Lesson 3: Sequencing effects

Previously we looked at the connection between <*> and liftA2, their connection to fmap, the pure function, and the monoidal structure of applicatives. We will still want to give some closeup attention to a few other applicatives, especially functions and lists, but this lesson will focus on the other operators in the typeclass (<* and *>) before we move on to those. While you almost never need to implement them yourself – because the compiler can derive them from your implementations of pure and <*> (or pure and liftA2) – they are useful, yet often ignored. They are useful enough to deserve at least one lesson of their own.