### test.mli [ocaml]
type u
type 'a map

val add : u -> 'a -> 'a map -> 'a map

### test.ml [ocaml]
type u = int
module I = Map.Make(struct type t = u let compare = compare end)

type 'a map = 'a I.t

let add k v m =
  I.add k v m