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theqp/After.hs Secret

Created October 7, 2021 16:03
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After.hs
class Fold a where
fold :: a
instance Fold (b -> (a -> b) -> Maybe a -> b) where
fold nothing just = \case
Nothing -> nothing
Just a -> just a
instance Fold ((a -> c) -> (b -> c) -> Either a b -> c) where
fold l r = \case
Left a -> l a
Right b -> r b
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