Search icon CANCEL
Arrow left icon
Explore Products
Best Sellers
New Releases
Books
Videos
Audiobooks
Learning Hub
Conferences
Free Learning
Arrow right icon
Clojure Reactive Programming
Clojure Reactive Programming

Clojure Reactive Programming: Design and implement highly reusable reactive applications by integrating different frameworks with Clojure

Arrow left icon
Profile Icon Leonardo Borges
Arrow right icon
Free Trial
Full star icon Full star icon Full star icon Full star icon Half star icon 4.3 (13 Ratings)
Paperback Mar 2015 232 pages 1st Edition
eBook
Mex$561.99 Mex$803.99
Paperback
Mex$1004.99
Subscription
Free Trial
Arrow left icon
Profile Icon Leonardo Borges
Arrow right icon
Free Trial
Full star icon Full star icon Full star icon Full star icon Half star icon 4.3 (13 Ratings)
Paperback Mar 2015 232 pages 1st Edition
eBook
Mex$561.99 Mex$803.99
Paperback
Mex$1004.99
Subscription
Free Trial
eBook
Mex$561.99 Mex$803.99
Paperback
Mex$1004.99
Subscription
Free Trial

What do you get with a Packt Subscription?

Free for first 7 days. $19.99 p/m after that. Cancel any time!
Product feature icon Unlimited ad-free access to the largest independent learning library in tech. Access this title and thousands more!
Product feature icon 50+ new titles added per month, including many first-to-market concepts and exclusive early access to books as they are being written.
Product feature icon Innovative learning tools, including AI book assistants, code context explainers, and text-to-speech.
Product feature icon Thousands of reference materials covering every tech concept you need to stay up to date.
Subscribe now
View plans & pricing
Table of content icon View table of contents Preview book icon Preview Book

Clojure Reactive Programming

Chapter 2. A Look at Reactive Extensions

Reactive Extensions—or Rx—is a Reactive Programming library from Microsoft to build 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 the 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 the 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 sequences represent events. Rx also provides a behavior-like abstraction through another data...

The Observer pattern revisited

In Chapter 1, What is Reactive Programming?, we saw a brief overview of the Observer design pattern and a simple implementation of it in Clojure using watches. Here's how we did it:

(def numbers (atom []))

(defn adder [key ref old-state new-state]
  (print "Current sum is " (reduce + new-state)))

(add-watch numbers :adder adder) 

In the preceding example, our observable subject is the var, numbers. The observer is the adder watch. When the observable changes, it pushes its changes to the observer synchronously.

Now, contrast this to working with sequences:

(->> [1 2 3 4 5 6]
     (map inc)
     (filter even?)
     (reduce +))

This time around, the vector is the subject being observed and the functions processing it can be thought of as the observers. However, this works in a pull-based model. The vector doesn't push any elements down the sequence. Instead, map and friends ask the sequence for more elements. This is a synchronous operation...

Creating Observables

This chapter is all about Reactive Extensions, so let's go ahead and create a project called rx-playground that we will be using in our exploratory tour. We will use RxClojure (see https://github.com/ReactiveX/RxClojure), a library that provides Clojure bindings for RxJava() (see https://github.com/ReactiveX/RxJava):

$ lein new rx-playground

Open the project file and add a dependency on RxJava's Clojure bindings:

(defproject rx-playground "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.5.1"]
                 [io.reactivex/rxclojure "1.0.0"]])"]])

Now, fire up a REPL in the project's root directory so that we can start creating some observables:

$ lein repl

The first thing we need to do is import...

Manipulating Observables

Now that we know how to create observables, we should look at what kinds of interesting things we can do with them. In this section, we will see what it means to treat Observables as sequences.

We'll start with something simple. Let's print the sum of the first five positive even integers from an observable of all integers:

(rx/subscribe (->> (Observable/interval 1 TimeUnit/MICROSECONDS)
                   (rx/filter even?)
                   (rx/take 5)
                   (rx/reduce +))
                   prn-to-repl)

This is starting to look awfully familiar to us. We create an interval that will emit all positive integers starting at zero every 1 microsecond. Then, we filter all even numbers in this observable. Obviously, this is too big a list to handle, so we simply take the first five elements from it. Finally, we reduce the value using +. The result is 20.

To drive home the point that programming with observables really is just like operating...

Flatmap and friends

In the previous section, we learned how to transform and combine observables with operations such as map, reduce, and zip. However, the two observables above—musicians and bands—were perfectly capable of producing values on their own. They did not need any extra input.

