anchor.diff:      ;
   
   exclusiveOrExpression returns [Expression element]
  +@after{check_null(retval.element);}
       :   ex=andExpression {retval.element = ex.element;} ( '^' exx=andExpression
       {
            retval.element = new InfixOperatorInvocation("^", retval.element);
  
positive.code:     ;
      
  expression returns [Expression element]
      :   ex=conditionalExpression {retval.element=ex.element;} (op=assignmentOperator exx=expression 
          {String txt = $op.text; 
           if(txt.equals("=")) {
  
negative.code:     ;
  
  inclusiveOrExpression returns [Expression element]
  @after{check_null(retval.element);}
      :   ex=exclusiveOrExpression {retval.element = ex.element;} ( '|' exx=exclusiveOrExpression 
         {
           retval.element = new InfixOperatorInvocation("|", retval.element);
  