Hi,
   
   My problem (example code):
   
   [omitted]

What about using abstraction? eg

    module type FOO1 =
    sig
      type 'a foo
      val empty : unit -> 'a foo
    end

    module Bar : FOO1 =
    struct
      type 'a foo = 'a list Lazy.t
      let empty () = lazy []
    end

Then empty is a function and its type gets generelized.

   The "'a" specified in "empty" is still not the same as in "'a foo". I have

The section about type checking in the list of "Frequently asked
Questions about Caml"
(http://caml.inria.fr/FAQ/FAQ_EXPERT-eng.html) explains the
differences between 'a and '_a.


Bye,

Hendrik