import Control.Lens


-- from Control.Error
hush :: Either e a -> Maybe a
hush (Left _) = Nothing
hush (Right a) = Just a

-------------------------------------------------------------------------------
data Lossy e a b = Lossy {
    previewE :: a -> Either e b
  , reviewE :: b -> a
  }


lossy :: (b -> a) -> (a -> Either e b)-> Lossy e a b
lossy = flip Lossy


hushLossy :: Lossy e a b -> Prism' a b
hushLossy l = prism' (reviewE l) (hush . (previewE l))


-------------------------------------------------------------------------------
newtype MyInt = MyInt Int deriving (Show)


data MyIntError = TooBig
                | TooSmall
                deriving (Show)


myIntLossy :: Lossy MyIntError Int MyInt
myIntLossy = lossy toI fromI
  where
    toI (MyInt i) = i
    fromI i
      | i < 0 = Left TooSmall
      | i > 10 = Left TooBig
      | otherwise = Right (MyInt i)


useLikePrism :: Either MyIntError MyInt
useLikePrism = previewE myIntLossy 42


useAsPrism :: Maybe MyInt
useAsPrism = 42 ^? hushLossy myIntLossy