Haskell Language Learning Note (bitraversable)

Bitraversable

class (Bifunctor t, Bifoldable t) => Bitraversable t where  bitraverse :: Applicative f => (a -> f c) -> (b -> f d) -> t a b -> f (t c d)  bitraverse f g = bisequenceA . bimap f gbisequenceA :: (Bitraversable t, Applicative f) => t (f a) (f b) -> f (t a b)bisequenceA = bitraverse id id

Bitraversable is a type class. Used primarily to traverse two-tuple data structures.

Either is a bitraversable.

instance Bitraversable Either where  bitraverse f _ (Left a) = Left <$> f a  bitraverse _ g (Right b) = Right <$> g b

(,) It's a bitraversable.

instance Bitraversable (,) where  bitraverse f g ~(a, b) = (,) <$> f a <*> g b

Const is a bitraversable.

instance Bitraversable Const where  bitraverse f _ (Const a) = Const <$> f a

Application bitraversable

Prelude Data.Bitraversable> bitraverse (\x -> [x, x+1]) (\x -> [x, x*2]) (Left 2)[Left 2,Left 3]Prelude Data.Bitraversable> bitraverse (\x -> [x, x+1]) (\x -> [x, x*2]) (Right 3)[Right 3,Right 6]Prelude Data.Bitraversable> bitraverse (\x -> [x, x+1]) (\x -> [x, x*2]) (2,3)[(2,3),(2,6),(3,3),(3,6)]Prelude Data.Bitraversable Control.Applicative> bitraverse (\x -> [x, x+1]) (\x -> [x, x*2]) (Const 2)[Const 2,Const 3]Prelude Data.Bitraversable> bisequenceA (Left [2,3])[Left 2,Left 3]Prelude Data.Bitraversable> bisequenceA (Right [2,3])[Right 2,Right 3]Prelude Data.Bitraversable> bisequenceA ([2,3],[4,5])[(2,4),(2,5),(3,4),(3,5)]Prelude Data.Bitraversable Control.Applicative> bisequenceA (Const [2,3])[Const 2,Const 3]

Haskell Language Learning Note (bitraversable)