[Haskell] Object-Orientation and Haskell

[Ralf Lammel]

>   Define a type A such that for any type B you can define
> 
>     up :: B -> A
>     down :: A -> Maybe B
> 
>   such that
> 
>     down . up = Just
> 
> You can do this quite easily in Java or C++, mutatis mutandis. You
can't
> do this in Haskell, I don't think. You can't actually do this in
> O'Haskell either, it seems the O' essentially amounts to syntactic
sugar.

You can't even do this in OCaml.
However, in OOHaskell you can.

>From the TOC of the OOHaskell paper
http://homepages.cwi.nl/~ralf/OOHaskell/

5.4 Casts based on dynamics		50
5.5 Casts based on unions		51

The second technique may add something to this discussion here.
We use a sort of intersection-type encoding (also reminiscent of TICs).

Thanks,
Ralf