[Haskell-cafe] Implementation of "Dynamic" datatype

[Isaac Dupree]

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Stefan O'Rear wrote:
> the current type:
> 
> data Dynamic = Dynamic TypeRep Obj
> 
> the new type, if lucky:

Meaning the one with "Typeable a =>" instead of TypeRep?

> 
> data Dynamic = Dynamic !(a -> TypeRep) a
> 
> if unlucky:
> 
> data TypeableD a = TypeableD (a -> TypeRep)
> data Dynamic = Dynamic (TypeableD a) a
> 
> either way, the typeclass approach gives a lot more boxing.
> 

Yes, that's why I don't really propose that, because it's probably
inefficient (for dictionary-passing-based implementations anyway), just
that the "Obj" in Dynamic's constructor should be, type-system-wise, an
existential instead (which I don't think will change the runtime
representation, but I don't know how to test that).

Isaac
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