Await_kernel.YieldA value of type t allows cooperatively yielding to the scheduler. Operations that run long computations and might want to yield to a scheduler take a t that provides an implementation of yielding for them to use.
Internally, a Yield.t is just an Await.t, but code which only yields and does not block can take a Yield.t as a parameter to promise that it will not block.
of_await await is an implementation of yielding based on await
val yield : t @ local -> unit @@ portableyield t uses t to yield to the scheduler