public class UnMinus extends UnOp {
  
    public UnMinus (Node child) {
	     super(child);
    }
    public Double eval(Assignation ass) {
	     return - child.eval(ass);
    }
    protected Double compute(Double d) {
       return -d;
    }

    public Node derive(String var) {
	     return new UnMinus(child.derive(var));
    }

}