Book Image

Clojure Programming Cookbook

Book Image

Clojure Programming Cookbook

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 (16 chapters)
Clojure Programming Cookbook
About the Authors
About the Reviewer

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 nth element 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 ( 

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

(nth [1 2 3] 3 nil) 
;;=> nil 

Notice that nth does not...