Hi all,
I've been playing with GHC's new generics features (see
http://www.haskell.org/ghc/docs/latest/html/users_guide/generic-programming.html). All the documentation I've seen suggests creating a "helper class" -- for instance, the GSerialize class in the above link -- on which one defines generic instances.
It seems to me that this isn't necessary. For example, here's the the example from the GHC docs, but without a helper class:
> -- set the phantom type of Rep to (), to avoid ambiguity
> from0 :: Generic a => a -> Rep a ()
> from0 = from
>
> data Bit = O | I
>
> class Serialize a where
> put :: a -> [Bit]
>
> default put :: (Generic a, Serialize (Rep a ())) => a -> [Bit]
> put = put . from0
>
> instance Serialize (U1 x) where
> put U1 = []
>
> instance (Serialize (a x), Serialize (b x)) => Serialize ((a :*: b) x) where
> put (x :*: y) = put x ++ put y
>
> instance (Serialize (a x), Serialize (b x)) => Serialize ((a :+: b) x) where
> put (L1 x) = O : put x
> put (R1 x) = I : put x
>
> instance (Serialize (a x)) => Serialize (M1 i c a x) where
> put (M1 x) = put x
>
> instance (Serialize a) => Serialize (K1 i a x) where
> put (K1 x) = put x
Regards,
Reiner