Using BOOST_PP_IDENTITY makes code clearer.

include/boost/preprocessor/facilities/is_empty.hpp

@@ -24,7 +24,7 @@
 # include <boost/preprocessor/config/config.hpp>
 # if ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MSVC() && ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MWCC()
 # include <boost/preprocessor/tuple/elem.hpp>
-# include <boost/preprocessor/facilities/empty.hpp>
+# include <boost/preprocessor/facilities/identity.hpp>
 # else
 # include <boost/preprocessor/cat.hpp>
 # include <boost/preprocessor/detail/split.hpp>
@@ -35,7 +35,7 @@
 # if ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MSVC() && ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MWCC()
 #    define BOOST_PP_IS_EMPTY(x) BOOST_PP_IS_EMPTY_I(x BOOST_PP_IS_EMPTY_HELPER)
 #    define BOOST_PP_IS_EMPTY_I(contents) BOOST_PP_TUPLE_ELEM(2, 1, (BOOST_PP_IS_EMPTY_DEF_ ## contents()))
-#    define BOOST_PP_IS_EMPTY_DEF_BOOST_PP_IS_EMPTY_HELPER 1, 1 BOOST_PP_EMPTY
+#    define BOOST_PP_IS_EMPTY_DEF_BOOST_PP_IS_EMPTY_HELPER 1, BOOST_PP_IDENTITY(1)
 #    define BOOST_PP_IS_EMPTY_HELPER() , 0
 # else
 #    if BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_MSVC()

include/boost/preprocessor/facilities/is_empty_or_1.hpp

@@ -14,6 +14,7 @@
 #
 # include <boost/preprocessor/control/iif.hpp>
 # include <boost/preprocessor/facilities/empty.hpp>
+# include <boost/preprocessor/facilities/identity.hpp>
 # include <boost/preprocessor/facilities/is_1.hpp>
 # include <boost/preprocessor/facilities/is_empty.hpp>
 #
@@ -22,7 +23,7 @@
 # define BOOST_PP_IS_EMPTY_OR_1(x) \
     BOOST_PP_IIF( \
         BOOST_PP_IS_EMPTY(x BOOST_PP_EMPTY()), \
-        1 BOOST_PP_EMPTY, \
+        BOOST_PP_IDENTITY(1), \
         BOOST_PP_IS_1 \
     )(x) \
     /**/

include/boost/preprocessor/seq/rest_n.hpp

@@ -14,17 +14,17 @@
 #
 # include <boost/preprocessor/arithmetic/inc.hpp>
 # include <boost/preprocessor/config/config.hpp>
-# include <boost/preprocessor/facilities/empty.hpp>
+# include <boost/preprocessor/facilities/identity.hpp>
 # include <boost/preprocessor/seq/detail/split.hpp>
 # include <boost/preprocessor/tuple/elem.hpp>
 #
 # /* BOOST_PP_SEQ_REST_N */
 #
 # if ~BOOST_PP_CONFIG_FLAGS() & BOOST_PP_CONFIG_EDG()
-#    define BOOST_PP_SEQ_REST_N(n, seq) BOOST_PP_TUPLE_ELEM(2, 1, BOOST_PP_SEQ_SPLIT(BOOST_PP_INC(n), (nil) seq BOOST_PP_EMPTY))()
+#    define BOOST_PP_SEQ_REST_N(n, seq) BOOST_PP_TUPLE_ELEM(2, 1, BOOST_PP_SEQ_SPLIT(BOOST_PP_INC(n), BOOST_PP_IDENTITY( (nil) seq )))()
 # else
 #    define BOOST_PP_SEQ_REST_N(n, seq) BOOST_PP_SEQ_REST_N_I(n, seq)
-#    define BOOST_PP_SEQ_REST_N_I(n, seq) BOOST_PP_TUPLE_ELEM(2, 1, BOOST_PP_SEQ_SPLIT(BOOST_PP_INC(n), (nil) seq BOOST_PP_EMPTY))()
+#    define BOOST_PP_SEQ_REST_N_I(n, seq) BOOST_PP_TUPLE_ELEM(2, 1, BOOST_PP_SEQ_SPLIT(BOOST_PP_INC(n), BOOST_PP_IDENTITY( (nil) seq )))()
 # endif
 #
 # endif