Monad.Either

Utilites to work with Either data type.

Documentation

module Data.Either

maybeToLeft :: r -> Maybe l -> Either l r

Maps Maybe to Either wrapping default value into Right.

>>> maybeToLeft True (Just "aba")
Left "aba"
>>> maybeToRight True Nothing
Right True

maybeToRight :: l -> Maybe r -> Either l r

Maps Maybe to Either wrapping default value into Left.

>>> maybeToRight True (Just "aba")
Right "aba"
>>> maybeToRight True Nothing
Left True

leftToMaybe :: Either l r -> Maybe l

Maps left part of Either to Maybe.

>>> leftToMaybe (Left True)
Just True
>>> leftToMaybe (Right "aba")
Nothing

rightToMaybe :: Either l r -> Maybe r

Maps right part of Either to Maybe.

>>> rightToMaybe (Left True)
Nothing
>>> leftToMaybe (Right "aba")
Just "aba"

whenLeft :: Applicative f => Either l r -> (l -> f ()) -> f ()

Applies given action to Either content if Left is given.

whenLeftM :: Monad m => m (Either l r) -> (l -> m ()) -> m ()

Monadic version of whenLeft.

whenRight :: Applicative f => Either l r -> (r -> f ()) -> f ()

Applies given action to Either content if Right is given.

whenRightM :: Monad m => m (Either l r) -> (r -> m ()) -> m ()

Monadic version of whenRight.