Am Di., 8. Okt. 2019 um 16:57 Uhr schrieb Simon Jakobi via Libraries < libraries@haskell.org>:

That seems like a good idea! [...]

Looks OK, but let's use toEnum in peekElemOff: instance Storable Ordering where sizeOf _ = sizeOf (undefined :: CInt) alignment _ = alignment (undefined :: CInt) peekElemOff p i = toEnum . fromIntegral <$> peekElemOff (castPtr p :: Ptr CInt) i pokeElemOff p i = pokeElemOff (castPtr p :: Ptr CInt) i . fromIntegral . fromEnum This is more symmetrical with pokeElemOff and less obfuscated. Note that the instance works for every Enum, so if there are more cases like Ordering, it might be worth to abstract that out.

But shouldn't Ordering have the alignment and size of Int8 rather than that of Int? At least in principle? On Tue, Oct 8, 2019, 11:38 AM David Feuer wrote:

newtype WrappedEnum a = WrappedEnum a

instance Enum a => Storable (WrappedEnum a) where ...

deriving via (WrappedEnum Ordering) instance Storable Ordering

On Tue, Oct 8, 2019, 11:34 AM Sven Panne wrote:

...

Am Di., 8. Okt. 2019 um 16:57 Uhr schrieb Simon Jakobi via Libraries < libraries@haskell.org>:

...

That seems like a good idea! [...]

Looks OK, but let's use toEnum in peekElemOff:

instance Storable Ordering where sizeOf _ = sizeOf (undefined :: CInt) alignment _ = alignment (undefined :: CInt) peekElemOff p i = toEnum . fromIntegral <$> peekElemOff (castPtr p :: Ptr CInt) i pokeElemOff p i = pokeElemOff (castPtr p :: Ptr CInt) i . fromIntegral . fromEnum

This is more symmetrical with pokeElemOff and less obfuscated. Note that the instance works for every Enum, so if there are more cases like Ordering, it might be worth to abstract that out. _______________________________________________ Libraries mailing list Libraries@haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/libraries

Yes, yours is better, but I'd go with Enum on both ends rather than relying on rewrite rules to make sure fromIntegral isn't slow. On Tue, Oct 8, 2019, 11:49 AM Henning Thielemann < lemming@henning-thielemann.de> wrote:

On Tue, 8 Oct 2019, David Feuer wrote:

...

newtype WrappedEnum a = WrappedEnum a instance Enum a => Storable (WrappedEnum a) where ...

That's almost what I recently defined in a custom package:

https://hub.darcs.net/thielema/storable-enum/browse/src/Data/Enum/Storable.h...

But I also let the user choose the underlying machine type.