Applied Functional Programming in Scala

Functional programming is transforming how we build robust, scalable, and maintainable software by prioritizing clarity and predictability. It emphasizes what to compute by defining expressions that map values to other values, and focuses on how to achieve a result through a sequence of statements that change program state.

This book explores core functional principles like immutability, pure functions, and referential transparency. You will gain a deep understanding of the mathematical underpinnings through category theory concepts like Functors and Monads, and then apply these practically using Scala functional features and leading libraries such as Cats and ZIO. The book also covers handling effects and I/O, advanced functional patterns, and using specialized tools to build functional web, database, and streaming solutions. With real examples and patterns, it shows how these ideas can simplify code, improve testability, and increase system resilience.

By the end of this book, you will have a theoretical understanding and practical proficiency in building high-quality, maintainable applications using functional programming in Scala.

WHAT YOU WILL LEARN
● Implement Scala higher-order functions, currying, and Option/Either.
● Understand Functors, Monads, and their category theory relevance.
● Utilize Cats type classes for extensible functional programming.
● Build scalable applications using FP patterns.
● Manage side-effects and I/O functionally using effect systems.
● Real-world use of functional programming.

WHO THIS BOOK IS FOR
This book is for software engineers, developers, and architects seeking to write more composable, testable, and expressive code. Readers should have a basic understanding of programming concepts, but no prior functional language experience is required.

1. Fundamentals of Functional Programming
2. Implementation of Category Theory
3. Introduction to Scala
4. Understanding Cats
5. Understanding ZIO
6. Effects Implementation in Pure Way
7. Functional Pattern Implementation
8. Functional Tools
9. Web Implementation in Functional Way
10. DB Implementation in Functional Way
11. Functional Streams for Scala
12. Case Study on Functional Toy E-commerce Site

Virendra Kumar Mishra is a senior architect at SAP, with over 18 years of industry experience designing and delivering complex, scalable systems. He holds B.Tech in computer science, graduated in 2008, and has since built a career rooted in engineering principles, practical design, and continuous learning. He has worked with leading global IT organizations, including CenturyLink, Sapient, and now SAP, where he has led end- to-end 
implementations across domains. His core expertise lies in Java/Spring, Node.js, Scala, and other languages (Go, Haskell, etc) with reactive programming, and modern functional programming practices. His interest in category theory grew out of a desire to understand the deep abstractions behind code and how they can simplify real-world complexity when applied correctly.

Known among peers for his clear thinking and hands-on approach, Virendra also enjoys mentoring developers and engaging in architectural discussions that blend theory with practical trade-offs. He believes software development is not just about solving problems but about solving them elegantly.

Outside of work, he enjoys spending time with his family, reading about mathematics and philosophy, and taking long, reflective walks. This book is a culmination of years of experience, curiosity, and a passion for bridging the gap between abstract theory and pragmatic code.