Hello,

I tried to compile my project with GHC 8 (from HEAD).

And I got

• Overlapping instances for aeson-0.11.1.0:Data.Aeson.Types.Class.ToJSON
...
arising from a use of ‘serve’
Matching instances:
two instances involving out-of-scope types
instance aeson-0.11.1.0:Data.Aeson.Types.Class.ToJSON b =>
aeson-0.11.1.0:Data.Aeson.Types.Class.ToJSON
(Data.Tagged.Tagged a b)
-- Defined in ‘aeson-0.11.1.0:Data.Aeson.Types.Instances’
instance forall k x (r :: k).
aeson-0.11.1.0:Data.Aeson.Types.Class.ToJSON x =>
aeson-0.11.1.0:Data.Aeson.Types.Class.ToJSON
(Data.Tagged.Tagged r x)

One of instances should be removed probably.

I suppose that instance for removing should be instance in Data.Tagged.

But version in Aeson should be PolyKinded.

What do you think?

Best regards,

Dmitry