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bitwombat/Page475_trimmed.hs

Last active July 20, 2019 05:32
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Page475
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Page475_trimmed.hs
module Page475 where
-- Ex 5
either' :: (a -> c) -> (b -> c) -> Either a b -> c
either' f g eab =
case eab of
Left a -> f a
Right b -> g b
-- Ex 6
rightVal :: Either a b -> b
rightVal (Right x) = x
eitherMaybe'' :: (b -> c) -> Either a b -> Maybe c
eitherMaybe'' f eab =
case eab of
Left _ -> Nothing
_ -> Just (either' (f . g (rightVal eab)) f eab)
where
g :: b -> a -> b
g b a = b
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