anchor.diff:     ;
   
   directive
  -   : argument? assemblerdirective expressionlist
  +   : argument? assemblerdirective expressionlist?
      ;
   
   assemblerdirective
  
positive.code:    | name 
     | string
     | ('(' expression ')')
     ;
  
  dollar
  
negative.code: 
  
  NUMBER
     : '$'? ('-')? [0-9a-fA-F] + ('H' | 'h')?
     ;
  
  
  