Use "with type" with functorial signatures

Dear OCaml users,

In a .mli file, I can write the following:


module type BAR = sig
   type t
end

module type FOO = functor (Bar:BAR) -> sig
   type u
   type t = Bar.t
end

module Make : FOO


but I would like to specialize the last line to express the following
idea:


module Make : FOO with type u = string


Is it possible without expanding the signature FOO?

Thanks in advance,
Chantal.