Just on this point:
reply> You mean like how Rust tried green threads pre-1.0? Rust gave up this one up because it made runtime too unwieldy for embedded devices.
The idea with making std.Io an interface is that we're not forcing you into using green threads - or OS threads for that matter. You can (and should) bring your own std.Io implementation for embedded targets if you need standard I/O.
Ok. But if your program assumes green threads and spawn like two million of them on target that doesn't support them, then what?
replyThe nice thing about async is that it tells you threads are cheap to spawn. By making everything colourless you implicitly assume everything is green thread.