BifunctorUsage
A Bifunctor is very similar to a Functor, which you are hopefully
already familiar with. Whereas a Functor operates on a * → * and
has a single operation map which takes a function from A => B to
map a F[A] to a F[B], a Bifunctor operates on a , → * and has a
single operation bimap which takes two functions: A => C and a
B => D to map a F[A,B] to a F[C,D]:
def bimap[A, B, C, D](fab: F[A, B])(f: A => C, g: B => D): F[C, D]
some examples of common types for which we have Bifunctor instances are Either, Validation, /, Tuple2