But since you are asking me to download the language so politely: I think this is not necessary. A look in the documentation (https://docs.raku.org/language/concurrency) seems to be enough:
> The subroutine await is almost equivalent to calling result on the promise object returned by start but it will also take a list of promises and return the result of each
So "await" is equivalent to calling "result". What does calling "result" do?
> result blocks the current thread of execution until the promise is kept or broken
This stands in direct contradiction to what was said in the thread here:
> so while the code containing the `await` blocks and waits, the underlying thread/core is released
Unless the OP referred to a _different_ await, I would say: case closed.
> blocks the current thread of execution
That's a green thread.[1]
To quote Wikipedia[2]:
> a thread of execution is the smallest sequence of programmed instructions that can be managed independently by a scheduler
This is the definition the doc is using.
The thread of execution that is blocked is a green thread -- the sequence of instructions containing the `await` that is managed by a scheduler managed by Raku.
> This stands in direct contradiction to what was said in the thread here:
>> so while the code containing the `await` blocks and waits, the underlying thread/core is released
> Unless the OP referred to a _different_ await
No, what I meant by "underlying thread/core" is an OS thread as against a green thread, and what I meant by "released" wasn't that it was released back to the OS but instead that Raku's scheduling sees the `await`, blocks the enclosing green thread, and immediately unblocks some other green thread by "stealing"[3] the OS thread to run that other green thread instead.
I hope I've now reassured you that Raku(do) both eliminates the red/blue distinction and doesn't block OS threads.
Yes, it's unusual among PLs. No, it's not easy to design a PL to do this at a language level. Nor is it easy to implement. (For example, the Rakudo implementation involves taking a continuation[4].)
But it is possible, and Raku has never had the red/blue distinction, and has had work stealing semantics for `await` since 2018.
[1] https://en.wikipedia.org/wiki/Green_threads
[2] https://en.wikipedia.org/wiki/Thread_(computing)
[3] https://en.wikipedia.org/wiki/Work_stealing
[4] http://jnthn.net/papers/2018-concurrency-guts.pdf#page=67
