatter t =
    Format.pp_print_string formatter t

end

module type E = sig
  type t
  val compare : t -> t -> int
  val show : t -> string
  val pp : Format.formatter -> t -> unit
end

module Set =
  struct

    module Make(E:E) = struct
      include Set.Make(E)
      let show (t:t) =
        let b = Buffer.create 128 in
        let n = cardinal t in
        Buffer.add_string b "{:";
        let c = ref 0 in
        iter
          (fun x ->
           Buffer.add_string b ([%show : E.t] x);
           incr c;
           if !c < n then Buffer.add_string b ", ";

          ) t;
        Buffer.add_string b ":}";
        Buffer.contents b

      let pp formatter t =
        Format.pp_print_string formatter (show t)
    end
end

module StringSet = Set.Make(String)

let test empty add show (xs:'a list) =
  let r = List.fold_left (fun acc x -> add x acc) empty xs in
  let my_val = [r] in
  Printf.printf "%s\n" (show my_val)

let ()= test
          StringSet.empty
          StringSet.add
          [%show: StringSet.t list]
          ["x";"y";"z"]

module Int32Set = Set.Make(
                      struct include Int32
                             let show = to_string
                             let pp formatter t =
                               Format.pp_print_string formatter (show t)
                      end)