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sleexyz/Functor.hs

Created August 5, 2016 01:31
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Functor.hs
-- How do we make a tuple that's functorial over the first parameter?
-- We can't!
data Tup a b = Tup a b
instance Functor (Tup a) where
fmap f (Tup x y) = Tup x (f y)
instance Functor (Tup a) where
fmap f (Tup x y) = Tup x (f y)
-- -- Invalid Haskell, unfortunately:
-- instance Functor (\a -> (a,b)) where
-- fmap f (x,y) = (f x, y)
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