Introducing Functional Programming Using C# : Leveraging a New Perspective for OOP Developers

Understand the power of C#, a multi-paradigm language. This book will help you learn, analyze, and harness the functional aspects of C# so you can create a better program. The book is divided into two parts. Part I starts with an overview of functional programming (FP). It covers the building blocks for FP: functions and immutability. You will learn about the built-in supports for FP, first- and higher-order functions (HOF), functional purity and side effects, different forms of immutability, and much more. Part II includes discussions on functional composition using pipelining and currying. It also explains how to handle temporal coupling and discusses partial functions and useful functional patterns (such as Map, Bind, Filter, and Fold). Author Vaskaran Sarcar takes you through functional exception-handling mechanisms and provides additional tips to make your programs more efficient. After reading the book, you will understand and be able to implement key aspects of FP. You will be able to produce better code (and refactor existing code) by combining the best techniques from both FP and object-oriented programming (OOP) paradigms. C# is a powerful programming language, is well accepted in the programming world, and helps you make a wide range of applications. These are the primary reasons it is continuously growing in popularity and is always in high demand. So, it is not a surprise that existing and upcoming developers (for example, college students and programming lovers) are curious to learn C# and want to create their applications using it. Many developers try to learn it in the shortest possible time frame and then claim they know C# well. In fact, many resources claim you can unlock the real power of C# in a day, a week, or a month. But is this true? I think not. Remember, I’m 14 years in and I’m still learning. What Will You Learn: Understand how the concepts of functional programming (FP) can be implemented using C# Refactor existing code (following the FP paradigm) to make it more readable, maintainable, and predictive Know how advanced features (such as delegates, lambdas, generics) can be used differently Understand how to efficiently use features such as lambda expressions and type inference as C# includes explicit language extensions to support functional programming Who This Book Is For: C# developers familiar with object-oriented programming (OOP) who want to harness the power of functional programming (FP) Table of Contents About the Author About the Technical Reviewers Acknowledgments Introduction How Is This Book Organized? Prerequisite Knowledge Who Is This Book For? Useful Software Guidelines for Using This Book Source Code Conventions Used in This Book Final Words Part I: Getting Familiar with Functional Programming Chapter 1: Functional Programming Overview C# Supports Multiple Paradigms Functions and Methods Are Equivalent in C# Q&A Session Important Characteristics of FP FP Treats Functions as First-Class Citizens Demonstration 1 Output Analysis FP Prefers Immutability Demonstration 2 Output Q&A Session Demonstration 3 Output Analysis FP Prefers Pure Functions Demonstration 4 Output Discussion of Side Effects Functions with I/O Are Side Effects Bad? Q&A Session FP Follows a Declarative Style Demonstration 5 Output Demonstration 6 Output Q&A Session Demonstration 7 Output FP vs. OOP FP Benefits Q&A Session Exercises Summary Solutions to Exercises E1.1 E1.2 E1.3 E1.4 E1.5 E1.6 E1.7 E1.8 Chapter 2: Understanding Functions Mathematical Background of Functions Mathematical Functions vs. C# Functions Representing Functions in C# Using Static Methods Demonstration 1 Output Simplifying the Code Q&A Session Using Delegates and Lambdas A Quick Review Demonstration 2 Output Additional Note Using a Dictionary Demonstration 3 Output Q&A Session Demonstration 4 Built-in Delegates Are Important Higher-Order Function Custom HOF Demonstration 5 Output Additional Note Built-in HOF Demonstration 6 Output Analysis First-Order Function Refactoring Impure Functions Program with Impurities Demonstration 7 Output Removing Impurities Demonstration 8 Output Additional Note Q&A Session Exercises Summary Solutions to Exercises E2.1 E2.2 E2.3 