Functional Design and Architecture (Early Edition, 2020) (E-Book (First Edition) + Code Samples)
Functional Design and Architecture (Early Edition, 2020)
Building real programs in static functional languages: application architectures, design patterns, best practices and approaches
About the Book
Important: this is the Early Edition of the book self-published in 2020.
* Consider buying Functional Design and Architecture, significantly reworked and published by Manning in 2024.
* See also my new book Pragmatic Type-Level Design.
FDaA is a fundamental book about Software Design in Haskell and other functional languages. The main idea of this book is to provide a comprehensive source of knowledge, and a complete methodology for building real-world applications. Application architectures, best practices, design patterns, and approaches, - all the information you need to achieve a simple, maintainable, testable code with low complexity and low risks. By reading this book, you’ll learn many useful techniques: from the requirement analysis to the implementation of particular subsystems such as SQL and NoSQL databases, multithreading, and logging. You’ll learn about design principles, application layers, functional interfaces, Inversion of Control, and Dependency Injection.
The book has 9 chapters, 780K symbols, 120K words.
The book is very practical. It will be useful for software engineers who want to improve their software design skills with a strong relation to many advanced Haskell concepts.
The book requires a certain level of Haskell knowledge, up to intermediate.
The book covers a big gap in the Haskell ecosystem: the lack of resources for high-level application design. It’s also important that the ideas from the book were used in real production with great success. The book offers my own methodology - Functional Declarative Design, with Hierarchical Free Monads as a core technology. Using this methodology, I created several real-world frameworks, and they are driving a successful business in several companies.
There is a limited colored hardcover version of the book of the highest printing quality. This is what it looks like (video). Shipping is not possible at the moment.
Book topics:
- requirements analysis and architecture modeling;
- application layering;
- design principles, SOLID;
- Haskell-specific design patterns;
- Inversion of Control and Dependency Injection;
- domain modeling, embedded and external DSLs;
- functional interfaces, subsystems, and services;
- Free monads, ReaderT pattern, Service handle pattern;
- Final Tagless/mtl, GADTs
- multithreading and concurrency;
- state and stateful applications;
- design of business logic;
- interaction with impure subsystems;
- relational and key-value databases;
- error handling, exceptions, error domains;
- web servers, HTTP backends, CLI applications;
- property-based, functional, and integration testing;
- black box and white box testing.
The book is project-based. There are two showcase projects for it:
- Hydra, a full-fledged framework for building web services, multithreaded, and concurrent applications with SQL and KV DB support. Contains 3 engines: Final Tagless, Free Monad, and Church Encoded Free Monad, as well as several demo applications to compare these 3 approaches.
- Andromeda, a SCADA software for spaceship control.
I designed the following real-world frameworks using the ideas from the book (with the help of other people of course):
- EulerHS - a Haskell framework for web backends and console apps. Has many subsystems out of the box: SQL DBs support (Postgres, MySQL, SQLite), KV DBs support (Reddis), logging, concurrent flows, exception handling, automatic whitebox testing, typed options and other stuff.
- PureScript Presto - a PureScript framework for building mobile apps using a handy eDSL.
- PureScript Presto.Backend - a PureScript framework for web backends. It has the same design as Presto but also is empowered by some additional features like logging, HTTP APIs integration, KV DB, SQL DB subsystems, state handling, automatic whitebox testing, and other useful stuff.
All of these frameworks drive the business of an Indian financial company Juspay. Its mobile apps and financial backends have hundreds of thousands of lines of code, and these frameworks are really tested in production. This technology helped the company to grow and enabled wide adoption of PureScript and Haskell. Essentially, Juspay was the first company I used my ideas. We found that Hierarchical Free Monads hide all the complexity of implementation details behind convenient interfaces so that the code is understandable by not only developers but by managers as well. This helped us to easily reason about the domain, the logic, the business goals and the requirements. My approach also brought confidence that Haskell and PureScript are not only academic languages.
- Node - a full-fledged framework for building distributed, concurrent, multithreading apps, and blockchains initially, but not only. I designed this framework for Enecuum and then we successfully created our own blockchain using it. What's important, we managed to achieve our goals less than in 4 months with a team of 4 haskellers. The framework allowed us to write fast, complicated blockchain logic easily, quickly, without bugs and with maximum confidence due to the great testability of the HFM approach. You can read more about the framework in this my article: Building network actors with Node Framework.
About the Author
Table of Contents
- Part I Introduction to Functional Declarative Design
- 1 What is software design?
- 1.1 Software design
- 1.1.1 Requirements, goals, and simplicity
- 1.1.2 Defining software design
- 1.1.3 Low coupling, high cohesion
- 1.1.4 Interfaces, Inversion of Control and Modularity
- 1.2 Imperative design
- 1.3 Object-oriented design
- 1.3.1 Object-oriented design patterns
- 1.3.2 Object-oriented design principles
- 1.3.3 Shifting to functional programming
- 1.4 Functional declarative design
- 1.4.1 Immutability, purity and determinism in FDD
- 1.4.2 Strong static type systems in FDD
- 1.4.3 Functional patterns, idioms and thinking
- 1.5 Summary
- 1.1 Software design
- 2 Application architecture
- 2.1 Defining software architecture
- 2.1.1 Software architecture in FDD
- 2.1.2 Top-down development process
- 2.1.3 Collecting requirements
- 2.1.4 Requirements in mind maps
- 2.2 Architecture layering and modularization
- 2.2.1 Architecture layers
- 2.2.2 Modularization of applications
- 2.3 Modeling the architecture
- 2.3.1 Defining architecture components
- 2.3.2 Defining modules, subsystems and relations
- 2.3.3 Defining architecture
- 2.4 Summary
- 2.1 Defining software architecture
- 1 What is software design?
