Hi all, i would like to implement a grammar that transform a*(b+c) to a*b+a*c where a,b and c are terminals. The implementation of this grammar is straightforward and should compile. However i got errors that i dont understand. Below is the code that reproduces the errors. Thanks for any help, Kim # include # include # include # include # include # define PRECISION_MAKE_tag(name) \ struct name \ { \ friend std::ostream& operator<< (std::ostream& s, name const&) \ { \ return s<< #name; \ } \ }; # define PRECISION_MAKE_terminal(name) \ proto::terminal< tag::name >::type const name = {{}} namespace proto = boost::proto; namespace tag{ PRECISION_MAKE_tag(a); PRECISION_MAKE_tag(b); PRECISION_MAKE_tag(c); } namespace mpl = boost::mpl; namespace fusion = boost::fusion; using proto::_; struct DistributiveLaw : proto::or_< proto::when< proto::multiplies< proto::terminal< _ > , proto::plus< _, _ > > , proto::plus< proto::multipliesproto::_left,proto::_left(proto::_right) , proto::multipliesproto::_left,proto::_right(proto::_right) //, proto::_right(proto::_right) >( proto::multipliesproto::_left,proto::_left(proto::_right) (proto::_left,proto::_left(proto::_right)) , proto::multipliesproto::_left,proto::_right(proto::_right) (proto::_left,proto::_right(proto::_right)) //, proto::_right(proto::_right) ) > , proto::otherwise > > {}; PRECISION_MAKE_terminal(a); PRECISION_MAKE_terminal(b); PRECISION_MAKE_terminal(c); # undef PRECISION_MAKE_tag # undef PRECISION_MAKE_terminal int main() { proto::display_expr(a*(b+c)); proto::display_expr(DistributiveLaw()( a*(b+c) )); return boost::exit_success; }