code: private PExp addIs(PExp exp, PType type)
  	{
  		AIsExp isExp = new AIsExp();
  		isExp.setBasicType(type);
  		isExp.setType(new ABooleanBasicType());
  		isExp.setTest(exp.clone());
  		return isExp;
  	}
docs: Just produce one is_(<expression>, <type>) node.