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{-# LANGUAGE TypeFamilies, GeneralizedNewtypeDeriving, StandaloneDeriving, FlexibleInstances #-}
-- Test Trac #2856
module T2856 where
import Data.Ratio
----------------------
class C a where
data D a
instance C Bool where
newtype D Bool = DInt Int deriving (Eq, Show, Num)
instance C a => C [a] where
newtype D [a] = DList (Ratio a) deriving (Eq, Show, Num)
----------------------
data family W a
newtype instance W Bool = WInt Int deriving( Eq, Show )
newtype instance W [a] = WList (Ratio a) deriving( Eq, Show )
deriving instance Num (W Bool)
deriving instance (Integral a, Num a) => Num (W [a])
-- Integral needed because superclass Eq needs it,
-- because of the stupid context on Ratio
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