def weirdFold[T,B](s:List[T], init:B, f:(T,List[T], B) => (T,B)) = {
    var ts = s.toVector
    var v = init
    for (i <- 0 until ts.length) {
      val t = ts(i)
      val (newV, newT) = f(t, ts.toList, v)
      v = newV
      ts = ts.updated(i, newT)
    }
    (ts.toList, ov)
  }