Simple list zipper

ListZipper.scala

case class ListZipper[T](rev:List[T], fwd:List[T]){
    override def toString = rev.reverse.toString ++" " ++ fwd.toString  
    
    def read:T= fwd.head
    def add(c:T)=ListZipper(rev,c::fwd)
    def update(c:T)=ListZipper(rev,c::fwd.tail)
    def remove()=ListZipper(rev,fwd.tail)  

    def back=ListZipper(rev.tail,rev.head::fwd)
    def forward=ListZipper(fwd.head::rev,fwd.tail)
    
}