[Caml-list] implicit subtyping fails with recursive classes

[Goswin von Brederlow <goswin-v-b@web.de>]

Hi,

I'm trying to add implicit subtyping to a pair of recurisve classes:

Without subtyping:
------------------
class type foo = object method foo : t -> unit end
and t = object method push : foo -> unit end

With that I can call t#push (x :> foo) for any x that implements the
foo interface.


What I want:
------------
# class type foo = object method foo : t -> unit end
and t = object method push : 'a . (#foo as 'a) -> unit end;;
                             ^^^^^^^^^^^^^^^^^^^^^^^^^
Error: The universal type variable 'a cannot be generalized:
       it escapes its scope.



The problem seems to be the recursive definition with "and". Here is
an example with and without "and":

(* works *)
class type foo = object method foo : string end;;
class type bar = object inherit foo method bar : string end;;
class type t = object method push : 'a . (#foo as 'a) -> unit end;;

(* fails *)
class type foo = object method foo : string end
and bar = object inherit foo method bar : string end
and t = object method push : 'a . (#foo as 'a) -> unit end;;


So what am I doing wrong?

MfG
	Goswin