Okay, the programming contest is up now. Fun! People all over the world are now (possibly) chuckling at all the stupid little jokes we wrote in and (probably) puzzling their way through the gawdawful rules text that we couldn't figure out how to get rid of. On the plus side, it's now 13 hours in and the worst thing that has happened so far is that there've been some platform-specific problems with the support code we provided and we accidentally let slip that that game had to do with cops and robbers a bit early. Considering that we've been thinking about the game in more or less this form since, um, at least January or so, it's pretty good that we didn't let more than that out. It seems to be pretty well-received, though we're going to have to wait for the submissions to roll in and particularly for the second phase to really see whether we succeeded or not. But for right now, I'm just pleased that things have gone so smoothly — I have to say I was more or less imagining this whole ordeal somehow managing to set all our offices on fire and burn down our building.

In the midst of the contest going up, I also had to teach one of the key HtDP lectures: the dreaded "lists" lecture. Introducing kids to the notion of recursive data structures and recursive functions all in one fell swoop and making it seem natural is a pretty tough trick, and I was definitely not sure I could do it. I eased them into it using a trick I got from Matthew and Robby: you first give a "brain-teaser" of how to store two numbers in a box structure that has a left and a right; then you ask how to store four numbers using boxes (just store two copies of your solution for two numbers); then 8. 16, and so on. Then you ask how to store 5 numbers in a box (make a new box with a number on the left and your 4-number box on the right), then how to do six (repeat the same process), then 7 and so on. Then ask how to store one number, and relatedly how to store zero numbers. At that point, you've developed the idea behind linked lists on the board.

This strategy seemed to work as well as I could've hoped; some people looked kind of blown away, others really took to it, and some people thought it was kind of obvious, but everyone seemed to be able to grasp cons lists by the end of the lecture. We'll see how well they did it when the homeworks come in, of course, but people were answering my questions in class, so that's something.