Data.Either.Extra

Documentation

module Data.Either

isLeft :: Either l r -> Bool

Test if an Either value is the Left constructor. Provided as standard with GHC 7.8 and above.

isRight :: Either l r -> Bool

Test if an Either value is the Right constructor. Provided as standard with GHC 7.8 and above.

fromLeft :: Either l r -> l

The fromLeft function extracts the element out of a Left and throws an error if its argument is Right. Much like fromJust, using this function in polished code is usually a bad idea.

 \x -> fromLeft (Left  x) == x
 \x -> fromLeft (Right x) == undefined

fromRight :: Either l r -> r

The fromRight function extracts the element out of a Right and throws an error if its argument is Left. Much like fromJust, using this function in polished code is usually a bad idea.

 \x -> fromRight (Right x) == x
 \x -> fromRight (Left  x) == undefined

fromEither :: Either a a -> a

Pull the value out of an Either where both alternatives have the same type.

 \x -> fromEither (Left x ) == x
 \x -> fromEither (Right x) == x