// f: func -> A | endMarker
static <A> IterableIterator<A> iff(O f) {
  ret iteratorFromFunction_withEndMarker(f);
}

// can't use type parameter because end marker
static IterableIterator iff(F0 f) {
  ret iteratorFromFunction_withEndMarker(f);
}

static <A> IterableIterator iff(IF0 f) {
  ret iteratorFromFunction_withEndMarker(f);
}