import std/lists
import std/options

proc snipAndReplace[T](front, back: Option[var DoublyLinkedNode[T]], x: T) =
  var node = newDoublyLinkedNode(x)
  if front.isSome:
    front.get.next = node
    node.prev = front.get
  if back.isSome:
    back.get.prev = node
    node.next = back.get

var lst = initDoublyLinkedList[int]()
lst.add 1
lst.add 6
lst.add 3

echo lst
snipAndReplace(some(lst.head), some(lst.tail), 2)
echo lst