[Haskell-cafe] Reading open data types

[Isaac Dupree]

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Benja Fallenstein wrote:
> Hi all,
> 
> We've had a discussion on #haskell about how we can make a function
> that reads in serialized values of an open data type, such as
> 
> [...]
> However, this is still kind of boring. Is there a better way? If not,
> would it be a good idea to have compiler support for building this
> kind of type table?

Since Show instances can overlap (e.g. (show (1::Int)) == (show
(1::Integer))), we need to tag with the type.  Reminds me of Typeable.
Since GHC lets us derive Typeable with a guarantee of different types
being distinct (at least for a single compile-and-run session...), maybe
that can be leveraged somehow? (I see that was sort of mentioned in the
IRC discussion)

Isaac
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