Intro to Clojure on the Web

Reuven Lerner — Thu, 31 Oct 2013 19:07:39 +0000

Lisp is one of those languages that people either love or hate. Count me among the Lisp lovers. I was brainwashed during my undergraduate studies at MIT to believe that Lisp is the only "real" programming language out there, and that anything else is a pale imitation. True, I use Python and Ruby in my day-to-day work, but I often wish I had the chance to work with Lisp on a regular basis.

One window of opportunity to do exactly that has opened in the past few years. Clojure, a modern variant of Lisp that runs on the Java virtual machine (JVM), has been taking the programming world by storm. It's a real Lisp, which means that it has all of the goodness you would want and expect: functional programming paradigms, easy use of complex data structures and even such advanced facilities as macros. Unlike other Lisps, and contributing in no small part to its success, Clojure sits on top of the JVM, meaning that it can interoperate with Java objects and also work in many existing environments.

In this article, I want to share some of my experiences with starting to experiment with Clojure for Web development. Although I don't foresee using Clojure in much of my professional work, I do believe it's useful and important always to be trying new languages, frameworks and paradigms. Clojure combines Lisp and the JVM in just the right quantities to make it somewhat mainstream, which makes it more interesting than just a cool language that no one is really using for anything practical.

Clojure Basics

Clojure, as I mentioned above, is a version of Lisp that's based on the JVM. This means if you're going to run Clojure programs, you're also going to need a copy of Java. Fortunately, that's not much of an issue nowadays, given Java's popularity. Clojure itself comes as a Java archive (JAR) file, which you then can execute.

But, given the number of Clojure packages and libraries you'll likely want to use, you would be better off using Leiningen, a package manager for installing Clojure and Clojure-related packages. (The name is from a story, "Leiningen and the Ants", and is an indication of how the Clojure community doesn't want to use the established dependency-management system, Ant.) You definitely will want to install Leiningen. If your Linux distribution doesn't include a modern copy already, you can download the shell script from https://raw.github.com/technomancy/leiningen/stable/bin/lein.

Execute this shell script, putting it in your PATH. After you download the Leiningen jarfile, it will download and install Leiningen in your ~/.lein directory (also known as LEIN_HOME). That's all you need in order to start creating a Clojure Web application.

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