I've written an implementation of BOOST_PP_IS_UNARY which works for Borland, and hopefully any other preprocessors which the current implementation doesn't. It is: #define EAT2(x,y) #define IS_UNARY_CHECK(x) ~, 1 BOOST_PP_RPAREN() \ EAT2 BOOST_PP_LPAREN() ~ #define IS_UNARY(x) IS_UNARY_1(IS_UNARY_CHECK x, 0) #define IS_UNARY_1(x, y) IS_UNARY_2(x, y) #define IS_UNARY_2(x, y) y For a non-unary argument, the expansion is simple: IS_UNARY(x) => IS_UNARY_1(IS_UNARY_CHECK x, 0) => IS_UNARY_2(IS_UNARY_CHECK x, 0) => 0 For a unary argument, it expands like this (I might have got the expansion order slightly wrong but, hopefully, this illustrates how it works): IS_UNARY((x)y) => IS_UNARY_1(IS_UNARY_CHECK(x)y), 0) => IS_UNARY_2(~, 1 BOOST_PP_RPAREN() EAT2 BOOST_PP_LPAREN() ~y, 0) => IS_UNARY_2(~, 1) EAT2(~y, 0) => 1 The same technique can be used for BOOST_PP_IS_NULLARY and BOOST_PP_IS_BINARY. So, if this is used as for borland, could these marcros be made 'public'? Also, with a full working BOOST_PP_IS_UNARY, I think it should be possible to make BOOST_PP_SEQ_NIL act as an empty sequence, if I write a patch to do that would it be accepted? Daniel