static <A> IterableIterator<A> filterIterator(final Iterator<A> it, final F1<A, Bool> f) {
  if (it == null) null;
  ret iff(func -> O {
    while (it.hasNext()) {
      A a = it.next();
      if (callF(f, a))
        ret a;
    }
    ret endMarker();
  });
}

static <A> IterableIterator<A> filterIterator(final Iterator<A> it, final IF1<A, Bool> f) {
  if (it == null) null;
  ret iff(func -> O {
    while (it.hasNext()) {
      A a = it.next();
      if (callF(f, a))
        ret a;
    }
    ret endMarker();
  });
}

static <A> IterableIterator<A> filterIterator(final F1<A, Bool> f, final Iterator<A> it) {
  ret filterIterator(it, f);
}

static <A> IterableIterator<A> filterIterator(Cl<A> l, IF1<A, Bool> f) {
  if (l == null) null;
  Iterator<A> it = iterator(l);
  ret iff(func -> O {
    while (it.hasNext()) {
      A a = it.next();
      if (f.get(a))
        ret a;
    }
    ret endMarker();
  });
}

static <A> ItIt<A> lambdaMapLike filterIterator(IF1<A, Bool> f, Iterator<A> it) {
  ret filterIterator(it, f);
}

Began life as a copy of #1014420