Using .mli files and Map - dictionary

Question

I've read some similar questions and some online examples, but I still don't know how to write an .mli file in this particular case.
In my project, I use a general map module with int keys, which then I specialize depending on the values I want to store in. Let's say I want to use it to store pairs, so I have a file like this:
file dataStr.ml:
module IntOrder =
struct
type t = int
let compare = Pervasives.compare
end
module IntMap = Map.Make( IntOrder )
type couple = int * int
(* pretty names *)
type int2couple = couple IntMap.t
module Couples = struct type t = int2couple end
A file using this submodule would be:
file useMap.ml:
open DataStr
let use k m =
IntMap.add k ((Random.int 6), (Random.int 8)) m
with interface:
file useMap.mli:
open DataStr
val use : int -> Couples.t -> Couples.t
So far, so good.
Let's now suppose that I want to expose submodule Couples, but not type int2couple. I would then write this interface:
file dataStr.mli:
module IntMap : Map.S with type key = int
module Couples : sig type t end
(*
I'd like to avoid the redundancy of using
module Couples : sig type t = (int * int) IntMap.t end
*)
Problem is, if I do add this interface, I get this compile error:
Error: The implementation useMap.ml does not match the interface useMap.cmi:
Values do not match:
val use :
DataStr.IntMap.key ->
(int * int) DataStr.IntMap.t -> (int * int) DataStr.IntMap.t
is not included in
val use : int -> DataStr.Couples.t -> DataStr.Couples.t
Is there a way to write an interface that lets me do what I want to do, other than the "redundant" one in the comment?

Answer 1

As noted in the comments, there is no way to avoid redundancy between interface (mli file) and implementation (ml files) when instantiating a functor.
The best you can do is the following:
$ cat dataStr.mli:
module IntMap : Map.S with type key = int
type couple = int * int
type int2couple = couple IntMap.t
module Couples : sig type t = int2couple end
$ cat dataStr.ml:
module IntOrder =
struct
type t = int
let compare = Pervasives.compare
end
module IntMap = Map.Make( IntOrder )
type couple = int * int
type int2couple = couple IntMap.t
module Couples = struct type t = int2couple end