Becoming Functional

Preface

Although not a new concept, functional programming has started to take a larger hold in the programming community. Features such as immutable variables and pure functions have proven helpful when we have to debug code, and higher-order functions make it possible for us to extract the inner workings of functions and write less code over time. All of this leads to more expressive code.

Who Is This Book For?

I wrote this book for anyone who is interested in functional programming or is looking to transition from an imperative style to a functional one. If you’ve been programming in an imperative or object-oriented style, my hope is that you’ll be able to pick up this book and start learning how to code in a functional one instead.

This book will teach you how to recognize patterns in an imperative style and then walk you through how to transition into a more functional one. We will approach this by looking at a fictional company called XXY and look at their legacy code. We’ll then refactor its legacy code from an imperative style into a functional one.

We’re going to use a few different languages throughout this book:

Java

I assume that you are familiar with the Java syntax. The version used in this book is 1.7.0.

Groovy

Using this language, we can keep most of our existing Java syntax; this helps us begin our transition into a fully functional language. I’ll explain the main parts of the Groovy syntax as they are needed. The version used in this book is 2.0.4.

Scala

This ...