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{-# LANGUAGE UnboxedSums #-}
{-# LANGUAGE PatternSynonyms #-}
module Main where
type Maybe' t = (# t | () #)
pattern Just' :: a -> Maybe' a
pattern Just' x = (# x | #)
pattern Nothing' :: Maybe' a
pattern Nothing' = (# | () #)
foo x = case x of
Nothing' -> putStrLn "nothing"
Just' _ -> putStrLn "just"
main = do
putStrLn "Nothing'"
foo Nothing'
putStrLn "Just'"
foo (Just' "hello")
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