Functional Programming in C# (.NET)

The book "Functional Programming in C# (.NET)" is a comprehensive guide for developers seeking to master the functional coding style within the .NET ecosystem. The author, Alexey Vorontsov, an experienced architect and C# practitioner, consistently guides the reader from basic concepts to advanced techniques, demonstrating how functional programming makes code more predictable, testable, and resilient to errors.

What is this book about?

The book covers all key aspects of functional programming in the context of C#:

• Paradigm fundamentals: pure functions, data immutability, absence of side effects.
• Working with LINQ and lambda expressions: declarative collection processing, query composition.
• Higher-order functions: using Func/Action delegates, currying, and partial application.
• Monads and functors: implementing Maybe (Option), Either, State in C# for safe error and state handling.
• Design patterns: composition, decorator, chain of responsibility in a functional style.
• Asynchrony and parallelism: using Task, Reactive Extensions (Rx.NET), and Dataflow channels.
• Integration with F#: how to leverage the power of F# in C# projects without rewriting all the code.

Who is this book for?

The book will be useful for:

• C# developers who want to write more concise and reliable code.
• .NET application architects seeking to reduce complexity and the number of errors.
• Programmers familiar with OOP but wishing to expand their toolkit with functional approaches.
• Those transitioning from other languages (Java, Python, JavaScript) to C# and wanting to apply their functional experience.

What will the reader learn?

• How to replace mutable objects with immutable data structures.
• How to use LINQ not only for basic queries but also for complex transformations.
• How to avoid exceptions using monadic types.
• How to design an architecture resilient to change using function composition.
• How to effectively use asynchronous streams and reactive sequences.
• How to combine functional and object-oriented styles in a single project.

All code examples are accompanied by detailed comments and can be run on .NET 8+. The book contains practical exercises and real-world cases from industrial development. This is not just theory — it is ready-to-apply techniques that will improve the quality of your code today.