- Part II Domain Driven Design
- 3 Subsystems and services
- 3.1 Functional subsystems
- 3.1.1 Modules and libraries
- 3.1.2 Monads as subsystems
- 3.1.3 Layering subsystems with the monad stack
- 3.2 Designing the Hardware subsystem
- 3.2.1 Requirements
- 3.2.2 Algebraic data type interface to HDL
- 3.2.3 Functional interface to the Hardware subsystem
- 3.2.4 Free monad interface to HDL
- 3.2.5 Interpreter for monadic HDL
- 3.2.6 Advantages and disadvantages of a free language
- 3.3 Functional services
- 3.3.1 Pure service
- 3.3.2 Impure service
- 3.3.3 The MVar request-response pattern
- 3.3.4 Remote impure service
- 3.4 Summary
- 3.1 Functional subsystems
- 4 Domain model design
- 4.1 Defining the domain model and requirements
- 4.2 Simple embedded DSLs
- 4.2.1 Domain model eDSL using functions and primitive types
- 4.2.2 Domain model eDSL using ADT
- 4.3 Combinatorial eDSLs
- 4.3.1 Mnemonic domain analysis
- 4.3.2 Monadic Free eDSL
- 4.3.3 The abstract interpreter pattern
- 4.3.4 Free language of Free languages
- 4.3.5 Arrows for eDSLs
- 4.3.6 Arrowized eDSL over Free eDSLs
- 4.4 External DSL
- 4.4.1 External DSL structure
- 4.4.2 Parsing to the abstract syntax tree
- 4.4.3 The translation subsystem
- 4.5 Summary
- 5 Application state
- 5.1 Stateful application architecture
- 5.1.1 State in functional programming
- 5.1.2 Minimum viable product
- 5.1.3 Hardware network description language
- 5.1.4 Architecture of the simulator
- 5.2 Pure state
- 5.2.1 Argument-passing state
- 5.2.2 The State monad
- 5.3 Impure state
- 5.3.1 Impure state with IORef
- 5.3.2 Impure state with State and IO monads
- 5.4 Summary
- 5.1 Stateful application architecture
- 3 Subsystems and services
- Part III Designing real world software
- 6 Multithreading and Concurrency
- 6.1 Multithreaded applications
- 6.1.1 Why is multithreading hard?
- 6.1.2 Bare threads
- 6.1.3 Separating and abstracting the threads
- 6.1.4 Threads bookkeeping
- 6.2 Software Transactional Memory
- 6.2.1 Why STM is important
- 6.2.2 Reducing complexity with STM
- 6.2.3 Abstracting over STM
- 6.3 Useful patterns
- 6.3.1 Logging and STM
- 6.3.2 Reactive programming with processes
- 6.4 Summary
- 6.1 Multithreaded applications
- 7 Persistence
- 7.1 Database model design
- 7.1.1 Domain model and database model
- 7.1.2 Designing database model ADTs
- 7.1.3 Primary keys and the HKD pattern
- 7.1.4 Polymorphic ADTs with the HKD pattern
- 7.2 SQL and NoSQL database support
- 7.2.1 Designing untyped key-value database subsystem
- 7.2.2 Abstracted logic vs bare IO logic
- 7.2.3 Designing a SQL database model
- 7.2.4 Designing a SQL database subsystem
- 7.3 Advanced database design
- 7.3.1 Advanced SQL database subsystem
- 7.3.2 Typed key-value database model
- 7.3.3 Pools and transactions
- 7.4 Summary
- 7.1 Database model design
- 8 Business logic design
- 8.1 Business logic layering
- 8.1.1 Explicit and implicit business logic
- 8.2 Exceptions and error handling
- 8.2.1 Error domains
- 8.2.2 Native exceptions handling schemes
- 8.2.3 Free monad languages and exceptions
- 8.3 A CLI tool for reporting astronomical objects
- 8.3.1 API types and command-line interaction
- 8.3.2 HTTP and TCP client functionality
- 8.4 Functional interfaces and Dependency Injection
- 8.4.1 Service Handle Pattern
- 8.4.2 ReaderT Pattern
- 8.4.3 Additional Free monad language
- 8.4.4 GADT
- 8.4.5 Final Tagless/mtl
- 8.5 Designing web services
- 8.5.1 REST API and API types
- 8.5.2 Using the framework for business logic
- 8.5.3 Web server with Servant
- 8.5.4 Validation
- 8.5.6 Configuration management
- 8.6 Summary
- 8.1 Business logic layering
- 9 Testing
- 9.1 Testing in functional programming
- 9.1.1 Test-driven-development in functional programming
- 9.1.2 Testing basics
- 9.1.3 Property-based testing
- 9.1.4 Property-based testing of a Free monadic scenario
- 9.1.5 Integration testing
- 9.1.6 Acceptance testing
- 9.2 Advanced testing techniques
- 9.2.1 Testable architecture
- 9.2.2 Mocking with Free monads
- 9.2.3 White box unit testing
- 9.2.4 Testing framework
- 9.2.5 Automatic white box testing
- 9.3 Testability of different approaches
- 9.4 Summary
- 9.1 Testing in functional programming
- 6 Multithreading and Concurrency
- Appendix
- Appendix A Word statistics example with monad transformers
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