!7

p-subst {
  repeat with sleep 1 {
    currentImage(newBufferedImage(200, 200, Color.gray));
    Rect r = randomRect();
    Pair<Rect> p;
    if (tossCoin()) {
      r.h &= ~1; // make even
      p = splitRectInVerticalHalves(r);
    } else {
      r.w &= ~1; // make even
      p = splitRectInHorizontalHalves(r);
    }
    if (oneInTwoChance()) p = reversePair(p);
    fillRect(p.a, Color.black);
    fillRect(p.b, Color.white);
    quickShowImage();
  }
}