anchor.diff:      : LPAREN 
         { $positionalArgumentList = new PositionalArgumentList($LPAREN); }
         ( pa1=positionalArgument
  -        { $positionalArgumentList.addPositionalArgument($pa1.positionalArgument); }
  +        { if ($pa1.positionalArgument!=null)
  +              $positionalArgumentList.addPositionalArgument($pa1.positionalArgument); }
           (
             COMMA 
             pa2=positionalArgument
  -          { $positionalArgumentList.addPositionalArgument($pa2.positionalArgument); }
  +          { if ($pa2.positionalArgument!=null)
  +              $positionalArgumentList.addPositionalArgument($pa2.positionalArgument); }
           )* 
           (
             ELLIPSIS
  
positive.code:     : SMALLER_OP
        { $typeParameterList = new TypeParameterList($SMALLER_OP); }
        tp1=typeParameter
        { $typeParameterList.addTypeParameterDeclaration($tp1.typeParameter); }
        (
          COMMA 
          tp2=typeParameter
          { $typeParameterList.addTypeParameterDeclaration($tp2.typeParameter); }
        )*
        LARGER_OP
        { $typeParameterList.setEndToken($LARGER_OP); }
  
negative.code:     : SMALLER_OP
        { $typeArgumentList = new TypeArgumentList($SMALLER_OP); }
        ta1=typeArgument 
        { if ($ta1.type!=null)
              $typeArgumentList.addType($ta1.type); }
        (
          COMMA 
          ta2=typeArgument
          { if ($ta2.type!=null)
              $typeArgumentList.addType($ta2.type); }
        )* 
        LARGER_OP
        { $typeArgumentList.setEndToken($LARGER_OP); }
  