anchor.diff:      ;
   
   term
  -    : identifier
  +    : variable
       | NUMBER
  -    | variable
       | LPAREN expression RPAREN
       ;
   
  
positive.code:     ;
  
  param
      : identifier
      ;
  
  routinebody
  
negative.code:     ;
  
  variable
      : CARAT? DOLLAR? identifier
      ;
  
  set
  