[pcwalton]

The main reason behind the panic/Result distinction is that systems programmers, particularly those working in embedded, want to be able to turn off unwinding support entirely. Unwinding adds control flow edges everywhere, inhibiting optimizations, and it either adds code size bloat for the unwind tables or runtime overhead at every function call, depending on how it's implemented. I don't know of any way to implement exceptions that doesn't have this overhead. So although I like exceptions myself, I agree with Rust's decision not to embrace them in its domain.