Reactive Programming is all about building responsive applications. There are several ways in which we can make our applications reactive. Some are old ideas: dataflow programming, electronic spreadsheets, and the Observer pattern are all examples. But CES in particular has become popular in recent years.

CES aims to bring to Reactive Programming the declarative way of modeling problems that is at the core of Functional Programming. We should worry about what and not about how.

In next chapters, we will learn how we can apply CES to our own programs.