Neander has no exceptions. No try , no catch , no finally . A call to one of the host application's APIs returns something closer to Rust's Result : either the answer, or the reason there is no answer. In place of a catch block there is one type marker, three operators, and a guarantee that every submission comes back in the same shape no matter what happened. Last time the foundational series closed with isolation. This is the first of two encores, and it takes the subject that came up...