You still need to signal the absence of a value. This is not necessarily the same thing as a monadic Return<R, E> type as in Rust, which I quite like and would

You still need to signal the absence of a value. This is not necessarily the same thing as a monadic Return<R, E> type as in Rust, which I quite like and would prefer over exceptions. I think the Kotlin solution is very elegant, considering the restrictions of the host platform of using exceptions as error signaling mechanism.