(Co)routines

[giann]

Implement coroutines

import "lib/std";

fun main() > void {
    | Async call, creates a new routine (new VM instance), count is not yet executed
    rti<str, num> counter = async count(10);

    | A routine is over when a OP_RETURN as been executed
    while (!counter.over()) {
        print("counter is {resume counter}");
    }
    
    assert(counter.over(), message: "Routine should be over now");
    
    | await either runs the routine until completion or get the return value of a terminated routine
    | if the function yields but is never resumed when we reach the await, yields value are dismissed (?)
    print(await counter);
}

| returns str, yields num
fun count(num n) > str > num {
    for (num i = 0; i < n; i = i + 1) {
        | error or yield is ignored if not called with a async call?
        yield i;
    }

    return "Counting is done!";
}