E2.4 E2.5 E2.6 Chapter 3: Understanding Immutability What Is Immutability? Immutable Objects in .NET Q&A Session Reviewing Mutable Types Programming with a Mutable Type Demonstration 1 Output Analysis The Path Toward Immutability Achieving External Immutability Demonstration 2 Output Enforcing Internal Immutability Demonstration 3 Output Better Code Using Modern Features Demonstration 4 Output Q&A Session More on Immutability Understanding Shallow Immutability Demonstration 5 Output Analysis Searching for a Solution Demonstration 6 Output Analysis Making a Better Solution Demonstration 7 Output Analysis Implementing Popsicle Immutability Demonstration 8 Output Analysis Q&A Session Exercises Summary Solutions to Exercises E3.1 E3.2 E3.3 E3.4 E3.5 Part II: Harnessing the Power of Functional Programming Chapter 4: Composing Functions Using Pipelining Overview Coding Functional Composition Q&A Session Importance of Chaining Functions Program Without Chaining Functions Demonstration 1 Output Analysis Refactoring Using Chaining Functions Demonstration 2 Output Applying Composition Using Pipelining Demonstration 3 Output Analysis Q&A Session Using HOFs Demonstration 4 Output Analysis Q&A Session Exercises Summary Solutions to Exercises E4.1 E4.2 E4.3 E4.4 E4.5 Chapter 5: Composing Functions Using Currying Overview of Currying Program Without Currying Demonstration 1 Output Analysis Using the Concept of Currying Demonstration 2 Output Analysis Q&A Session Demonstration 3 Output Using External NuGet Packages Using Curryfy Q&A Session Case Study Demonstration 4 Output Analysis Q&A Session Exercises Summary Solutions to Exercises E5.1 E5.2 E5.3 E5.4 E5.5 E5.6 Chapter 6: Handling Temporal Coupling Temporal Coupling Overview How Does This Happen? Q&A Session Recognizing the Problem A Program That Suffers from Temporal Coupling Demonstration 1 Output How Does It Cause Problems? Q&A Session Removing the Effect A Better Program Demonstration 2 Output Analysis Conclusion Q&A Session Exercises Summary Solutions to Exercises E6.1 E6.2 E6.3 E6.4 E6.5 Chapter 7: Functional Patterns Map Pattern Understanding the Problem Initial Solution Demonstration 1 Output Better Solution Concise Solution Q&A Session Select As Map Demonstration 2 Q&A Session Introducing Functors Conclusion Q&A Session Bind Pattern Understanding the Problem Initial Solution FP-Based Solution Demonstration 3 Output SelectMany As Bind Demonstration 4 What About Monads? Conclusion Q&A Session Filter Pattern Understanding the Problem Initial Solution Demonstration 5 Output Where As Filter Demonstration 6 Conclusion Fold Pattern Understanding the Problem Solutions Using Built-in Functions Demonstration 7 Output Conclusion Q&A Session Revisiting ForEach Exercises Summary Solutions to Exercises E7.1 E7.2 E7.3 E7.4 E7.5 E7.6 E7.7 E7.8 Chapter 8: Exception Handling Reviewing Exception Handling in OOP Imperative Style of Programming Demonstration 1 Output Exception Handling in FP Using language-ext Introducing the Either Type How Does It Work? Handling a Single Exception Demonstration 2 Output Q&A Session Handling Multiple Exceptions Demonstration 3 Output Analysis Q&A Session Chaining Exceptions Demonstration 4 Output Demonstration 5 Output Q&A Session Handling Null Values Introducing the Option Type How Does It Work? Q&A Session Partial Functions and Options Q&A Session Exercises Summary Solutions to Exercises E8.1 E8.2 E8.3 E8.4 Output E8.5 Output Chapter 9: Miscellaneous Topics Helpful Features for FP Delegates and Lambdas Anonymous Methods Extension Methods and LINQ Q&A Session Type Inference Importing Static Members Q&A Session Immutability Features Expression-Bodied Members Q&A Session Local Functions Q&A Session Tuples Q&A Session Pattern Matching Revisiting Option Bind Function Return Function Introducing Monads Definition Mathematical Background Monad Laws Understanding the Haskell Notations Monad Laws for C# Developers Chaining Multi-argument Functions Final Suggestions Command Query Separation Learn Design Patterns and Anti-Patterns Don’t Let Failures Stop You How Much Functional Code Do I Need? Applications of FP The Road Ahead Exercises Summary Solutions to Exercises E9.1 E9.2 E9.3 E9.4 E9.5 E9.6 E9.7 Appendix: Recommended Resources Books Documentation Courses Other Resources Index