Ocaml extending Map

test.ml

module type S = sig
  type key
  type atom
  type t
  
  val f: t -> t -> t
  val a: atom -> t -> t * t
end

(* I would like Make to have a partial signature of S *)
module Make (Key: OrderedType) (Atom: Atomic) (* : S *) = struct
  module Base = Map.Make(Key)

  type key = Key.t
  type atom = Atom.t
  type t = atom Base.t

  include Base

  (* Extending map basing on Map 'a t = Atom.t t *)
  let f = ...
  let a = ...
end