> generally, the most common function is going to be along the lines of "I know this is positive, so throw an error if it's 0"—which is exactly what we get anyw

> generally, the most common function is going to be along the lines of "I know this is positive, so throw an error if it's 0"—which is exactly what we get anyway. That's still a lot better than before. It's not too hard to read a function and be reasonably confident that it will always return a positive value. On the other hand, it's pretty hard to audit an entire codebase to make sure a value can never be negative, or something like that. The main difference is probably only needing to do that audit once, when writing the function, instead of every time you need to rely on the function's return value being positive. It would also save a lot of work because a lot of operations _can_ be detected automatically. positive * positive = positive, etc. So you would only have to manually assert in the cases it wouldn't be doable automatically, which would be significantly fewer than before.