iter pairs() -> tup(int,int) {
  let int i = 0;
  let int j = 0;
  while (i < 10) {
    put tup(i, j);
    i += 1;
    j += i;
  }
}

fn main() {
  let int i = 10;
  let int j = 0;
  for each (tup(int,int) p in pairs()) {
      log p._0;
      log p._1;
      check (p._0 + 10 == i);
      i += 1;
      j = p._1;
    }
  check(j == 45);
}