This chapter started by explaining why functional programming matters, and then it introduced key paradigms in functional programming. Furthermore, it introduced the basics of the Swift programming language with code examples. At this point, we should have a broad view of functional programming concepts and the Swift programming language. All the topics in this chapter will be covered in detail in upcoming chapters.

We will begin to dive deeper into these topics by functions as they are the most essential building blocks in functional programming. Therefore, the following chapter will explain functions and give examples for pure, first-class, higher-order, and nested functions. Also, it will explain slightly more advanced topics such as memoization, function currying, and composition.