Book Image

Hands-On Reactive Programming with Clojure - Second Edition

By : Konrad Szydlo, Leonardo Borges
Book Image

Hands-On Reactive Programming with Clojure - Second Edition

By: Konrad Szydlo, Leonardo Borges

Overview of this book

Reactive Programming is central to many concurrent systems, and can help make the process of developing highly concurrent, event-driven, and asynchronous applications simpler and less error-prone. This book will allow you to explore Reactive Programming in Clojure 1.9 and help you get to grips with some of its new features such as transducers, reader conditionals, additional string functions, direct linking, and socket servers. Hands-On Reactive Programming with Clojure starts by introducing you to Functional Reactive Programming (FRP) and its formulations, as well as showing you how it inspired Compositional Event Systems (CES). It then guides you in understanding Reactive Programming as well as learning how to develop your ability to work with time-varying values thanks to examples of reactive applications implemented in different frameworks. You'll also gain insight into some interesting Reactive design patterns such as the simple component, circuit breaker, request-response, and multiple-master replication. Finally, the book introduces microservices-based architecture in Clojure and closes with examples of unit testing frameworks. By the end of the book, you will have gained all the knowledge you need to create applications using different Reactive Programming approaches.

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Table of Contents (15 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Get in touch
Free Chapter
1
What is Reactive Programming?
What is Reactive Programming?
A taste of Reactive Programming
A bit of history
Signals and events
Implementation challenges
Applications of FRP
Summary
Further reading
2
A Look at Reactive Extensions
A Look at Reactive Extensions
The observer pattern revisited
Creating observables
Manipulating observables
flatmap and friends
Error handling
Backpressure
Summary
Further reading
3
Asynchronous Programming and Networking
Asynchronous Programming and Networking
Building a stock market monitoring application
Rolling averages
Identifying problems with our current approach
Removing incidental complexity with RxClojure
Summary
4
Introduction to core.async
Introduction to core.async
Asynchronous programming and concurrency
The core.async library
Rewriting the stock market application with core.async
Error handling
Backpressure
Transducers
Summary
Further reading
5
Creating Your Own CES Framework with core.async
Creating Your Own CES Framework with core.async
A minimal CES framework
Exercises
A respondent application
CES versus core.async
Summary
Further reading
6
Building a Simple ClojureScript Game with Reagi
Building a Simple ClojureScript Game with Reagi
Setting up the project
Reagi and other CES frameworks
Summary
Further reading
7
The UI as a Function
The UI as a Function
The problem with complex web UIs
Enter React.js
ClojureScript and Om
Building a simple Contacts application with Om
Intercomponent communication
Exercises
Summary
Further reading
8
A New Approach to Futures
A New Approach to Futures
Clojure futures
Fetching data in parallel
Imminent – a composable futures library for Clojure
The movies example revisited
Futures and blocking IO
Summary
Further reading
9
A Reactive API to Amazon Web Services
A Reactive API to Amazon Web Services
Amazon Services use case
Infrastructure automation
AWS resources dashboard
CloudFormation
Elastic Compute Cloud Service
Relational Database Service
Designing the solution
Exercises
Summary
Further reading
10
Reactive Microservices
Reactive Microservices
An introduction to microservices
Microservices best practices
Communication between services
Common pitfalls
RESTful microservices in action
Summary
Further reading
11
Testing Reactive Apps
Testing Reactive Apps
Why testing is important
Testing approaches
Clojure unit testing frameworks
Summary
Further reading
12
Concurrency Utilities in Clojure
Concurrency Utilities in Clojure
Introduction to concurrency
State, identity, and value
The Clojure approach to concurrency
Futures and promises in Clojure
Summary
Further reading
13
Other Books You May Enjoy
Other Books You May Enjoy
Leave a review - let other readers know what you think
Appendix - The Algebra of Library Design
Appendix - The Algebra of Library Design
The semantics of map
Finding the average of ages
Applicative functors
Gathering stats about ages
Monads
Summary
Further reading

A Look at Reactive Extensions

Reactive Extensions (Rx) is a Reactive Programming library from Microsoft that's used for building complex asynchronous programs. It models time-varying values and events as observable sequences and is implemented by extending the Observer design pattern.

Its first target platform was .NET, but Netflix has ported Rx to JVM under the name RxJava. Microsoft also develops and maintains a port of Rx to JavaScript called RxJS, which is the tool we used to build the sine wave application. The two ports work a treat for us, since Clojure runs on JVM and ClojureScript in JavaScript environments.

As we saw in Chapter 1, What is Reactive Programming?, Rx is inspired by Functional Reactive Programming but uses different terminology. In FRP, the two main abstractions are behaviors and events. Although the implementation details are different, observable...

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