I'm not sure I agree that it's necessarily bad if the interface is a side-effect of the implementation. It seems very worse-is-better to me. I feel like when

I'm not sure I agree that it's necessarily bad if the interface is a side-effect of the implementation. It seems very worse-is-better to me. I feel like when the interface is a side-effect of implementation, you get a more gradual sliding scale from user to developer (like being able to experiment with web apis by curling at them). In git's case, I appreciate that I can trawl around through my .git directory and not get lost because it pretty closely matches the interface.