Unboxed Vectors of newtype'd values

[Roman Leshchinskiy]

Andres Löh wrote:
>
> Yes, because these are superclasses of Unbox. So can't you simply say
> this:
>
>> newtype Foo = Foo Int
>>   deriving (Eq, Show, Unbox, M.MVector MVector, G.Vector Vector)

I don't think this should work. This is the basic set up:

class G.Vector v a where
  basicLength :: v a -> Int
  ...

data family Vector a

newtype instance Vector Int = V_Int ...

instance G.Vector Vector Int where
  basicLength (V_Int ...) = ...
  ...

I don't understand what GeneralizedNewtypeDeriving does with
deriving(G.Vector Vector) in this situation but it can't possibly do
anything sensible without a data instance Vector Foo. The fact that it
doesn't fail is just a bug, IMO.

Roman