In this section, we examine a different scenario: we'll learn how we can combine observables, where the output of one is the input of another. We encountered flatmap before in Chapter 1, What is Reactive Programming? If you have been wondering what its role is, this section addresses exactly that.

Here's what we are going to do: given an observable representing a list of all positive integers, we'll calculate the factorial for all even numbers in that list. Since the list is too big, we'll take five items from it. The end result should be the factorials of 0, 2, 4, 6, and 8, respectively.

The first thing we need is a function to calculate the factorial of a number n, as well...

Error handling

A very important aspect of building reliable applications is knowing what to do when things go wrong. It is naive to assume that the network is reliable, that hardware won't fail, or that we, as developers, won't make mistakes.

RxJava embraces this fact and provides a rich set of combinators to deal with failure, a few of which we examine here.

OnError

Let's get started by creating a badly behaved observable that always throws an exception:

(defn exceptional-obs []
  (rx/observable*
   (fn [observer]
     (rx/on-next observer (throw (Exception. "Oops. Something went wrong")))
     (rx/on-completed observer))))

Now let's watch what happens if we subscribe to it:

(rx/subscribe (->> (exceptional-obs)
                   (rx/map inc))
              (fn [v] (prn-to-repl "result is " v)))

;; Exception Oops. Something went wrong  rx-playground.core/exceptional-obs/fn--1505

The exception thrown by exceptional-obs isn't caught anywhere so...

The Observer pattern revisited


In Chapter 1, What is Reactive Programming?, we saw a brief overview of the Observer design pattern and a simple implementation of it in Clojure using watches. Here's how we did it:

(def numbers (atom []))

(defn adder [key ref old-state new-state]
  (print "Current sum is " (reduce + new-state)))

(add-watch numbers :adder adder) 

In the preceding example, our observable subject is the var, numbers. The observer is the adder watch. When the observable changes, it pushes its changes to the observer synchronously.

Now, contrast this to working with sequences:

(->> [1 2 3 4 5 6]
     (map inc)
     (filter even?)
     (reduce +))

This time around, the vector is the subject being observed and the functions processing it can be thought of as the observers. However, this works in a pull-based model. The vector doesn't push any elements down the sequence. Instead, map and friends ask the sequence for more elements. This is a synchronous operation.

Rx makes sequences...

Creating Observables


This chapter is all about Reactive Extensions, so let's go ahead and create a project called rx-playground that we will be using in our exploratory tour. We will use RxClojure (see https://github.com/ReactiveX/RxClojure), a library that provides Clojure bindings for RxJava() (see https://github.com/ReactiveX/RxJava):

$ lein new rx-playground

Open the project file and add a dependency on RxJava's Clojure bindings:

(defproject rx-playground "0.1.0-SNAPSHOT"
  :description "FIXME: write description"
  :url "http://example.com/FIXME"
  :license {:name "Eclipse Public License"
            :url "http://www.eclipse.org/legal/epl-v10.html"}
  :dependencies [[org.clojure/clojure "1.5.1"]
                 [io.reactivex/rxclojure "1.0.0"]])"]])

Now, fire up a REPL in the project's root directory so that we can start creating some observables:

$ lein repl

The first thing we need to do is import RxClojure, so let's get this out of the way by typing the following in the REPL:

(require...
Left arrow icon Right arrow icon
Download code icon Download Code

Description

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.

What you will learn

  • Understand the key abstractions of Functional Reactive Programming (FRP) and Compositional Event Systems (CES)
  • Discover how to think in terms of timevarying values and event streams
  • Create, compose, and transform Observable sequences with Reactive Extensions
  • Create a CES framework from scratch using core.async as its foundation
  • Build a simple ClojureScript game using Reagi
  • Integrate Om and RxJS in a web application
  • Implement a reactive API to Amazon Web Services
  • Discover approaches to backpressure and error handling
  • Get to grips with futures and learn where they fit in

Product Details

Country selected
Publication date, Length, Edition, Language, ISBN-13
Publication date : Mar 23, 2015
Length: 232 pages
Edition : 1st
Language : English
ISBN-13 : 9781783986668
Vendor :
Eclipse Foundation
Category :
Languages :

What do you get with a Packt Subscription?

