[Haskell-cafe] Re: Serialising types with existential data constructors

[Ashley Yakeley]

Misha Aizatulin wrote:
>   This is indeed the only solution I see so far. It has a serious
> problem though: as soon as I write the mapping, I limit once and for all
> the set of all types that can be used with my box. And I do so in a
> non-extensible way - if someone later would like to use my box with some
> other type in it, they wouldn't be able to.

This doesn't really help you now, but extending Haskell with open types 
and functions would solve this...
http://www.informatik.uni-bonn.de/~loeh/OpenDatatypes.pdf
http://haskell.org/haskellwiki/Extensible_datatypes

-- 
Ashley Yakeley