[boost] Preprocessor directive for a sequence that differs only in datatype

Hello Everyone, I was trying to use the boost.preprocessor to write some code which otherwise needs to be written for all the cases. Here's the code: https://github.com/BoostGSoC17/dataframe/blob/master/include/df.cpp (line no. 430 and 431). But on compilation it gives the error: error: macro "BOOST_PP_SEQ_ELEM_III" requires 2 arguments, but only 1 given print_column (i); I didn't understand the reason as when I wrote: print_column (i); it works fine. Can anyone help me understand the error or provide an alternative way to do the same thing? Thanks in advance, Best Regards, Rishabh