[Caml-list] typechecking in 4.05+beta2

[Virgile Prevosto <virgile.prevosto@m4x.org>]

Dear list,

while playing with the new beta, I stumbled upon the following issue.
The program below is now rejected by the compiler, while this was not
the case with 4.04.

--- test.mli:
module M(E: sig type t end): sig
type t
val u: t -> t -> t
end

--- test.ml:
module M(E: sig type t end) = struct
type t = (E.t, unit) Hashtbl.t
let u = Hashtbl.fold (fun x () h -> Hashtbl.add h x (); h)
end

---
ocamlc test.mli
ocamlc test.ml
File "test.ml", line 1:
Error: The implementation test.ml does not match the interface test.cmi:
       ...
       At position module M(E) : <here>
       Modules do not match:
         sig
           type t = (E.t, unit) Hashtbl.t
           val u :
             ('_a, unit) Hashtbl.t ->
             ('_a, unit) Hashtbl.t -> ('_a, unit) Hashtbl.t
         end
       is not included in
         sig type t val u : t -> t -> t end
       At position module M(E) : <here>
       Values do not match:
         val u :
           ('_a, unit) Hashtbl.t ->
           ('_a, unit) Hashtbl.t -> ('_a, unit) Hashtbl.t
       is not included in
         val u : t -> t -> t
       File "test.ml", line 3, characters 4-5: Actual declaration

It is quite easy to fix, but I was wondering whether this restriction
in type unification when checking the conformance of .ml and .mli was
intended, and if yes, what is the reason behind it?
Note that this is of course a reduction of the initial code, and all
ingredients seems to be needed.

Best regards,
-- 
E tutto per oggi, a la prossima volta
Virgile