I'm working on landing a similar feature in a language project, but in a general way, geared torward high level application flows. The general idea is that you can declare a "seam" between a function that returns a type set, and some other actor that exposes a method set that covers said typeset. The compiler can deal with the inbetween code, so the mainline of the app is just a set of typespace expansions/compressions. A callstack within a single thread domain can be expressed like:

bytes → (NewOrder | Cancel) → handlers → (Ack | Reject) →

https://github.com/hale-lang/hale/issues/1530#issuecomment-6...