> Particularly for error handling, you always want to see what errors a function may return even in library code. Any half-decent tooling should do that, since

> Particularly for error handling, you always want to see what errors a function may return even in library code. Any half-decent tooling should do that, since GP was talking about compile-time type inference. Of course there are some situations where the type hints aren't available, but then we're back to a general discussion about type inference. FWIW, I don't actually agree with the idea that set-theoretic unions solve error handling, but I'm fully on-board with opt-in type inference for errors.