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-- Pattern synonyms
{-# LANGUAGE PatternSynonyms, GADTs #-}
module Main where
data T a where
MkT :: (Eq b) => a -> b -> T a
pattern P x y <- MkT x y
f :: T Bool -> Bool
f (P x y) = x && y == y
data Crazy = Crazy
instance Eq Crazy where
_ == _ = False
main = do
print (f $ MkT True True)
print (f $ MkT True Crazy)
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