Implement enclosed assign.
Refactoring. Move createDataframe related method from QList to QFunction.
Refactoring extract createDataFrame related code to DataFrameBuilder.
Support named arg for data.frame().
Support multi dim subscript (didn't yet?) like m[1, 2].
Implement rbind.
Handle for invalid last column.
Support subscript by col, multi col name (like df[, c("hoge", "ika")]).