I often use NaNs on purpose to designate “unknown”, and its properties of “infecting” computations mean that I don’t have to check every step - just at the end

I often use NaNs on purpose to designate “unknown”, and its properties of “infecting” computations mean that I don’t have to check every step - just at the end of the computation. R goes even farther, and uses one specific NaN (out of the million-billions) to signal “not available”, while other NaNs are just NaNs. Its properties, used properly, make code much more simple and sane.