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Clojure Programming Cookbook

Clojure Programming Cookbook

By : Makoto Hashimoto, Modrzyk
3 (1)
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Clojure Programming Cookbook

Clojure Programming Cookbook

3 (1)
By: Makoto Hashimoto, Modrzyk

Overview of this book

When it comes to learning and using a new language you need an effective guide to be by your side when things get rough. For Clojure developers, these recipes have everything you need to take on everything this language offers. This book is divided into three high impact sections. The first section gives you an introduction to live programming and best practices. We show you how to interact with your connections by manipulating, transforming, and merging collections. You’ll learn how to work with macros, protocols, multi-methods, and transducers. We’ll also teach you how to work with languages such as Java, and Scala. The next section deals with intermediate-level content and enhances your Clojure skills, here we’ll teach you concurrency programming with Clojure for high performance. We will provide you with advanced best practices, tips on Clojure programming, and show you how to work with Clojure while developing applications. In the final section you will learn how to test, deploy and analyze websocket behavior when your app is deployed in the cloud. Finally, we will take you through DevOps. Developing with Clojure has never been easier with these recipes by your side!
Table of Contents (11 chapters)
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Preface
Preface
What this book covers
What you need for this book
Who this book is for
Sections
Conventions
Reader feedback
Customer support
Free Chapter
1
1. Live Programming with Clojure
1. Live Programming with Clojure
Introduction
REPL up!
Working with primitive data types
Using bindings of vars, conditions, loops, and error handling
Using and defining functions
Using third-party libraries
Using namespaces
What's next?
2
2. Interacting with Collections
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2. Interacting with Collections
Introduction
Clojure collections and their basic functions
Accessing and updating elements from collections
Filtering elements from collections
Transforming and sorting collections
Merging and splitting collections
How to become lazy
3
3. Clojure Next
3. Clojure Next
Introduction
Using destructuring techniques
Using functional programming style
Using threading macros
Defining simple macros
Defining more advanced macros
Using protocols
Defining multimethods
Transducers for dummies
Logic programming in Clojure
4
4. File Access and the Network
4. File Access and the Network
Introduction
Manipulating files and directories
Manipulating various formats of files - XML, JSON, YAML, and EDN
Making use of Clojure HTTP client
Using queues and topics in the RabbitMQ
Using Kafka
Using MQTT
Streaming access to provide high performance
Using Apache Camel to connect everything
5
5. Working with Other Languages
5. Working with Other Languages
Introduction
Calling Java methods and accessing Java objects from Clojure
Extending Java superclasses and implementing Java interfaces
Calling Clojure from Java
Calling Scala from Clojure
ClojureCLR
ClojureScript
6
6. Concurrency and Parallelism
6. Concurrency and Parallelism
Introduction
Solving concurrent problems using Clojure
Distributed actor-based dev with Akka
Using Spyglass and Couchbase to share state between JVMs
Reactive programming with meltdown
Bridging core.async
On Quasar/Pulsar
7
7. Advanced Tips
7. Advanced Tips
Introduction
Hacking the Clojure code
Using Reader Conditionals, compile to Clojure, and ClojureScript
Real-time shared development with an REPL
Declarative data descriptions and validations with plumatic/schema
8
8. Web Applications
8. Web Applications
Introduction
Clojure with Vaadin - easy web widgets
Quickly create a REST API with Liberator
Working with Immutant - reusing infrastructure
Developing with om.next, the next-generation ClojureScript library
9
9. Testing
9. Testing
Introduction
Behavior-driven development
Testing with random inputs and pattern-based testing
Benchmarking with Criterium, performance tips, and other tools
10
10. Deployment and DevOps
10. Deployment and DevOps
Introduction
Riemann - monitoring deliverance and slacking
Deploying Clojure with Docker
Clojure on Amazon Web Services

Accessing and updating elements from collections

In this recipe, we will teach you how to access elements and update elements in collections.

Getting ready

You only need REPL, as described in the recipe in Chapter 1, Live Programming with Clojure, and no additional libraries. Start REPL so that you can review the sample code in this recipe.

How to do it...

Let's start with accessing collections.

Accessing collections using the nth function

nth gets the nthelement from collections. The second argument of nth starts from 0 and throws an exception if the second argument is larger than the number of elements minus 1:

(nth [1 2 3 4 5] 1) 
;;=> 2 
(nth '("a" "b" "c" "d" "e") 3) 
;;=> "d" 
(nth [1 2 3] 3) 
;;=> IndexOutOfBoundsException   clojure.lang.PersistentVector.arrayFor (PersistentVector.java:153)

If you would like to avoid such an exception, use the third argument as the return value:

(nth [1 2 3] 3 nil) 
;;...

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