How to extract a nested unbalanced structure

normalizer.hs

-- I was thinking on how to normalize a structure like
-- (Either String (Either String Int)) into
-- Either String Int

-- my first attempt was to pattern match
normalizer :: (Either String (Either String Int)) -> Either String Int
normalizer n = do
    case n of 
        Left l  -> Left l
        Right r -> r
        
-- but that somehow liked unhaskellish

-- so I tried this
normalizer' :: (Either String (Either String Int)) -> Either String Int
normalizer' n = either Left id n

-- much better!

-- the empiphany is this
-- a) Data constructors a functions too - Left :: a -> Left a
-- b) if one wants to pipe a value to a function an get the same input back. id is your friend because 
--    id :: a -> a

r = normalizer $ Right (Right 10)
l = normalizer $ Left "Oh my"

r' = normalizer' $ Right (Right 10)
l' = normalizer' $ Left "Oh my"

You can also use join from Control.Monad.

> join $ Right (Right 10)
Right 10
> join $ Left "oh noes"
Left "oh noes"

@jstepien - nice that join