[kaeluka]

I was confused -- how can a library add a keyword like "coroutine" to C. It didn't look like macros were powerful enough to do that (I expected to at least some context having to be passed to the worker, or so).

It turns out that a coroutine is just a function that the compiler should not inline: https://github.com/sustrik/libmill/blob/master/libmill.h#L24...

[rumcajz]

Yes, it's just a normal function. What go() macro does is that it switches the stack, then lets compiler-generated code put the args of the function at the top of the new stack. Obviously, if the function was inlined, the above would not work.