explicit dicts

module type TC =
sig
  type t
  val x : t -> t -> t
  val y : t -> unit
end

module X1 =
struct
  type t = int
  let x = (+)
  let y = Printf.printf "%d\n"
end

(* this is 3.12.1, you can drop most most type annotations in 4.00 *)
let f (type a) (tc : (module TC with type t = a)) (x : a) : a=
  let module M = (val tc : TC with type t = a) in
    M.x x x

#use "tc.ml";;
module type TC = sig type t val x : t -> t -> t val y : t -> unit end
module X1 :
  sig type t = int val x : int -> int -> int val y : int -> unit end
val f : (module TC with type t = 'a) -> 'a -> 'a = <fun>