If you haven't seen it already you should check out Peter Norvig's 20-odd line toy spell checker, written over the course of a flight.
Edit: forgot the link https://github.com/dlang/dmd/blob/master/src/dmd/root/spelle...
https://github.com/dlang/dmd/blob/master/src/dmd/root/spelle...
This is a spell-checker in the D reference compiler that detects typos in identifiers and suggests potential corrections for those typos.