Changes to Typeable

Iavor Diatchki iavor.diatchki at
Tue Feb 14 17:18:55 CET 2012


On Mon, Feb 13, 2012 at 5:32 PM, Edward Kmett <ekmett at> wrote:
> There are fewer combinators from commonly used classes for working with
> the left argument of a bifunctor, however.

I think that the bifunctor part of Bas's version is a bit of a red herring.
 What I like about it is that it overloads exactly what needs to be
overloaded---the representation of the type---without the need for any fake
parameters.  To make things concrete, here is some code:

> newtype TypeRepT t = TR TypeRep
> class Typeable t where
>   typeRep :: TypeRepT t
> instacne Typeable Int where typeRep = TR type_rep_for_int
> instance Typeable []  where typeRep = TR type_rep_for_list

The two formulations support exactly the same interface (you can define
`Proxy` and the proxied `typeRep` in terms of this class) so I wouldn't say
that the one is easier to use that the other, but I think that this
formulation is slightly simpler because it avoids the dummy parameter to

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