Book Review: Clojure Cookbook

The Clojure Cookbook is part of the O’Reilly cookbook series. I’d describe this format as a ‘curated wiki in print’. The wiki analogy is especially true for this volume since its contents were contributed by some 60 different developers. It’s packed with small, bite-sized recipes for solving common problems in Clojure. This is useful for developers across the entire spectrum from beginner to expert.

The content is organized into 11 chapters, each containing a number of recipes. The chapter layout is clear and serves its purpose when looking for content. The book covers a lot of ground, from working with primitives and basic data structures to dealing with databases, writing web apps, and running Hadoop jobs. Each recipe comes with code and/or REPL examples, so it’s very easy and enlightening to ‘play along’. In contrast to other books with code snippets, the authors have made all recipes self-contained (no other projects/files need to be created and run for the examples to work), which makes it very easy to dive in at any point in the book.

Each recipe also contains a reference section, often this is a URL to a javadoc and, in some cases, references to other books and resources. This makes the Clojure Cookbook perfect for your first port of call when tackling a given problem – if you want to dig deeper, the references are a good starting point.

Some sections stand out to me, for example the sections on DateTime (which is always a headache in Java/Clojure) are rich, clear and very helpful. Implementing a Red-Black tree and parsers with core.match is interesting. The core.logic example is perfect primer for anybody wanting to come to grips with logic programming. Speeding up IO with reducers I also found very enlightening. The datomic recipes are actually easier to understand than most of datomic’s own documentation.

There are some drawbacks with the ‘wiki in print’ approach. I made quite a few notes while reading the book, and I believe material like this should evolve and improve over time. For instance the part of mean/medium/standard-deviation should have a snippet on percentiles, and the part on generating random numbers should talk about secure randoms. It would be great to see this material on a wiki as well as in print. The clojure docs site is in desperate need of a refresh and a lot of the material in this book would be a perfect starting point.

I warmly recommend this book to all Clojure developers of any skill level. I suggest beginning with a proper read-through and then keeping a copy handy for looking up stuff when you need it. Chances are that after the first read-through, you (like me) immediately go back and clean up some of recent code.

This book will make you a better Clojure developer.