Coroutines in C (go macros)

count.c

//
// count.c
//
// Based on a a Duff's device
// https://pusher.com/sessions/meetup/the-realtime-guild/realtime-stream-processing-with-coroutines
//

#define go static int __resume__ = 0; \
  if (__resume__) goto __RESUME__;

#define yield(value) do { if (!__resume__) __resume__ = 1; \
  return value; __RESUME__:; } while (0)

/*
 * Count numbers.
 */

int
count() {
  go {
    static int n = 0;
    while (1) {
      yield(n++);
    }
  }
}

/*
 * Run program.
 */

int
main() {
  printf("%d\n", count()); // 0
  printf("%d\n", count()); // 1
  printf("%d\n", count()); // 2
}