Finite Improbability

Wow, I can’t believe I’ve let posting about this slip so far. I have been working on the game, just not as much as I would have liked. Obviously I haven’t been keeping up with my nonexistant readers about it.

The bits of time I could snatch to work on my game have mostly been spent building up a decent logging infrastructure. Simple things like hunting down a null pointer exception become grossly complicated now that I have two different language environments passing code between each other. Logging helps, and thanks to the power of Lisp I can write some pretty useful logging code. Here’s a sample:

(with-log "Failed to update an ant position"
 (update-pos ant))

This expands into a bunch of stuff, but basically any exception thrown in the code run by with-log is trapped, the message “Failed to update an ant position” is logged (as an error by default) and the exception is rethrown. Pretty basic I guess. Here’s where this really comes into play. When the game detects an exception that I could presumably fix without needing to restart it pauses. I can then modify any of the game code and my new code will run when I unpause the game. This combined with the logging code above lets me hunt through my code to pinpoint where the exception is being thrown. From there I can start working bacwards through the function call stack and instrument each function call to test for and log null arguments. Eventually I’ll pinpoint where my null argument originates and can fix that.

I’m planning on expanding the logging facility so it will only track certain errors. The idea is that I could write something like this:

(with-log
 [(NullPointerException "Null pointer encountered in foo")
 (BoredAntException "An ant has nothing to do")
 (OverthoughtExampleException "This example is gratuitous")]

 (code...))

One of the beautiful things about working with Lisp is that you can imagine how your program would be written in an ideal psuedocode, write it that way, and build up from your existing language to that one.

Anyways, in addition to writing logging code I’ve started implementing the steering and seeking behavior described here: http://www.red3d.com/cwr/steer/gdc99/

When I started it was working pretty well, but I managed to introduce some bugs that were pretty hard to track down. So, now that I have a better bug handling infrastructure I can get back to the fun part.

Update:

After I finally finished setting up my logging system I identified and solved my problems pretty quickly. The steering behavior didn’t take very long to perfect so I now have a good portion of the game implemented. At the least the ants are moving from A to B pretty consistently, although I’ll probably have to come up with a good mix of the steering and arrival code to simulate the ants picking at a piece of food.