anchor.diff:  argument
      : number
      | dollar
  +   | ques
      | register
      | name
      | string
  
positive.code: |X O R
     ;
  
  
  DOLLAR
     : '$'
     ;
  
  
  SIGN
     : '+' | '-'
  
negative.code:    : SIGN? NUMBER
     ;
  
  /* not sure what JMPS is */
  opcode
     : OPCODE | 'JMPS'
     ;
  
  comment
  