def weirdFold[T,B](s:List[T], init:B, f:(T,List[T], B) => (T,B)) = {
    def helper(s:List[T], b:B, i:Int) = {
      val ts = s.toVector
      if (i > ts.length - 1) {
        (s, b)
      } else {
        val t = ts(i)
        val (newT, newB) = f(t, s, b)
        (ts.updated(i, newT), newB)
      }
    }
    helper(s, init, 0)
  }