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{-# LANGUAGE GADTs, GeneralizedNewtypeDeriving #-}
-- See Trac #1251 and the comments
-- Note [Pruning dead case alternatives] in types/Unify.lhs
module Main( main ) where
data T a where MkT :: T Int
class C a where ic :: T a
instance C Int where ic = MkT
newtype A = MkA Int deriving( C )
-- axiom CoA : A ~ Int
-- Hence C Int ~ C A
-- instance C A where
-- ic :: T A
-- ic = MkT
icA = ic :: T A -- There are no (non-bot) values of this type
main = print (icA `seq` "ok")
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