Yes We Controlled A Rover

I'm just recovering from this weekend's ICFP Programming Contest in which we had to write a controller for a simulated Mars Rover. I'm pretty sure we're not winning anything, even assuming we ever get Mathematica in the hands of the contest organizers. After the rules were announced the week before, I frantically went around trying to figure out if we could even enter a contest with Mathematica, a commercial product that requires a license key to run, finally coming up with two workable options. Only to discover on Saturday that one of the options wasn't going to work because the submission form was capped at 20MB. I had counted on being able to upload a stripped down copy of Mathematica weighing in at around 140MB. The contest staffer on the IRC chat channel told me we would work it out later.

We used Java to do the socket stuff, and JLink to go between Java and Mathematica. This isn't as hard as it might sound, and especially as all three of us on the team develop Java/Mathematica hybrid products (Wolfram Workbench is Eclipse-based and webMathematica works with Tomcat).

The code we worked on during the contest had Java in control and called Mathematica to process each event from the server (i.e. the rover). This worked fine, but I wish I'd listened more carefully to the 3 senior people at work who advised Mathematica be in control and call Java.

Last night I inverted the control and rewrote the little event loop in Mathematica, and suddenly the light went on that we really missed out by not having the Mathematica front end part of our interactive development process. I was quickly able to write a Dynamic-based dashboard: literally we could watch the controller's state updated in real time, including calculated state. We saw things like instantaneous speed, heading, and the rover's steering and acceleration state. It seems it would have been so much more helpful to see these numbers as our rover wandered around, to get more familiar with the problem. As it was we stared at static log files of telemetry messages after the run was over.

I hope I can write a little more about our experience later. It was fun though.