```int eval(Node n) { switch(n) { case...

# announcements

[jacob]

int eval(Node n) {
    switch(n) {
        case IntNode(int i): return i;
        case NegNode(Node n): return -eval(n);
        case AddNode(Node left, Node right): return eval(left) + eval(right);
        case MulNode(Node left, Node right): return eval(left) * eval(right);
        default: throw new IllegalStateException(n);
    };
}