static SS parseDoubleRightArrowMap(SS map, L<S> l) {
  ifdef debug_parseDoubleRightArrowMap
    print("parseDoubleRightArrowMap: " + l);
  endifdef
  for (S s : l) {
    L<S> x = splitAtDoubleArrow(s);
    if (l(x) == 2) map.put(first(x), second(x));
  }
  ret map;
}