Earlier quoted context omitted.
Why async/await is not a good thing? What makes green threads better? Do you know the difference, the issues async/await addresses that green threads simply do not?
This is code with async/await: async fn read_file(filename): f = await os.open(filename) let data = f.read() await f.close() return data this is equivalent code with green threads: fn read_file(filename): f = os.open(filename) let data = f.read() f.close() return data As you can see, async/await is pure syntactic noise, it doesn't convey any important meaning.
Better implementations offer eager execution and allow to easily interleave multiple concurrent futures/tasks, like C#. Green threads on the other hand are a workaround to deal with blocking for the most trivial case of cooperative multi-tasking, offering little beyond that.