Domain Modeling Made Functional

You want increased customer satisfaction, faster development cycles, and less wasted work. Domain-driven design (DDD) combined with functional programming is the innovative combo that will get you there. In this pragmatic, down-to-earth guide, you’ll see how applying the core principles of functional programming can result in software designs that model real-world requirements both elegantly and concisely – often more so than an object-oriented approach. Practical examples in the open-source F# functional language, and examples from familiar business domains, show you how to apply these techniques to build software that is business-focused, flexible, and high quality.

Domain-driven design is a well-established approach to designing software that ensures that domain experts and developers work together effectively to create high-quality software. This book is the first to combine DDD with techniques from statically typed functional programming. This book is perfect for newcomers to DDD or functional programming – all the techniques you need will be introduced and explained.

Model a complex domain accurately using the F# type system, creating compilable code that is also readable documentation—ensuring that the code and design never get out of sync. Encode business rules in the design so that you have “compile-time unit tests,” and eliminate many potential bugs by making illegal states unrepresentable. Assemble a series of small, testable functions into a complete use case, and compose these individual scenarios into a large-scale design. Discover why the combination of functional programming and DDD leads naturally to service-oriented and hexagonal architectures. Finally, create a functional domain model that works with traditional databases, NoSQL, and event stores, and safely expose your domain via a website or API.

Solve real problems by focusing on real-world requirements for your software.

What You Need:

The code in this book is designed to be run interactively on Windows, Mac and Linux. You will need a recent version of F# (4.0 or greater), and the appropriate .NET runtime for your platform. Full installation instructions for all platforms at fsharp.org.

Table of Contents

Part I — Understanding the Domain

1. Introducing Domain-Driven Design

2. Understanding the Domain

3. A Functional Architecture

Part II — Modeling the Domain

4. Understanding Types

5. Domain Modeling with Types

6. Integrity and Consistency in the Domain

7. Modeling Workflows as Pipelines

Part III — Implementing the Model

8. Understanding Functions

9. Implementation: Composing a Pipeline

10. Implementation: Working with Errors

11. Serialization

12. Persistence

13. Evolving a Design and Keeping It Clean

About the Author

Scott Wlaschin is an expert on F#, author of the popular F# site fsharpforfunandprofit.com, and a board member of the F# Software Foundation. Known for his non-academic approach to functional programming, Scott is a popular speaker and has given talks at NDC, F# Exchange, DDD Europe, and other conferences around the world.