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module T17722A (Validation(..)) where
data Validation e a
= Failure e
| Success a
instance Functor (Validation e) where
fmap _ (Failure e) = Failure e
fmap f (Success a) = Success (f a)
(<.>) :: Semigroup e => Validation e (t -> a) -> Validation e t -> Validation e a
Failure e1 <.> b = Failure $ case b of
Failure e2 -> e1 <> e2
Success _ -> e1
Success _ <.> Failure e = Failure e
Success f <.> Success x = Success (f x)
instance Semigroup e => Applicative (Validation e) where
pure = Success
(<*>) = (<.>)
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