Michal Plachta - Grokking Functional Programming

Hello! Thanks for purchasing Grokking Functional Programming. Ive spent the last decade talking with programmers about the approach to programming, its maintainability, and how functional programming concepts are slowly being adopted by mainstream languages. Many of those professional developers say its still very difficult to learn functional concepts from existing sources, which are either too simplistic or too complex. Thats the gap this book is trying to fill. It aims to provide a step-by-step practical guide for programmers who want to get the full picture of fundamental functional programming concepts.

People learn best from examples, and thats why this book is heavy with them. Theory always comes second. After finishing this introductory book, youll be able to write fully featured programs using functional programming and comfortably dive into its theoretical foundations.

Youll get the most benefit from this book if youve already created some non-trivial applications using an imperative object-oriented language like Java or Ruby. Its a big plus if youve worked on a team who struggled with lots of bugs and maintainability issues, because this is where functional programming shines the most.

I hope youll enjoy reading the chapters and solving the exercises as much as I enjoyed writing them. Thanks again for your interest in the book!

Micha Pachta

Id like to first of all thank the Scala community for its continuous pursuit of tools and techniques that help build maintainable software. All of the ideas presented in the book are the result of countless hours of code reviews, discussions, multiple back-and-forth blog articles, hot-take presentations, and production outage postmortems. Thank you all for your passion.

Id like to thank my family, especially my wife Marta, for supporting me during the writing of this book with huge amounts of encouragement and love. Many thanks go to my wonderful kids, Wojtek and Ola, for making sure I dont sit at the computer for too long.

This book has been the work of many people. Id like to thank the staff at Manning: Michael Stephens, acquisitions editor; Bert Bates, editor; Jenny Stout, development editor; Josh White, technical development editor; Christian Berk, copy editor; Keri Hales, production editor; Ubaldo Pescatore, technical proofreader; Katie Tennant, proofreader; and all of the behind-the-scenes folks who helped get this book into print.

To all the reviewers: Ahmad Nazir Raja, Andrew Collier, Anjan Bacchu, Charles Daniels, Chris Kottmyer, Flavio Diez, Geoffrey Bonser, Gianluigi Spagnuolo, Gustavo Filipe Ramos Gomes, James Nyika, James Watson, Janeen Johnson, Jeff Lim, Jocelyn Lecomte, John Griffin, Josh Cohen, Kerry Koitzsch, Marc Clifton, Mike Ted, Nikolaos Vogiatzis, Paul Brown, Ryan B. Harvey, Sander Rossel, Scott King, Srihari Sridharan, Taylor Dolezal, Tyler Kowallis, and William Wheeler, thank you; your suggestions helped make this a better book.

Who should read this book

The book assumes that the reader has at least one year of commercial experience developing software using a mainstream object-oriented programming language like Java. Examples use Scala as the teaching language, but this is not a Scala book. No prior knowledge of Scala or functional programming is required.

How this book is organized: A road map

The book is divided into three parts. The first part lays the foundation. We will learn tools and techniques that are ubiquitous in functional programming (FP). In chapter 1, we will discuss how to learn FP with this book. In chapter 2, we will show the difference between pure and impure functions. In chapter 3, we will introduce the immutable value. Finally, in chapter 4, we will show how pure functions are just immutable values and demonstrate all the superpowers that we get from this fact.

In the second part of the book, we will use only immutable values and pure functions to solve real-world problems. In chapter 5, we will introduce the most important function in FP and show how it helps in building sequential values (and programs) in a concise and readable way. In chapter 6, we will learn how to build sequential programs that may return errors. We will use chapter 7 to learn about functional software design. Chapter 8 will teach you how to deal with an impure, external, side-effectful world in a safe and functional way. Then, we will introduce streams and streaming systems in chapter 9. We will build streams of hundreds of thousands of items using the functional approach. In chapter 10, we will finally create some functional and safe concurrent programs.