Insert node at beginning of doubly linked list in swift

Swift program for Insert node at beginning of doubly linked list. Here problem description and explanation.

import Foundation
// Swift 4 Program For
// insert new node at beginning of doubly linked list

// Define class of linked list Node
class LinkNode
{
	var data: Int;
	var next: LinkNode? ;
	var prev: LinkNode? ;
	init(_ data: Int)
	{
		self.data = data;
		self.next = nil;
		self.prev = nil;
	}
}
class DoublyLinkedList
{
	var head: LinkNode? ;
	init()
	{
		self.head = nil;
	}
	// Insert new node at beginning position
	func insert(_ value: Int)
	{
		// Create a node
		let node: LinkNode? = LinkNode(value);
		node!.next = self.head;
		// When linked list is not empty
		if (self.head  != nil)
		{
			self.head!.prev = node;
		}
		// Make new head
		self.head = node;
	}
	// Display node element of doubly linked list
	func display()
	{
		if (self.head == nil)
		{
			print("Empty Linked List");
		}
		else
		{
			print("Doubly Linked List Element :");
			// Get first node of linked list
			var temp: LinkNode? = self.head;
			// iterate linked list 
			while (temp  != nil)
			{
				// Display node value
				print(temp!.data, terminator: "  ");
				// Visit to next node
				temp = temp!.next;
			}
		}
	}
	static func main(_ args: [String])
	{
		let dll: DoublyLinkedList? = DoublyLinkedList();
		// Insert following linked list nodes
		dll!.insert(70);
		dll!.insert(60);
		dll!.insert(50);
		dll!.insert(40);
		dll!.insert(30);
		dll!.insert(20);
		dll!.insert(10);
		//  NULL <- 10 <--> 20 <--> 30 <--> 40 <--> 50 <--> 60 <--> 70->NULL
		dll!.display();
	}
}
DoublyLinkedList.main([String]());

Output

Doubly Linked List Element :
10  20  30  40  50  60  70