gadt_alist.ml

type _ t = I : int -> int t | F : float -> float t

module TEq = struct
  type 'a key = 'a t
  type 'a value = 'a t
  let equal : type a b . a key -> b key -> (a, b) Eq.t option =
    fun x y -> match x, y with
      | I a, I b -> if a = b then Some Eq.Refl else None
      | F a, F b ->  if a = b then Some Eq.Refl else None
      | _ -> None
end

module TAlist = Alist (TEq)