In this chapter, we covered the concept of functional data structures and explored examples of data structures implemented in a functional way, such as Semigroup, Monoid, BST, linked list, stack, and lazy list.

Even though none of the data structures are complete, they serve as structures that present functional programming paradigms and techniques. It would also be beneficial to examine the performance of any of these data structures.

In the following chapter, we will cover the importance of immutability by examining its benefits. We will also examine an example of a mutable versus an immutable implementation as well as the means to get and set immutable objects in a functional way, such as copy constructors and lenses.