“Pushy” is a new name for an old scheme that was invented circa 1973 for Tymnet but not implemented. (I want a better name.) Its external functionality seems somewhat like SVR4 streams (.ps) (Sun’s version). There are significant differences however and so I report the original idea here, a recent transcription of the ideas as I recall them. Its design has not been recorded before (1999), and only a few people have heard of it as of 1999, at least from me.

Raoul Duke just brought to my attention the Flow-based programming patterns which are certainly an earlier publication of ideas much like these.
The Click suite illustrates the use of similar ideas to packet processing.
Here are recent comparisons with some modern programming patterns.
Here is a scheme inspired by Henry Baker that discards the built in continuations, and a similar independent C version.

Brief note on doing this with Keykos domains.
OCaml is promissing.

Some Theory or formalism
issues
splitting a stream