Code walkthrough in Hickey presentation

December 6, 2008

**Update 12/11/2008: In the original post, I claimed the code from Hickey’s presentation needed to be updated to the latest version of Clojure. Wrong. The code wasn’t running for me because I didn’t have the de facto latest version, which is built from subversion. I’ve edited the post to reflect this. **

Hickey’s presentation to the Western Massachusettes Developers Group is primarily about Concurrency. The first half covers similar topics to his other presentations (including the For Lispers presentation). But about halfway through the talk, at 1:16:00, he begins a walkthrough of a program he wrote simulating an ant colony. I really recommend following this. It’s helped me a lot.

So go view the video:

Get the code for the simulation too, from the link on the Blip page. As of this posting, you’ll need to build clojure from subversion to make the code work. If you’re using the latest official release, from September 16, you’ll need to use a copy of the code I made: http://groups.google.com/group/clojure-study-dc/web/ants.clj.

The key difference is in the java interop syntax. The latest version of clojure uses a dot before a method call in many circumstances, whereas the official release does not. In other words:

(doto g
    (.setColor c) ;; current syntax, with dot
    ...

vs.

(doto g
    (setColor c) ;; official release syntax, no dot.
    ...

If you run current Clojure code using the official release, you’ll see a lot of errors like these:

java.lang.IllegalArgumentException: No matching method found: 
  .setPreferredSize for class clojure.lang.Proxy__2845

The walkthrough takes about an hour. Give it a try.