anchor.diff:  
   OF
       :   'of'
  +    ;
  +
  +OUT
  +    :   'out'
       ;
   
   SUBTYPE
  
positive.code: 
  enumeration
      : '{' expressions '}'
      -> ^(ENUM_LIST expressions?)
      ;
      
  primary
  
negative.code:     ;
  
  variance
      : 'in' -> IN | 'out' -> OUT
      ;
      
  dimensionalTypeParameter
  