ArrayUpdateNode.java

import java.util.List;

public class ArrayUpdateNode extends Node
{
    private Node array;
    private Node indexExpression;
    private Node rightSideExpression;
    
    public ArrayUpdateNode(Node array, Node indexExpression,
                            Node rightSideExpression)
    {
        this.array = array;
        this.indexExpression = indexExpression;
        this.rightSideExpression = rightSideExpression;
    }
    
    public int ToInt(Node node)
    {
        Object res = node.eval();
        return ((Integer) res).intValue();
    }
    
    public Object eval()
    {        
        Object arrayVariable = array.eval();
        int index = ToInt(indexExpression);
        Object newValue = rightSideExpression.eval();
        
        Object ret = ((List) arrayVariable).set(index, newValue);
        
        return ret;
    }
}