[Caml-list] Labels at the module level?

[Kenichi Asai <asai@is.ocha.ac.jp>]

Using labeled arguments, one can supply default values for unspecified
arguments:

let f ?(x = 3) y = x * y
in f 5

will return 15 without specifying the value of x at the second line.
Is there a way to do a similar thing at the module level?  Namely, I
want to define a functor that accepts a module of sig:

module type A_t = sig
  val x : int
  val y : int
end

but if the user did not specify some of the values in the signature,
some default values will be used.

Background: in the universe library for OCaml:

http://pllab.is.ocha.ac.jp/~asai/Universe/

one specifies various handlers for events (such as tick, mouse, and
key events).  Currently, these handlers are registered to the big_bang
function that accepts them using labeled arguments (with default
values).  I wonder if I can specify the interface as a module
signature and let the user write a module of that signature but only
those handlers that the user is interested in.

-- 
Kenichi Asai