CODEWITHSUNDEEP
scalafunctional-programming
Jack Widman
Jack Widman

Reputation: 11

How to write the following Scala code without vars

What follows is a simple snippet of code defining a Node class for representing linked lists and a method for adding a node to the end of a list. In the code, there are two vars. How can I write this code without any vars?

case class Node[A](data: A, var next: Option[Node[A]])

def addNodeToEnd[A](node: Node[A], nodeToAdd: Node[A]): Node[A] = {
    if (node.next == None) {
        node.next = Some(nodeToAdd)
    } else {
        var current = node
        while ( current.next != None) {
           current = current.next.getOrElse(current)
        }
        current.next = Some(nodeToAdd)      
    }
    node
}

//Test                              
val node = Node(1, Some(Node(2, Some(Node(3, None)))))
val nodeToAdd = Node(88, None)

println(addNodeToEnd(node, nodeToAdd))

Upvotes: 1

Views: 123

Answers (1)

jwvh
jwvh

Reputation: 51271

Here's one approach. No vars. No mutation.

case class Node[A](data: A, next: Option[Node[A]])

def addToEnd[A](node: Node[A], toAdd: A): Node[A] =
  node.next.fold(node.copy(next = Some(Node(toAdd,None))))(
            n => node.copy(next = Some(addToEnd(n,toAdd))))

//Test                              
val list = Node(1, Some(Node(2, Some(Node(3, None)))))
addToEnd(list, 88)
//res0: Node[Int] = Node(1,Some(Node(2,Some(Node(3,Some(Node(88,None)))))))

Or, if you prefer...

def nodeAppend[A](ns: Node[A], toAppnd: Node[A]): Node[A] =
  ns.next.fold(ns.copy(next = Some(toAppnd)))(
        nxt => ns.copy(next = Some(nodeAppend(nxt, toAppnd))))
//Test                              
val list = Node(1, Some(Node(2, None)))
val listToAdd = Node(88, Some(Node(99,None)))

nodeAppend(list, listToAdd)
//res0: Node[Int] = Node(1,Some(Node(2,Some(Node(88,Some(Node(99,None)))))))

Upvotes: 1

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