static L<S> splitAtDoubleArrow(S s) {
  ret splitAtDoubleArrow(javaTok(s));
}

static L<S> splitAtDoubleArrow(L<S> tok) {
  new L<S> l;
  int i = 0;
  while (i < l(tok)) {
    int j = indexOfSubList(tok, splitAtDoubleArrow_tok(), i);
    if (j < 0) j = l(tok);
    l.add(trimJoin(tok.subList(i, j)));
    i = j+3;
  }
  ret l;
}