Practice of First-class module (generate new module)

gistfile1.ml

# module type Bumpable = sig
    type t
    val bump : t -> t
  end;;
module type Bumpable = sig type t val bump : t -> t end

# module Int_bumper = struct
    type t = int
    let bump n = n + 1
  end;;
module Int_bumper : sig type t = int val bump : t -> t end

# let int_bumper = (module Int_bumper : Bumpable with type t = int);;
val int_bumper : (module Bumpable with type t = int) = <module>

# let create_newbump (type a) (module B : Bumpable with type t = a) = 
(module struct
type t = B.t
let bump n = B.bump (B.bump n)
end : Bumpable with type t = a)
;;
val create_newbump : (module Bumpable with type t = 'a) -> (module Bumpable with type t = 'a) = <fun>

# let nb = create_newbump int_bumper;;
val nb : (module Bumpable with type t = int) = <module>

# module NB = (val nb : Bumpable with type t = int);;
module NB : sig type t = int val bump : t -> t end 

# NB.bump 3;;
- : int = 5