How did we end up with printf - within a loop - being Turing-complete? Was it designed that way from the beginning? Were new features added over time until we got there?
Having something Turing-complete is surprisingly easy, and it hides everywhere. The repository have a small document that explains how you can use printf() as a computer : it can performs additions, logical union and negation, which is enough.
It was unintentional, but Ken Thompson being Ken Thompson, can't be 100% sure.
It was probably unintentional, yeah, I don't recall any mentions of early printf being overloaded to do stuff, nor is it clear why you would do that since you're using it in a much more convenient Turing-complete language already (C).
