How to Make a Process Invisible

Sometimes it is useful to be able to invisibly splice a process into a channel, allowing it to observe (log or present to a GUI) communications on the channel without breaking the synchronous communication semantics. occam-pi's extended rendezvous when reading from a channel made this possible: the invisible process could keep the writer waiting until the real reader had accepted the forwarded communication. This breaks down when it is possible to have choice on outputs (also known as output guards). An extended rendezvous for writing to a channel fixes this aspect but in turn does not support choice on the input. It becomes impossible to keep your process invisible in all circumstances. This talk explains the problem, and proposes a radical new feature that would solve it.