With the result of a read or write being *returned*, there's now an ambiguity as to whether the caller is prepared to handle partial success. I'm experimenting with a notation change, so that invocations where the caller expects an except to be thrown on failure have a 'Must' suffix, and where we're planning to handle the return value there's a 'Q' prefix. But this this make a mess of some preexisting code. So, this is very much a work in progress.