electronic music in Scheme with impromptu

Here's a neat project that got mentioned over the plt-scheme mailing list at some point: impromptu, a Scheme/OSX-based electronic music environment. I've been casually interested music-specific programming languages for a while, but up until now the best thing I'd found was CSound which doesn't thrill me.

My main reason for being interested is that I think music could be a very natural way to teach students about higher-order functions: a sound is a function from time to frequency, and all sound operations become function composition. Want to make a 5-second sound clip last 10 seconds instead? It's a one-liner. Want to shift the pitch up or down? Just as easy. Want to do both? No problem. I think it's a really natural way to think about sound that leads just as naturally to higher-order functions, and that's pretty cool. It's also the sort of thing I can imagine one or two kids really nerding out over, which is definitely a bonus.