:: (x -> y) -> (p -> q) -> Either x p -> Either y q package:base

bimap :: Bifunctor p => (a -> b) -> (c -> d) -> p a c -> p b d
base Data.Bifunctor
Map over both arguments at the same time. 
bimap f g ≡ first f . second g

Examples

>>> bimap toUpper (+1) ('j', 3)
('J',4)

>>> bimap toUpper (+1) (Left 'j')
Left 'J'

>>> bimap toUpper (+1) (Right 3)
Right 4
bimapDefault :: Bitraversable t => (a -> b) -> (c -> d) -> t a c -> t b d
base Data.Bitraversable
A default definition of bimap in terms of the Bitraversable operations. 
bimapDefault f g ≡
runIdentity . bitraverse (Identity . f) (Identity . g)