I don't know exact sementics of Storable, but it's addable anyway. instance Storable http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... Ordering where sizeOf http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... _ = sizeOf http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... (undefined http://hackage.haskell.org/package/base-4.12.0.0/docs/src/GHC.Err.html#undef...::HTYPE_INT) alignment http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... _ = alignment http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... (undefined http://hackage.haskell.org/package/base-4.12.0.0/docs/src/GHC.Err.html#undef...::HTYPE_INT) peekElemOff http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... p http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... i http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... = liftM http://hackage.haskell.org/package/base-4.12.0.0/docs/src/GHC.Base.html#lift... (`compare` (1::HTYPE_INT)) $ http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... peekElemOff (castPtr p) i pokeElemOff http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... p http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... i http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... x http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... = pokeElemOff http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... (castPtr http://hackage.haskell.org/package/base-4.12.0.0/docs/src/GHC.Ptr.html#castP... p http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h...) i http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h... (fromIntegral (fromEnum x http://hackage.haskell.org/package/base-4.12.0.0/docs/src/Foreign.Storable.h...)::HTYPE_INT)