Lesson 5: Two maps in one
- Coming up
We spent the previous four lessons on understanding the
Functor typeclass as well as type constructors and functors more generally; we also discussed the laws of the
Functor class and how (and why) to check them with the
hedgehog testing library.
fmap is a useful tool, but with some types, such as those constructed by
(,), we may want the ability to
fmap over either side, or both sides. This lesson introduces a typeclass called
Bifunctor for just those times.