Clojure Reactive Programming

Leonardo Borges

• Publisher: Packt Publishing
• Year: 2015
• eBook ISBN: 9781783986668
• Topic: Computer Science
• Subtopic: Programming in JavaScript
• Index: Computer Science

Clojure Reactive Programming

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Table of Contents

Clojure Reactive Programming

Credits

About the Author

Acknowledgments

About the Reviewers

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Free access for Packt account holders

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Downloading the example code

Errata

Piracy

Questions

1. What is Reactive Programming?

A taste of Reactive Programming

Creating time

More colors

Making it reactive

Exercise 1.1

A bit of history

Dataflow programming

Object-oriented Reactive Programming

The most widely used reactive program

The Observer design pattern

Functional Reactive Programming

Higher-order FRP

Signals and events

Implementation challenges

First-order FRP

Asynchronous data flow

Arrowized FRP

Applications of FRP

Asynchronous programming and networking

Complex GUIs and animations

Summary

2. A Look at Reactive Extensions

The Observer pattern revisited

Observer – an Iterator's dual

Creating Observables

Custom Observables

Manipulating Observables

Flatmap and friends

One more flatmap for the road

Error handling

OnError

Catch

Retry

Backpressure

Sample

Backpressure strategies

Summary

3. Asynchronous Programming and Networking

Building a stock market monitoring application

Rolling averages

Identifying problems with our current approach

Removing incidental complexity with RxClojure

Observable rolling averages

Summary

4. Introduction to core.async

Asynchronous programming and concurrency

core.async

Communicating sequential processes

Rewriting the stock market application with core.async

Implementing the application code

Error handling

Backpressure

Fixed buffer

Dropping buffer

Sliding buffer

Transducers

Transducers and core.async

Summary

5. Creating Your Own CES Framework with core.async

A minimal CES framework

Clojure or ClojureScript?

Designing the public API

Implementing tokens

Implementing event streams

Implementing behaviors

Exercises

Exercise 5.1

Exercise 5.2

A respondent application

CES versus core.async

Summary

6. Building a Simple ClojureScript Game with Reagi

Setting up the project

Game entities

Putting it all together

Modeling user input as event streams

Working with the active keys stream

Reagi and other CES frameworks

Summary

7. The UI as a Function

The problem with complex web UIs

Enter React.js

Lessons from functional programming

ClojureScript and Om

Building a simple Contacts application with Om

The Contacts application state

Setting up the Contacts project

Application components

Om cursors

Filling in the blanks

Intercomponent communication

Creating an agile board with Om

The board state

Components overview

Lifecycle and component local state

Remaining components

Utility functions

Exercises

Summary

8. Futures

Clojure futures

Fetching data in parallel

Imminent – a composable futures library for Clojure

Creating futures

Combinators and event handlers

The movies example revisited

Futures and blocking IO

Summary

9. A Reactive API to Amazon Web Services

The problem

Infrastructure automation

AWS resources dashboard

CloudFormation

The describeStacks endpoint

The describeStackResources endpoint

EC2

The describeInstances endpoint

RDS

The describeDBInstances endpoint

Designing the solution

Running the AWS stub server

Setting up the dashboard project

Creating AWS Observables

Combining the AWS Observables

Putting it all together

Exercises

Summary

A. The Algebra of Library Design

The semantics of map

Functors

The Option Functor

Finding the average of ages

Applicative Functors

Gathering stats about ages

Monads

Summary

B. Bibliography

Index

Clojure Reactive Programming

Copyright © 2015 Packt Publishing

All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews.

Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book.

Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information.

First published: March 2015

Production reference: 1160315

Published by Packt Publishing Ltd.

Livery Place

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Birmingham B3 2PB, UK.

ISBN 978-1-78398-666-8

www.packtpub.com

Credits

Author

Leonardo Borges

Reviewers

Eduard Bondarenko

Colin Jones

Michael Kohl

Falko Riemenschneider

Acquisition Editor

Harsha Bharwani

Content Development Editor

Arun Nadar

Technical Editor

Tanvi Bhatt

Copy Editors

Vikrant Phadke

Sameen Siddiqui

Project Coordinator

Neha Bhatnagar

Proofreaders

Simran Bhogal

Maria Gould

Indexer

Mariammal Chettiyar

Graphics

Abhinash Sahu

Production Coordinator

Manu Joseph

Cover Work

Manu Joseph

About the Author

Leonardo Borges is a programming languages enthusiast who loves writing code, contributing to open source software, and speaking on subjects he feels strongly about. After nearly 5 years of consulting at ThoughtWorks, where he worked in two commercial Clojure projects, among many others, he is now a software engineer at Atlassian. He uses Clojure and ClojureScript to help build real-time collaborative editing technology. This is his first full-length book, but he contributed a couple of chapters to Clojure Cookbook, O'Reilly.

Leonardo has founded and runs the Sydney Clojure User Group in Australia. He also writes posts about software, focusing on functional programming, on his website (http://www.leonardoborges.com). When he isn't writing code, he enjoys riding motorcycles, weightlifting, and playing the guitar.

Acknowledgments

I would like to take this opportunity and start by thanking my family: my grandparents, Altamir and Alba, for their tireless support; my mother, Sônia, for her unconditional love and motivation; and my uncle, Altamir Filho, for supporting me when I decided to go to school at night so that I could start working as a programmer. Without them, I would have never pursued software engineering.

I would also like to thank my fiancee, Enif, who answered with a resounding "yes" when asked whether I should take up the challenge of writing a...

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