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Clojure Reactive Programming

By : Leonardo Borges

4.3 (13)

Clojure Reactive Programming

4.3 (13)

By: Leonardo Borges

Overview of this book

If you are a Clojure developer who is interested in using Reactive Programming to build asynchronous and concurrent applications, this book is for you. Knowledge of Clojure and Leiningen is required. Basic understanding of ClojureScript will be helpful for the web chapters, although it is not strictly necessary.

Preface

Preface

What this book covers

What you need for this book

Who this book is for

Conventions

Reader feedback

Customer support

Free Chapter

1. What is Reactive Programming?

1. What is Reactive Programming?

A taste of Reactive Programming

A bit of history

Signals and events

Implementation challenges

Applications of FRP

Summary

2. A Look at Reactive Extensions

2. A Look at Reactive Extensions

The Observer pattern revisited

Creating Observables

Manipulating Observables

Flatmap and friends

Error handling

Backpressure

Summary

3. Asynchronous Programming and Networking

3. 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

4. Introduction to core.async

Asynchronous programming and concurrency

core.async

Rewriting the stock market application with core.async

Error handling

Backpressure

Transducers

Summary

5. Creating Your Own CES Framework with core.async

5. Creating Your Own CES Framework with core.async

A minimal CES framework

Exercises

A respondent application

CES versus core.async

Summary

6. Building a Simple ClojureScript Game with Reagi

6. Building a Simple ClojureScript Game with Reagi

Setting up the project

Reagi and other CES frameworks

Summary

7. The UI as a Function

7. 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

8. Futures

8. Futures

Clojure futures

Fetching data in parallel

Imminent – a composable futures library for Clojure

The movies example revisited

Futures and blocking IO

Summary

9. A Reactive API to Amazon Web Services

9. A Reactive API to Amazon Web Services

The problem

Infrastructure automation

AWS resources dashboard

CloudFormation

EC2

RDS

Designing the solution

Exercises

Summary

A. The Algebra of Library Design

A. The Algebra of Library Design

The semantics of map

Finding the average of ages

Applicative Functors

Gathering stats about ages

Monads

Summary

B. Bibliography

B. Bibliography

Index

Index

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Error handling

Back in Chapter 2, A Look at Reactive Extensions, we learned how Reactive Extensions treats errors and exceptions. It provides a rich set of combinators to deal with exceptional cases and are straightforward to use.

Despite being a pleasure to work with, core.async doesn't ship with much support for exception handling. In fact, if we write our code with only the happy path in mind we don't even know an error occurred!

Let's have a look at an example:

(defn get-data []
  (throw (Exception. "Bad things happen!")))

(defn process []
  (let [result (chan)]
    ;; do some processing...
    (go (>! result (get-data)))
    result))

In the preceding snippet, we introduced two functions:

get-data simulates a function that fetches data from the network or an in-memory cache. In this case it simply throws an exception.
process is a function that depends on get-data to do something interesting and puts the result into a channel, which is returned at the end.

Let's watch what happens when...

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