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