Hi, I defined a macro using Boost.Preprocessor that compiles and works fine under gcc but fails to compile under Clang. The macro is defined here: https://github.com/ptal/Boost.Expected/blob/master/include/boost/functional/... And the error message follows this message, the file using the macro is https://github.com/ptal/Boost.Expected/blob/master/example/monadic_calculato... Thanks for any helps, Pierre Talbot Boost.Expected/example/monadic_calculator$ b2 ...patience... ...found 1246 targets... ...updating 2 targets... clang-linux.compile.c++.without-pth bin/clang-linux-3.5.0/debug/monadic_calculator.o monadic_calculator.cpp:141:15: error: use of undeclared identifier 'BOOST_PP_IIF_0' etokens = DO( ^ ../../include/boost/functional/do_yield.hpp:100:17: note: expanded from macro 'DO' #define DO(...) DO_SEQ(BOOST_PP_VARIADIC_TO_SEQ(__VA_ARGS__)) ^ ../../include/boost/functional/do_yield.hpp:97:3: note: expanded from macro 'DO_SEQ' BOOST_PP_SEQ_FOR_EACH_I(DO_ELEM, seq, seq) \ ^ /usr/local/boost_1_55_0/boost/preprocessor/seq/for_each_i.hpp:27:55: note: expanded from macro 'BOOST_PP_SEQ_FOR_EACH_I' # define BOOST_PP_SEQ_FOR_EACH_I(macro, data, seq) BOOST_PP_FOR((macro, data, seq (nil), 0), BOOST_PP_SEQ_FOR_EACH_I_P, BOOST_PP_SEQ_FOR_EACH_I_O, BOOST_PP_SEQ_FOR_EACH_I_M) ^ /usr/local/boost_1_55_0/boost/preprocessor/repetition/for.hpp:27:23: note: expanded from macro 'BOOST_PP_FOR' # define BOOST_PP_FOR BOOST_PP_CAT(BOOST_PP_FOR_, BOOST_PP_AUTO_REC(BOOST_PP_FOR_P, 256)) ^ /usr/local/boost_1_55_0/boost/preprocessor/cat.hpp:22:32: note: expanded from macro 'BOOST_PP_CAT' # define BOOST_PP_CAT(a, b) BOOST_PP_CAT_I(a, b) ^ /usr/local/boost_1_55_0/boost/preprocessor/cat.hpp:29:34: note: expanded from macro 'BOOST_PP_CAT_I' # define BOOST_PP_CAT_I(a, b) a ## b ^ <scratch space>:130:1: note: expanded from here BOOST_PP_FOR_1 ^ /usr/local/boost_1_55_0/boost/preprocessor/repetition/detail/for.hpp:22:37: note: expanded from macro 'BOOST_PP_FOR_1' # define BOOST_PP_FOR_1(s, p, o, m) BOOST_PP_FOR_1_C(BOOST_PP_BOOL(p(2, s)), s, p, o, m) ^ /usr/local/boost_1_55_0/boost/preprocessor/repetition/detail/for.hpp:279:42: note: expanded from macro 'BOOST_PP_FOR_1_C' # define BOOST_PP_FOR_1_C(c, s, p, o, m) BOOST_PP_IIF(c, m, BOOST_PP_TUPLE_EAT_2)(2, s) BOOST_PP_IIF(c, BOOST_PP_FOR_2, BOOST_PP_TUPLE_EAT_4)(BOOST_PP_EXPR_IIF(c, o)(2, s), p, o, m) ^ /usr/local/boost_1_55_0/boost/preprocessor/control/iif.hpp:18:37: note: expanded from macro 'BOOST_PP_IIF' # define BOOST_PP_IIF(bit, t, f) BOOST_PP_IIF_I(bit, t, f) ^ /usr/local/boost_1_55_0/boost/preprocessor/control/iif.hpp:25:39: note: expanded from macro 'BOOST_PP_IIF_I' # define BOOST_PP_IIF_I(bit, t, f) BOOST_PP_IIF_ ## bit(t, f) ^ <scratch space>:136:1: note: expanded from here BOOST_PP_IIF_0 ^