Re: leftToMaybe/rightToMaybe

Ivan Lazar Miljenovic wrote:

On 7 August 2013 14:06, Erik de Castro Lopo wrote:

...

Christopher Done wrote:

...

How about popping these in Data.Either?

-- | Maybe get the left side of an Either. leftToMaybe :: Either a b -> Maybe a leftToMaybe = either Just (const Nothing)

-- | Maybe get the right side of an Either. rightToMaybe :: Either a b -> Maybe b rightToMaybe = either (const Nothing) Just

+1

And while we're at it:

isLeft :: Either a b -> Bool isLeft (Left _) = True isLeft (Right _) = False

isRight :: Either a b -> Bool isRight (Left _) = False isRight (Right _) = True

If we're starting to add functions to Data.Either, I've often used something like this:

mapEither :: (l -> l') -> (r -> r') -> Either l r -> Either l' r' mapEither fl fr = either (Left . fl) (Right . fr)

+1 Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/