[Haskell-cafe] Reducing boilerplate

[Sylvain Henry]

Hi,

To write FFI bindings, I use c-storable-deriving [1] to automatically
derive CStorable instances for many data types (the only difference
between Storable and CStorable is that CStorable provides default
methods for types that have Generic instances):

{-# LANGUAGE DeriveGeneric #-}
{-# LANGUAGE DeriveAnyClass #-}
...
data X = X
   { fieldStatus           :: Vector 24 Word8
   , fieldPadding         :: Word8
   } deriving (Generic, CStorable)

However I also need a Storable instance, hence I have to write (the
"c*" methods are provided by CStorable):

instance Storable X where
   peek        = cPeek
   poke        = cPoke
   alignment = cAlignment
   sizeOf      = cSizeOf

Is there a way to automatically generate this instance for every data
that has an instance of CStorable? Ideally, I would like to say once
and for all:

instance CStorable a => Storable a where
   peek        = cPeek
   poke        = cPoke
   alignment = cAlignment
   sizeOf      = cSizeOf

As I don't think it is currently possible, would it be sensible to add
the support for automatically derived instances attached to classes
(as a GHC extension)?

Regards,
Sylvain

[1] https://hackage.haskell.org/package/c-storable-deriving