Hi, I am trying to use the preprocessor lib to generate something like Cons<a, Cons<b, Cons<c, Cons<d, Nil> > > > from (a) (b) (c) (d) I tried something like #define START(x) Cons<x,Nil> #define ADD(s,state,x) Cons<x,state > #define GENERATE(x) BOOST_PP_SEQ_FOLD_RIGHT(ADD,START(BOOST_PP_SEQ_HEAD(BOOST_PP_SEQ_REVERSE(x))),BOOST_PP_SEQ_POP_BACK(x)) but immediately got into trouble with the commas. The best I can do is to add parentheses around the content of START and ADD, but that generated (Cons<a, (Cons<b, (Cons<c, (Cons<d, Nil>) >) >) >) which is not valid. Is there any way I can achieve the desired output? Thanks, Di, Yu 10.30 __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com