Learn Functional Programming Without Fear: A Java/Kotlin/OOP teacher takes you to FP, ZIO, and Cats Effect

(Note: This book was previously named Learn Functional Programming Without Fear.)

Would you like to be able to learn what the fuss is about functional programming (FP), without having to learn the abstract concepts in category theory?

And would you like to understand world-class FP libraries like ZIO and Cats Effect that power high-performance, massively-parallel websites like Caesars and Disney Streaming?

To get you started in that direction, this small, easy to read book from the Scala/FP community’s leading author has one goal: When you finish the book you should be able to look at the documentation for the ZIO and Cats Effect websites and think, “Aha, I know WHAT they’re doing, and WHY they’re doing it.”

This book takes you to the cusp of using those FP libraries, and once you have this foundational knowledge, everything else in FP is just a matter of learning the details of each library.

The Approach

Alvin Alexander “discovered” this teaching technique while he was writing the 2nd Edition of the Scala Cookbook. Thanks to the new approaches in the ZIO library — which were released at that time — he found that if you really learn the Option, Try, and Either data types, they naturally lead to the ‘IO’ data type you hear about in the FP world: The ZIO type in the ZIO library, and IO in Cats Effect.

A huge benefit of this approach is that you don’t have to spend time learning category theory, monoids, functors, monads, etc. Instead, you just focus on pragmatic knowledge and writing code. Each small lesson is four pages on average, and each one adds a new piece of knowledge, until at the end of the book you’re writing FP code using ZIO.

If you go right from the book to the ZIO 2 documentation you should know what they’re doing and why they’re doing it.

And if you still want to learn category theory at this point, you’re more than welcome to. It won’t hurt, but as Alvin shows, it’s not necessary.

About the Author

Alvin Alexander is the author of:
Functional Programming, Simplified (a 700+ page book), one of the best-selling, highly-rated FP books of all time
Two editions of the Scala Cookbook (both over 700 pages)
Learn Scala 3 The Fast Way!
A primary author of the Scala 3 Book on the official Scala website
alvinalexander.com, which receives millions of page-views
Alvin writes in a simple, conversational style, as though he’s sitting next to you in a pair programming session, or mentoring you in a small classroom.

Written for OOP Developers

If you’re an OOP developer who uses programming languages like Java or Kotlin, Alvin understands your background. Alvin is a former Java/OOP instructor and mentor, and uses Kotlin for Android apps, and Flutter/Dart for iOS/Android apps. (He has also used Python, Swift, Rust, Ruby, and other languages.)

The Book’s Path

The book starts with a discussion of the Java/OOP code Alvin wrote (and taught) for 15 years. He then shows how to solve programming problems using these techniques:
Pure functions
Immutable (algebraic) variables
Immutable data structures
After comparing this code to his previous Java/OOP code, it’s off to the races as he adds in:
Expression-oriented programming (EOP)
Functional error handling with Option, Try, and Either
After that, he shows how these techniques naturally lead to the concepts found in the ZIO and Cats Effect libraries. As Alvin writes in Functional Programming, Simplified, if you had been interested in these techniques many years ago, you might have invented FP yourself.