Functional Programming with C#

After decades of relative obscurity, functional programming is finally coming into its own. With concise, easy-to-read code that supports asynchronous, concurrent processing, aspects of functional programming have begun to appear in several traditionally object-oriented languages such as C# and Java. This practical book shows C# programmers how to use functional programming features without having to navigate an entirely new language.

Because of the shared runtime environment common to C# and F# languages, it’s possible to use most of F#’s functional features in C# as well. Author Simon J. Painter explains how you can write functional code in C# right away, without having to install dependencies or features newer than .NET 3. You’ll learn why functional programming concepts can bring immediate benefit to your work.

• Learn what functional programming is and how it originated
• Discover features of the functional paradigm using a more familiar language
• Start coding functionally in C# right away, without relying on third-party libraries
• Write code that’s more robust, less error prone, and easier to test
• Examine less conventional ways to look at structures available in C#
• Explore the practicalities of using functional C# in a business environment

Table of Contents

Chapter 1. Introduction

Part I. What Are We Already Doing?

Chapter 2. What Can We Do Already?

Chapter 3. Functional Coding in C# 7 and Beyond

Chapter 4. Work Smart, Not Hard with Functional Code

Part II. Into the Belly of the Functional

Chapter 5. Higher-Order Functions

Chapter 6. Discriminated Unions

Chapter 7. Functional Flow

Chapter 8. Currying and Partial Application

Chapter 9. Indefinite Loops

Chapter 10. Memoization

Part Ill. And Out the Other Side

Chapter 11. Practical Functional C#

Chapter 12. Existing Functional Programming Libraries in NuGet

Chapter 13. The Martian Trail

Chapter 14. Conclusion

This book introduces all the fundamental concepts of FP, demonstrates their benefits, and describes how they might be achieved in C#—not just for your own hobby programming, but with a real eye toward bringing immediate benefit to your work life as well.

These benefits include things such as the following:

• Code that is cleaner, tidier, and easier to read
• An easier-to-maintain codebase
• Applications that are significantly less likely to suffer from unhandled exceptions and their unpredictable consequences
• A codebase that’s easier to write automated unit tests for

All this and more!

Who Should Read This Book?

This book is intended for developers—whether professional, student, or hobbyist—who already have a basic grounding in C#. You don’t need to be an expert but do need to be familiar with the basics and feel comfortable putting together at least a relatively simply C# application.

Some more advanced .NET topics are covered, but I’ll provide explanations when they come up.

This book has been written with a few categories of people in mind:

• Those of you who have learned the basics of C# but want to find ways to take your learning further via more advanced techniques for writing better, more robust code.
• .NET developers who have heard of FP and perhaps even know what it is, but want to know how to get started writing code that way in C#.
• F# developers looking for ways to keep using the functional toys you’re used to.
• Those migrating to .NET from another functional, or functional-supporting, language (like Java).
• Anyone who really, truly loves coding. If you spend all day writing code in the office, then come home to write more for fun, this book is probably for you.

About the Author

Simon J. Painter has been developing professionally for far, far too long now (well, since 2005) and has worked with every version of .NET ever released (including Compact Framework – remember that?) in around a dozen different industries. As well as his day job, he also appears regularly at user groups and conferences to give talks on Functional Programming and general .NET topics. Before becoming a professional, Simon had been a coding enthusiast since he was old enough to read his Dad’s copy of the Sinclair ZX Spectrum BASIC handbook. Besides code, he loves Music, Cryptic Crosswords, Fighting Fantasy Gamebooks and far more coffee than is likely to be healthy for him. He lives in a small town in the UK, with his wife and children.