With ocaml 3.06 we are now able to replace

    method with_foo : foo -> unit = ...
with
    method with_foo : 'a. (#foo as 'a) -> unit = ...

and get implicit subtyping when calling with_foo.


But I can't make it work when "foo" is a parametric variable:

    method with_foo : 'foo -> unit = ...
works whereas
    method with_foo : 'a. (#'foo as 'a) -> unit = ...
gives "Syntax error", and
    method with_foo : 'a. ('foo as 'a) -> unit = ...
gives "This type has no row variable"

Is there a solution?

thanks.


Full example: