Basics concepts

Functional programming is composed of a few well-defined concepts. A short introduction of these concepts will follow and, later on, each concept will be covered in depth, in the next chapters.

First-class and higher-order functions

The most foundational concept of functional programming is first-class functions. A programming language with support for first-class functions will treat functions as any other type; such languages will allow you to use functions as variables, parameters, returns, generalization types, and so on. Speaking of parameters and returns, a function that uses or returns other functions is a higher-order function.

Kotlin has support for both concepts.

Let's try a simple function ...