I'm interested in the Clojure programming language and the Google App Engine platform right now, and I'm playing around with the combination of both. Since there isn't a whole lot of information on this on the net, I thought I'd share the results of my experiments in this blog. Here's the rundown on what this will (and won't) be about:
Clojure is a functional programming language of the Lisp family, designed with concurrency in mind to make it easy to write multi-threaded programs. It runs on the Java Virtual Machine and can call (and be called from) Java code. I'm not going to write a tutorial on programming Clojure (many others can do this better than me) nor am I going to try to convince you that Clojure is the greatest language in the world. I just think it's very interesting and I assume you do, too - otherwise you probably wouldn't have stumbled across this site. If you want to learn more about Clojure, the official website provides very good documentation. I highly recommend watching the videos of Rich Hickey's talks, they got me hooked in the first place.
Compojure is one of the frameworks for developing web applications in Clojure that are being developed right now. I don't know if it's the best, but it's the one I'm playing around with. The documentation isn't very extensive, but you can find some at http://preview.compojure.org and there's an active Google group. You can grab the code at GitHub. For getting started I recommend this short tutorial by Compojure's creator, James Reeves.
Google App Engine (GAE) is a service provided by Google that let's you develop web applications that can be deployed to Google's server infrastructure. Google provides several APIs that applications can use, e.g. for user authentication and storing data in a distributed data store. The idea is that applications can easily scale to handle everything from very small to very large loads. When App Engine was initially released it only provided a Python runtime environment. In April 2009 the Java runtime for App Engine was introduced. This opened the door not only for Java programs but for a number of languages that run on the JVM, including Clojure.
I chose to implement a little blogging application to experiment with Clojure/Compojure on GAE. This isn't very exciting at all and I don't intend to actually use it. But it is simple and straightforward and displays much of the functionality of a typical web app: displaying pages, handling form input, storing and retrieving persistent data and authenticating users. (Edit: After reading this question on stackoverflow I feel a little bad about my choice of example app. But at least I'm in good company...)
So, that's the plan. In the next post I'll talk about setting up the development environment.