Book Image

The Clojure Workshop

By : Joseph Fahey, Thomas Haratyk, Scott McCaughie, Yehonathan Sharvit, Konrad Szydlo
Book Image

The Clojure Workshop

By: Joseph Fahey, Thomas Haratyk, Scott McCaughie, Yehonathan Sharvit, Konrad Szydlo

Overview of this book

The Clojure Workshop is a step-by-step guide to Clojure and ClojureScript, designed to quickly get you up and running as a confident, knowledgeable developer. Because of the functional nature of the language, Clojure programming is quite different to what many developers will have experienced. As hosted languages, Clojure and ClojureScript can also be daunting for newcomers because of complexities in the tooling and the challenge of interacting with the host platforms. To help you overcome these barriers, this book adopts a practical approach. Every chapter is centered around building something. As you progress through the book, you will progressively develop the 'muscle memory' that will make you a productive Clojure programmer, and help you see the world through the concepts of functional programming. You will also gain familiarity with common idioms and patterns, as well as exposure to some of the most widely used libraries. Unlike many Clojure books, this Workshop will include significant coverage of both Clojure and ClojureScript. This makes it useful no matter your goal or preferred platform, and provides a fresh perspective on the hosted nature of the language. By the end of this book, you'll have the knowledge, skills and confidence to creatively tackle your own ambitious projects with Clojure and ClojureScript.
Table of Contents (17 chapters)
Free Chapter
2
2. Data Types and Immutability

Using Lazy Sequences

Before we move on, it's important to take a closer look at how lazy sequences work in Clojure. When using map and filter, lazy evaluation is often an important consideration. In the examples we've looked at so far, we have used a literal vector as input: [1 2 3 4 5]. Instead of typing out each number, we could use the range function and write (range 1 6). If we type this in the REPL, we get basically the same thing:

user> (range 1 6)
(1 2 3 4 5)

So, is this just a shortcut to avoid typing out lots of integers? Well, it is, but range has another interesting characteristic: it's lazy.

Before we go further, let's revisit laziness briefly. If (range 100) is a lazy sequence, that means that it is not realized until each element in the sequence has been calculated. Say we define a lazy sequence from 0 to 100:

user> (def our-seq (range 100))

Note

The REPL causes lazy sequences to be evaluated. This can be confusing sometimes...