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Date: Sun, 14 Jul 2002 21:08:12 -0500
From: Brian Smith <brian-l-smith@uiowa.edu>
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CC: caml-list@inria.fr
Subject: Re: [Caml-list] polymorphic methods
References: <3D320665.AC5539CD@noos.fr> <20020715100504O.garrigue@kurims.kyoto-u.ac.jp>
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Jacques Garrigue wrote:
> 
> Sorry, but there is no handling of instanciation via subtyping.
> Currently subtyping and instanciation are orthogonal concepts: you
> cannot subtype in an .mli, and you cannot instanciate an
> explicitly polymorphic type when subtyping.
> I believe it's correct, but you won't make me write the code without a
> proof :-)

That is really an interesting comment. I wonder, what are people 
currently researching w.r.t. the object-oriented features of O'Caml? 
Besides the above, Jacques said that recursive types with classes is not 
completely defined because (paraphrasing) recursive types are 
polymorphic and recursive classes are monomorphic:

     type variant = Node of node
     and
     class node =
       object
         method as_variant : variant = Node self
       end

I wonder, does a similar problem apply to recursive exceptions and classes?:

     (* email me for a complete example *)
     exception NotFound of node
     and
     class node  =
       object
         method find x = ... else raise (NotFound self)
       end;;

And, similarly, it does seem odd that currently it is impossible to 
create a polymorphic method equivalent to "map" (This type of problem is 
mentioned in http://citeseer.nj.nec.com/remy98objective.html).

Besides polymorphism, I wonder if it is possible to add open classes and 
multiple dispatch to O'Caml like MultiJava does for Java 
(http://www.cs.iastate.edu/~cclifton/multijava/).

I'm just a beginner and I don't know any of the theory of this yet, so 
i'm hoping somebody else will give Jacques some proofs of solutions to 
the above :)

Thanks,
Brian



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