Persistent data structures

If every time you want to change something in a data structure, you just go and change it, your code will be full of side-effects. On the other hand, copying complete structures every time is a waste of time and space. There's a middle way, with persistent data structures, which, if handled correctly, let you apply changes while creating new structures, in an efficient way.

Working with lists

Let's consider a simple procedure: suppose you have a list, and you want to add a new element to it. How would you do it? We can assume each node is a NodeList object.

class ListNode {
   constructor(value, next = null) {
       this.value = value;
       this.next = next;
   }
}

A possible list would be...