Mastering Functional Programming

Applicative

Knowing how to compose computations in sequence is a basic skill that enables procedural programming to take place. This is something that we rely upon by default when we use imperative programming languages. When we write two statements in sequence, we implicitly mean that these two statements are supposed to be executed one after another.

However, sequential programming is not capable of describing all the programming situations, especially if you're working in the context of an application that is supposed to run in parallel. There may be lots of situations where you may want computations composed in parallel. This is exactly where the Applicative type class comes into play.