(defer-yield on-pause on-resume)
  on-pause: any form
  on-resume: any form

Defers evaluation until a coroutine is paused and/or resumed.

This special form is a complement to defer. It evaluates one form every time it goes out of scope because its coroutine was paused, and evaluates another form every time it comes back into scope because its coroutine was resumed. (Under those circumstances, a defer form would not be evaluated.)

When defer-yield appears outside of a coroutine, it's a silent no-op.