Re: [Caml-list] Possibility of Nested Classes and Nested Inheritance?

[Jacques Garrigue <garrigue@math.nagoya-u.ac.jp>]

From: "Jørgen Hermanrud Fjeld" <jhf@hex.no>

> I just read about the work by Nystrom, Chong and Myers on nested
> inheritance, specifically the article "Scalable Extensibility via Nested
> Inheritance".
> 
> The article does demonstrate fascinating, to me, use of inheritance, and
> I wonder if it is possible to do something similar and
> object-oriented in OCaml.
> 
> To do something similar would, according to my understanding, require
> both inner classes and super-class polymorphism.
> In understand inner classes as implicitly polymorphic with respect
> to the enclosing class,
> and polymorphism on the super class as the practical ability to extend
> the type hierarchy upwards.
> 
> Do you know of any work that relate nested inheritance to OCaml, or that
> address the similar issuesof inner classes and super-class polymorphism?

Answer 1: there are no inner classes in ocaml.
Answer 2: there are plenty of other ways to obtain similar effects.

I don't know exactly what fascinated you in the paper, so it is hard
to answer precisely, but there are already a few techniques in ocaml to
solve the problems they describe.
(Of course they wouldn't cite them, as ocaml doesn't look like a
relevant language to them.)

Their compiler example seems to be a variant of the expression
problem.
There are several solutions to the expression problem in ocaml, using
either polymorphic variants
  http://wwwfun.kurims.kyoto-u.ac.jp/~garrigue/papers/fose2000.html
or objects
  http://pauillac.inria.fr/~remy/work/expr/

On the more general question of virtual types, Didier Rémy and Jérôme
Vouillon gave a detailed "refutation".
  http://pauillac.inria.fr/~remy/work/virtual/

So you can see if you can do all what you need with the above methods.
If you find some unexpected limitation, please let us now.

Jacques Garrigue