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-- Form.hs
module T10421a_Form where
import Control.Applicative
data FormResult a = FormMissing
| FormFailure [String]
| FormSuccess a
instance Functor FormResult where
fmap _ FormMissing = FormMissing
fmap _ (FormFailure errs) = FormFailure errs
fmap f (FormSuccess a) = FormSuccess $ f a
instance Applicative FormResult where
pure = FormSuccess
(FormSuccess f) <*> (FormSuccess g) = FormSuccess $ f g
(FormFailure x) <*> (FormFailure y) = FormFailure $ x ++ y
(FormFailure x) <*> _ = FormFailure x
_ <*> (FormFailure y) = FormFailure y
_ <*> _ = FormMissing
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