@Test
public void grouping() throws Exception {

  Expression expression = parseExpression("-5 add 5");
  assertEquals("{-5 ADD 5}", expression.toString());
  expression = parseExpression("-(5 add 5)");
  assertEquals("{MINUS {5 ADD 5}}", expression.toString());
  
  expression = parseExpression("-( 5 add 5\t)");
  assertEquals("{MINUS {5 ADD 5}}", expression.toString());
  
}