Free for first 7 days. $19.99 p/m after that. Cancel any time!
Product feature icon Unlimited ad-free access to the largest independent learning library in tech. Access this title and thousands more!
Product feature icon 50+ new titles added per month, including many first-to-market concepts and exclusive early access to books as they are being written.
Product feature icon Innovative learning tools, including AI book assistants, code context explainers, and text-to-speech.
Product feature icon Thousands of reference materials covering every tech concept you need to stay up to date.
Subscribe now
View plans & pricing

Product Details

Publication date : Mar 23, 2015
Length: 232 pages
Edition : 1st
Language : English
ISBN-13 : 9781783986668
Vendor :
Eclipse Foundation
Category :
Languages :

Packt Subscriptions

See our plans and pricing
Modal Close icon
$19.99 billed monthly
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Simple pricing, no contract
$199.99 billed annually
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just Mex$85 each
Feature tick icon Exclusive print discounts
$279.99 billed in 18 months
Feature tick icon Unlimited access to Packt's library of 7,000+ practical books and videos
Feature tick icon Constantly refreshed with 50+ new titles a month
Feature tick icon Exclusive Early access to books as they're written
Feature tick icon Solve problems while you work with advanced search and reference features
Feature tick icon Offline reading on the mobile app
Feature tick icon Choose a DRM-free eBook or Video every month to keep
Feature tick icon PLUS own as many other DRM-free eBooks or Videos as you like for just Mex$85 each
Feature tick icon Exclusive print discounts

Frequently bought together


Stars icon
Total Mex$ 3,014.97
Scala for Java Developers
Mex$1004.99
Clojure Reactive Programming
Mex$1004.99
Learning Reactive Programming With Java 8
Mex$1004.99
Total Mex$ 3,014.97 Stars icon

Table of Contents

12 Chapters
1. What is Reactive Programming? Chevron down icon Chevron up icon
2. A Look at Reactive Extensions Chevron down icon Chevron up icon
3. Asynchronous Programming and Networking Chevron down icon Chevron up icon
4. Introduction to core.async Chevron down icon Chevron up icon
5. Creating Your Own CES Framework with core.async Chevron down icon Chevron up icon
6. Building a Simple ClojureScript Game with Reagi Chevron down icon Chevron up icon
7. The UI as a Function Chevron down icon Chevron up icon
8. Futures Chevron down icon Chevron up icon
9. A Reactive API to Amazon Web Services Chevron down icon Chevron up icon
A. The Algebra of Library Design Chevron down icon Chevron up icon
B. Bibliography Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Top Reviews
Rating distribution
Full star icon Full star icon Full star icon Full star icon Half star icon 4.3
(13 Ratings)
5 star 76.9%
4 star 0%
3 star 7.7%
2 star 7.7%
1 star 7.7%
Filter icon Filter
Top Reviews

Filter reviews by




Lucas Medeiros Reis Aug 31, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This is an intermediate to advanced book on Clojure and Clojurescript programming. It's a selection of techniques for concurrency, asynchronous and reactive programming, with a perfect balance of practice and theory.Chapter 4, on core async, is a good example is chapter 4. Borges outlines the issues with using callbacks to deal with concurrency, and he also discusses Communicating Sequential Processes as a solution. That's the theory. Then, he shows an implementation of this solution using Futures, and also explains the core async library. The rest of the chapter is an implementation of a toy stock market app. This to be the best material on learning core async that I've found.The other chapters are just as good. Don't miss it if you are interested in taking your Clojure skills to the next level.
Amazon Verified review Amazon
Claudio Natoli Jul 08, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I was fortunate to have seen a small part of this title ahead of print; consequently, I had high hopes for the full published work, and was not disappointed.This title is a solid compendium of FRP in Clojure. After a brief introduction to the history, terms and patterns of FRP, you'll find yourself reading about such topics as Rx, asynchronous networking, core.async, Om, futures and more, with numerous examples covering at times both Clojure and ClojureScript.On the topic of examples, one highlight of this book is the frequent revisiting of a particular problem or snippet, with alternative approaches, as motivating examples for how Reactive Programming and/or different libraries and patterns can be leveraged. For instance, the Futures chapter develops an example using clojure.core futures, and then illustrates some of the difficulties in their application by constrasting with an alternative library developed by the author.While a broad range of concepts are covered, the material should be accessible even to those relatively new to Clojure (if you know what "lein" is, you're good to go!)
Amazon Verified review Amazon
neuronsong Nov 19, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
I would gladly buy from this seller again.
Amazon Verified review Amazon
Amazon Customer May 31, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
This short, focused book nicely covers both the concepts and clojure/clojurescript applications of Reactive programming (FRP). Reading it will give you a nice, efficient push up the learning curve. There's no better praise for a technical book, in my view.
Amazon Verified review Amazon
Amazon Customer Apr 08, 2015
Full star icon Full star icon Full star icon Full star icon Full star icon 5
Amazing book, I highly recommend it!
Amazon Verified review Amazon
Get free access to Packt library with over 7500+ books and video courses for 7 days!
Start Free Trial

