final case class Triple (posOdd: List[Int], posEven: List[Int], neg: List[Int])

def triple(xs: List[Int]): Triple =
   xs.foldLeft(Triple(Nil, Nil, Nil))(
     (acc, x) => 
        if (x < 0) 
          acc.copy(neg = x::acc.neg)
        else if (x % 2 == 0)
          acc.copy(posEven = x::acc.posEven)
        else
          acc.copy(posOdd = x::acc.posOdd)
     )

triple(List(2, 0, -1 , 3, 5 , -2))