Basic Abstract Syntax Tree Node

Node.kt

open class Node {
  
  private var children: MutableCollection<Node>? = null
  
  fun getChildren(): Collection<Node>? = children
  
  fun hasChildren(): Boolean = children?.isNotEmpty() == true
  
  fun addChild(child: Node) {
    children = (children ?: ArrayList()).apply {
      add(child)
    }
  }
}