I've been rather interested in koans as a learning method, and recently I've started delving into theory-intensive topics like compilers (I have a copy of Dragon and I'm looking at buying a copy of Appel's ML book). However, I'd like to strengthen my code-grokking abilities (and a fair bit of the theory makes my eyes glaze over anyway). The only koans I've been able to find are for programming languages. Are there any koan(-type) lessons for things like compilers, operating systems, etc?