# this version uses the "process" structure,
# and a simple scheduler

use stdio.h

struct process
typedef int (*process_func)(process *p)
struct process
	process_func f
	int pc
	void *data

int count_to_three(process *p)
	switch p->pc
	0	printf("1\n")
		return 1
	1	printf("2\n")
		return 2
	2	printf("3\n")
		return 3
	3	.
	return -1

struct count_to_n_data
	int n
	int c
int count_to_n(process *p)
	count_to_n_data *d = (count_to_n_data *)p->data
	switch p->pc
	0	d->c = 1
		while d->c <= d->n
			printf("%d\n", d->c)
			++ (d->c)
			return 1
	1		.
	return -1

# will have to consider how to implement "child" or "sub-" processes

using namespace std

use deque

int main()
	process c3 = { count_to_three, 0 }
	while c3.pc != -1
		c3.pc = (*c3.f)(&c3)

	count_to_n_data d1, d2
	process cn1 = { count_to_n, 0, &d1 }
	process cn2 = { count_to_n, 0, &d2 }
	d1.n = 10
	d2.n = 15

	deque<process *> q
	q.push_back(&cn1)
	q.push_back(&cn2)

	while !q.empty()
		process *p = q.front()
		q.pop_front()
		int pc = (*p->f)(p)
		if pc != -1
			p->pc = pc
			q.push_back(p)

	return 0