The following trivial program fails to compile: #include <boost/phoenix/core/limits.hpp> #include <boost/numeric/conversion/converter.hpp> It generates the following: In file included from ../../../../branches/release/boost/numeric/conversion/detail/is_subranged.hpp:17, from ../../../../branches/release/boost/numeric/conversion/detail/conversion_traits.hpp:21, from ../../../../branches/release/boost/numeric/conversion/conversion_traits.hpp:13, from ../../../../branches/release/boost/numeric/conversion/converter.hpp:13, from main.cpp:2: ../../../../branches/release/boost/mpl/multiplies.hpp:38: error: wrong number of template arguments (12, should be 5) ../../../../branches/release/boost/mpl/aux_/preprocessed/gcc/times.hpp:68: error: provided for ‘temp late<class N1, class N2, class N3, class N4, class N5> struct boost::mpl::times’ Phoenix is changing the following fundamental constants: BOOST_PROTO_MAX_ARITY BOOST_MPL_LIMIT_METAFUNCTION_ARITY BOOST_PROTO_MAX_LOGICAL_ARITY BOOST_RESULT_OF_NUM_ARGS IMO, Phoenix shouldn't be touching these. It should work as best it can with the default values. Users who are so inclined can change them. -- Eric Niebler BoostPro Consulting www.boostpro.com