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module Validation where
import Test.QuickCheck (Arbitrary(..), frequency)
import Test.QuickCheck.Checkers
data Validation e a =
Failure e
| Success a
deriving (Eq, Show)
instance Functor (Validation e) where
fmap f (Success x) = Success $ f x
fmap f (Failure x) = Failure x
instance Monoid e => Applicative (Validation e) where
pure = Success
(Failure x) <*> (Success _) = Failure x
(Success _) <*> (Failure x) = Failure x
(Failure f) <*> (Failure y) = Failure $ mappend f y
(Success f) <*> (Success y) = Success $ f y
instance (Arbitrary a, Arbitrary e) => Arbitrary (Validation e a) where
arbitrary = frequency [(1, Failure <$> arbitrary),
(5, Success <$> arbitrary)]
instance (Eq a, Eq e) => EqProp (Validation e a) where
(=-=) = eq
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