On Fri, Sep 21, 2012 at 10:21 AM, Herbert Valerio Riedel <hvr@gnu.org> wrote:

Hello Simon (et al.),

Some time ago, the `generic-deepseq` package was announced to the
haskell-cafe list, and some discussion took place[1], and the suggestion
came up that it might useful to be included to `deepseq` somehow.

IMHO, a least introduing way (which I've been using myself) would be to
add something along the code below to the `Control.DeepSeq` module (only
`genericsRnf` shall be exported, thus avoiding a PVP-major-bump):

-- | Generics-based 'rnf' implementation
genericsRnf :: (Generic a, GNFData (Rep a)) => a -> ()
genericsRnf = grnf_ . from
{-# INLINE genericRnf #-}

-- | Hidden type-class, /not/ exported
class GNFData f where
grnf_ :: f a -> ()

instance GNFData U1 where
grnf_ !U1 = ()
{-# INLINE grnf_ #-}

instance NFData a => GNFData (K1 i a) where
grnf_ = rnf . unK1
{-# INLINE grnf_ #-}

instance GNFData a => GNFData (M1 i c a) where
grnf_ = grnf_ . unM1
{-# INLINE grnf_ #-}

instance (GNFData a, GNFData b) => GNFData (a :*: b) where
grnf_ (x :*: y) = grnf_ x `seq` grnf_ y
{-# INLINE grnf_ #-}

instance (GNFData a, GNFData b) => GNFData (a :+: b) where
grnf_ (L1 x) = grnf_ x
grnf_ (R1 x) = grnf_ x
{-# INLINE grnf_ #-}

this way, the client code can then chose to use a Generics-derived `rnf`
implementation expliclity by simply declaring:

instance NFData FooBar where rnf = genericsRnf

...does this sound sensible?

cheers,
hvr

[1]: http://www.haskell.org/pipermail/haskell-cafe/2012-February/099551.html

--

_______________________________________________
Libraries mailing list
Libraries@haskell.org
http://www.haskell.org/mailman/listinfo/libraries