If you’ve had trouble trying to learn Functional Programming (FP),you’re not alone. In this book, Alvin Alexander — author of the Scala Cookbook for O’Reilly, the Scala Book for the official Scala website, and former teacher of Java and Object-Oriented Programming (OOP) classes — writes about his own problems in trying to understand FP, and how he finally conquered it.

The first thing he learned is that experienced FP developers are driven by two goals: to use only immutable values, and write only pure functions. What he later learned is that they have these goals as the result of another larger goal (or mental model): they want all of their code to look and work just like algebra.

While that sounds simple, it turns out that these goals require them to use many advanced Scala features — which they often use all at the same time. As a result, their code can look completely foreign to novice FP developers. As Mr. Alexander writes, “When you first see their code it’s easy to ask, ‘Why would anyone write code like this?’”