There is also a case to be made that being able to debug without a debugger is actually very useful for someone who works in compilers, because often, there is no debugger available. Most of the bugs I had to find in this case weren't crashes, but type inference errors caused by complex interactions in multiple areas of the system. Debugging complex systems can be difficult, and I often find that the best strategy is to work to prevent latent bugs using unit tests and assertions, but that's a story for another time.