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-- Exercise 3-i
-- Which of these types are `Functor`s? Give instances for the ones that are.
-- `T1` is a `Functor`:
newtype T1 a
= T1 (Int -> a)
instance Functor T1 where
fmap f (T1 g) = T1 $ f <$> g
newtype T2 a
= T2 (a -> Int)
newtype T3 a
= T3 (a -> a)
newtype T4 a
= T4 ((Int -> a) -> Int)
-- `T5` is a `Functor`:
newtype T5 a
= T5 ((a -> Int) -> Int)
instance Functor T5 where
fmap f (T5 g) = T5 $ \f' -> g $ f' . f
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