static int smartIndexOfSpacedDash(L<S> x) {
  ret smartIndexOfSpacedDash(x, 0);
}

static int smartIndexOfSpacedDash(L<S> x, int i) {
  outer: for (i |= 1; i+2 <= l(x); i += 2) {
    if (eq(x.get(i), "-") && nempty(x.get(i-1)) && nempty(x.get(i+1)))
      ret i;
  }
  ret l(x);
}