Haskell Cookbook

How to do it...

1. Open src/Main.hs. 
2. Import the Data.Either module:

        import Data.Either

3. Define safe division, handling the division by zero case:

        safeDiv :: Either String Int -> Either String Int -> Either          String Int        safeDiv (Left e) _ = Left e  -- Any Left _ is an error, we         produce the same        safeDiv _ (Left e) = Left e  -- error as a result.        safeDiv (Right i) (Right j) | j == 0 = Left "Illegal Operation:          Division by Zero"        safeDiv (Right i) (Right j) = Right (i `div` j)

4. Use safe division in the main function to illustrate usage of Either:

        main :: IO ()        main = do        let i = Right 10 :: Either String Int        j = Right 2 :: Either String Int        z = Right 0 :: Either String Int        putStrLn $ "Safe division : 10 / 2 = " ++ (show $ safeDiv i j) putStrLn ...