The Haskell' committee decided to remove datatype contexts from the language:
http://www.haskell.org/pipermail/haskell-prime/2011-January/003335.html
(though this doesn't seem to be in the Report yet.)
In the base package there are 4 of these:
Data/Complex.hs:data (RealFloat a) => Complex a
GHC/Arr.lhs:data Ix i => Array i e
GHC/Real.lhs:data (Integral a) => Ratio a = !a :% !a deriving (Eq)
Control/Arrow.hs:newtype ArrowApply a => ArrowMonad a b = ArrowMonad (a () b)
As far as I know, removing them won't break any code that compiles now,
so let's do it.
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