@Test
public void testLazyMapIndex() {

  List<Integer> eval = mlazy(asList(1, 2, 3, 4, 5)).mapIndex(new Function2<Integer, Integer, Integer>() {
    @Override
    public Integer apply(Integer n, Integer i) {
      return n + i;
    }
  }).eval();
  assertArrayEquals(new Integer[]{1, 3, 5, 7, 9}, eval.toArray(new Integer[]{}));
}