FAQs

What is included in a Packt subscription? Chevron down icon Chevron up icon

A subscription provides you with full access to view all Packt and licnesed content online, this includes exclusive access to Early Access titles. Depending on the tier chosen you can also earn credits and discounts to use for owning content

How can I cancel my subscription? Chevron down icon Chevron up icon

To cancel your subscription with us simply go to the account page - found in the top right of the page or at https://subscription.packtpub.com/my-account/subscription - From here you will see the ‘cancel subscription’ button in the grey box with your subscription information in.

What are credits? Chevron down icon Chevron up icon

Credits can be earned from reading 40 section of any title within the payment cycle - a month starting from the day of subscription payment. You also earn a Credit every month if you subscribe to our annual or 18 month plans. Credits can be used to buy books DRM free, the same way that you would pay for a book. Your credits can be found in the subscription homepage - subscription.packtpub.com - clicking on ‘the my’ library dropdown and selecting ‘credits’.

What happens if an Early Access Course is cancelled? Chevron down icon Chevron up icon

Projects are rarely cancelled, but sometimes it's unavoidable. If an Early Access course is cancelled or excessively delayed, you can exchange your purchase for another course. For further details, please contact us here.

Where can I send feedback about an Early Access title? Chevron down icon Chevron up icon

If you have any feedback about the product you're reading, or Early Access in general, then please fill out a contact form here and we'll make sure the feedback gets to the right team. 

Can I download the code files for Early Access titles? Chevron down icon Chevron up icon

We try to ensure that all books in Early Access have code available to use, download, and fork on GitHub. This helps us be more agile in the development of the book, and helps keep the often changing code base of new versions and new technologies as up to date as possible. Unfortunately, however, there will be rare cases when it is not possible for us to have downloadable code samples available until publication.

When we publish the book, the code files will also be available to download from the Packt website.

How accurate is the publication date? Chevron down icon Chevron up icon

The publication date is as accurate as we can be at any point in the project. Unfortunately, delays can happen. Often those delays are out of our control, such as changes to the technology code base or delays in the tech release. We do our best to give you an accurate estimate of the publication date at any given time, and as more chapters are delivered, the more accurate the delivery date will become.

How will I know when new chapters are ready? Chevron down icon Chevron up icon

We'll let you know every time there has been an update to a course that you've bought in Early Access. You'll get an email to let you know there has been a new chapter, or a change to a previous chapter. The new chapters are automatically added to your account, so you can also check back there any time you're ready and download or read them online.

I am a Packt subscriber, do I get Early Access? Chevron down icon Chevron up icon

Yes, all Early Access content is fully available through your subscription. You will need to have a paid for or active trial subscription in order to access all titles.

How is Early Access delivered? Chevron down icon Chevron up icon

Early Access is currently only available as a PDF or through our online reader. As we make changes or add new chapters, the files in your Packt account will be updated so you can download them again or view them online immediately.

How do I buy Early Access content? Chevron down icon Chevron up icon

Early Access is a way of us getting our content to you quicker, but the method of buying the Early Access course is still the same. Just find the course you want to buy, go through the check-out steps, and you’ll get a confirmation email from us with information and a link to the relevant Early Access courses.

What is Early Access? Chevron down icon Chevron up icon

Keeping up to date with the latest technology is difficult; new versions, new frameworks, new techniques. This feature gives you a head-start to our content, as it's being created. With Early Access you'll receive each chapter as it's written, and get regular updates throughout the product's development, as well as the final course as soon as it's ready.We created Early Access as a means of giving you the information you need, as soon as it's available. As we go through the process of developing a course, 99% of it can be ready but we can't publish until that last 1% falls in to place. Early Access helps to unlock the potential of our content early, to help you start your learning when you need it most. You not only get access to every chapter as it's delivered, edited, and updated, but you'll also get the finalized, DRM-free product to download in any format you want when it's published. As a member of Packt, you'll also be eligible for our exclusive offers, including a free course every day, and discounts on new and popular titles.