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{-# OPTIONS -fwarn-incomplete-patterns -fwarn-overlapping-patterns -Werror #-}
module T322 where
instance (Num a) => Num (Maybe a) where
(Just a) + (Just b) = Just (a + b)
_ + _ = Nothing
(Just a) - (Just b) = Just (a - b)
_ - _ = Nothing
(Just a) * (Just b) = Just (a * b)
_ * _ = Nothing
negate (Just a) = Just (negate a)
negate _ = Nothing
abs (Just a) = Just (abs a)
abs _ = Nothing
signum (Just a) = Just (signum a)
signum _ = Nothing
fromInteger = Just . fromInteger
f :: Maybe Int -> Int
f 1 = 1
f Nothing = 2
f _ = 3
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