Joshua Backfield [Joshua Backfield] - Becoming Functional

This chapter was intended as a high-level overview of the important concepts of functional programming. At this point youre probably wondering how can I actually get started using these concepts? As we go through this book, well look at how to implement these features in your code.

In each chapter, Ill introduce a concept, and then well work to refactor and implement it in our example code for the ficticious company XXY. The examples have no driver code. I assume that everyone reading this book can write simple Java main() functions to test out the code were writing. Im doing this for two reasons.

First, I really want you to write the code and test it out yourself; just reading the examples isnt going to help you understand the concepts or help you become a better functional programmer.

Second, I want to draw attention away from the driver code. Sometimes, when writing more extraneous code to actually call the code that were refactoring, we either forget to refactor the driver code or tend to write too much. Would it really be useful to create a set of driver code to create 10 or 20 Customer objects?

Each language example is compilable and runnable. The language examples will not rely on external packages. One of the things I truly dislike about some concept books or language books is that normally the author will push you to download third-party packages. In contrast, the goal of this book is to teach you how to deal with functional concepts using the core language.

Although most functional programming books present immutable variables first, were going to start with first-class functions. My hope is that as you read through this chapter, you will see ways in which you could start using some of these ideas at your job tomorrow.

First-class functions are functions treated as objects themselves, meaning we can pass a function as a parameter to another function, return a function from a function, or store a function in a variable. This is one of the most useful features in functional programming, and also one of the most difficult to learn to use effectively.