From: "Chris King" <colanderman@gmail.com>

> You can get the exact behavior you want using a pair of recursive
> modules (see the "Language Extensions" section of the manual), one for
> each of mypoint and mypointlist, but it's a lot more verbose (since
> recursive modules require you to explicity give their signatures).

I would think that one recursive module is sufficient.
Note also that, as this virtual class has no concrete methods, it
could just be defined as a class type (just means you can only use it
in interfaces and type annotations.) Then there is no code
duplication.

module rec Mypoint : sig
  class type p =
     object
       method getx : float
       method getlist : Mypoint.plist
     end
  type plist = Empty | Cons of (p * Mypoint.plist)
end = Mypoint

Jacques Garrigue