Part 1. Think functionally
It’s highly probable that most of your experience building professional applications has been with an object-oriented language. You may have heard or read about functional programming in other books, blogs, forums, and magazine articles, but you’ve probably never written any functional code. Don’t worry; this is to be expected. I’ve done most of my development in an object-oriented environment as well. Writing functional code isn’t difficult, but learning to think functionally and letting go of old habits is. The primary goal of part 1 of this book is to lay the foundation for and prepare your mind to embrace the functional techniques discussed in parts 2 and 3.
Chapter 1 discusses what functional programming is and the mindset you need to embrace it; it also introduces some of the most important techniques based on pure functions, immutability, side effects, and referential transparency. These form the backbone of all functional code and will help you transition into functional more easily. Also, these will be the guiding principles that set the stage for many of the design decisions we make in the following chapters.