Functional programming paradigms are slightly different than that of Object-oriented programming (OOP). It focuses on the use of declarative and expressive programs and immutable data rather than on statements. The definition of functional programming says functional programming is a programming system that relies on structuring the program as the evaluation of mathematical functions with immutable data, and it avoids state-change. It is a declarative programming paradigm that suggests use of small, reusable declarative functions.

We have seen the definition of functional programming; now, don't you want to delve into its definition and see what it exactly means? Do all languages support functional programming? If not, then which languages does and what about Kotlin? What exactly does reactive programming have to do with functional programming? And, finally, what do we need to learn, for functional programming?

In this chapter, we will cover the following topics:

• Getting started with functional programming
• Relationship of functional programming with reactive programming
• The path breaking feature of Kotlin–coroutines