LookupNode.java

import java.util.List;

public class LookupNode extends Node
{
    private VariableNode varNode;
    private Node keyNode;

    public LookupNode(VariableNode varNode, Node keyNode)
    {
        this.varNode = varNode;
        this.keyNode = keyNode;
    }
    
    public Object eval()
    {
        Object var = varNode.eval();
        int index = ((Integer) keyNode.eval()).intValue();        
        Object ret = ((List) var).get(index);        
        return ret;
    }
}