anchor.diff:     ;
   
   line
  -   : lbl? (assemblerdirective | instruction) comment?
  +   : lbl? (assemblerdirective | instruction)? comment?
      ;
   
   instruction
  -   : opcode? expressionlist?
  +   : opcode expressionlist?
      ;
   
   lbl
  
positive.code:    | name
     | string
     | ('(' expression ')')
     | ((number | name)? '[' expression ']')
     | NOT expression
     ;
  
  dollar
     : DOLLAR
  
negative.code:    : P T R
     ;
  
  REGISTER
     : A X | B X | C X | D X | C I | D I | B P | S P | I P | C S | D S | E S | S S
     ;
  