day 12 

On day 11 we started reading Jeremy Gibbons’s Datatype-Generic Programming. We saw the creative use of Fix and Bifunctor,

When we moved on to The Essence of the Iterator Pattern, we found that Cats uses Const to represent monoidal applicatives like Int, but it’s currently missing a way to compose applicative functions.

We started with a datatype called Tuple2K that represents a pair of F[A] and G[A], then we also added AppFunc that represents applicative functions. #388