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:       { $parameterList=new ParameterList($LPAREN); }
        (
          ap1=parameterDeclaration 
          { $parameterList.addParameter($ap1.parameter); }
          (
            COMMA 
            ap2=parameterDeclaration
            { $parameterList.addParameter($ap2.parameter); }
          )*
        )? 
        RPAREN
  
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); }
  