Very often the journey with Clojure starts like this. You notice its growing popularity or want to attach a new tool to your belt. So you go through some quick introduction, learn the basics, get a few programs running… And eventually ask yourself: Fine, but what’s next? What’s the difference? How does one really work with Clojure?
That’s where The Joy of Clojure by Michael Fogus and Chris Houser enters the play. The goal of this book is to provide answers to these fundamental questions and teach you “The Clojure Way”.
It starts with an explanation of what Clojure is and the problems that it solves. Then it provides an overview of the language: data types, functions, collections, destructuring, composite data types and lazy evaluation. Finally it explores more advanced concepts: functional programming, metaprogramming, performance, mutation, concurrency and parallel programming.
However, by no means is it an average reference / language overview book. What it really does is explain the philosophy of LISP, functional programming and last but not least Clojure, and only then discuss all the technical stuff.
Just because the primary focus is not syntax and low-level technical details does not mean they are not explained in depth. Nothing is missing: syntax, performance, intricate details of data types and other constructs – they’re all here.
That’s where the book really shines. It’s easy to write a manual that describes a technology, but fails to describe its purpose. “The Joy of Clojure” managed to explain what Clojure really is, with all its fundamentals and idioms.
The major downside of the book is that some of the advanced low level technical / syntactical aspects are explained in a rather steep, if not discouraging way. Take macros for example. The concept is clear, but the examples could be less complicated and it falls short of explaining the basic syntax.
If you’re looking for an easy basic introduction to Clojure, or a practical guidebook on libraries, developing web apps etc. then probably this is not the best choice. But if you are up for a challenge or know some Clojure and are asking yourself the fundamental questions from the first paragraph of this review, you are going to love it. Sometimes it is steep and demanding, it may require you to reread some of the chapters later, but it definitely is worth it.
Note: This review is based on an early access edition provided by Manning Publications Co. The estimated publishing date is December 2010, but you can get a pre-release PDF already from Manning Publications.