Hello, I'm a beginer with the preprocessor library. My goal is to generate from a sequence (a)(b)(c) => a::b::c and from (a) => a I have tried with the following code #include <boost/preprocessor/seq/fold_left.hpp> #include <boost/preprocessor/seq/head.hpp> #include <boost/preprocessor/seq/tail.hpp> #define NAME(s, state, x) state::x BOOST_PP_SEQ_FOLD_LEFT(NAME, BOOST_PP_SEQ_HEAD((a)(b)), BOOST_PP_SEQ_TAIL((a)(b))) BOOST_PP_SEQ_FOLD_LEFT(NAME, BOOST_PP_SEQ_HEAD((a)), BOOST_PP_SEQ_TAIL((a))) It works well with sequences with more than 1 element but with a sequence with only an element it fails, having the following preprocessor output (error?) a::b test.cpp:8:1: macro "BOOST_PP_SEQ_ELEM_III" requires 2 arguments, but only 1 given a::BOOST_PP_SEQ_ELEM_III What I'm missing? Thanks in advance, Vicente