anchor.diff:     : DOLLAR
      ;
   
  -register
  +register_
      : REGISTER
      ;
   
  
positive.code:    | NOT expression
     | OFFSET expression
     | LENGTH expression
     | (register ':') expression
     ;
  
  ptr
  
negative.code: argument
     : number
     | dollar
     | register_
     | name
     | string
     | ('(' expression ')')
  