I am trying to write a parser which skipps white space and C, Java style comments. To get familiar with spirit, I did some experiments, here is a question. First, I write a simple grammar to accept some non-white space chars. //////////////////////////////////////////////////////////////////////////////// struct FOO_GRAMMAR : public grammar<FOO_GRAMMAR> { template <typename ScannerT> struct definition { typedef rule<ScannerT> rule_t; definition(ABNF_GRAMMAR const & self) { r_LETTER = range_p('a','z') | range_p('A','Z') | '.'; r = (+r_LETTER); } rule_t r, r_LETTER; rule_t const& start() const { return r; } }; }; //////////////////////////////////////////////////////////////////////////////// I used FOO_GRAMMAR with space_p as skip parser: ////////////////////////////////////////////////////////////////////////////// FOO_GRAMMAR g; std::string line = "This is a test parser."; parse_info<> info = parse(line.begin(),line.end(), g, space_p); //////////////////////////////////////////////////////////////////////////////// This works perfectly. Then, I tried to wrap the skip parser in a skip grammar, since eventually I need a more complicated parser. So I wrote the skip grammar as: /////////////////////////////////////////////////////////////////////////////// struct SKIP_GRAMMAR : public grammar<SKIP_GRAMMAR> { template <typename ScannerT> struct definition { typedef rule<ScannerT> rule_t; definition(SKIP_GRAMMAR const & self) { rule_t r_SKIP = space_p; } rule_t r_SKIP; rule_t const& start() const { return r_SKIP; } }; }; ///////////////////////////////////////////////////////////////////////// I tried to parse the same sentence as before: /////////////////////////////////////////////////////////////////////////// FOO_GRAMMAR g; SKIP_GRAMMAR skip; std::string line = "This is a test parser."; parse_info<> info = parse(line.begin(),line.end(), g, skip); ////////////////////////////////////////////////////////////////////////// This time the parsing failed. Can anyone tell me why? I thought grammars are just like rules. And any suggestion on building a parser skipping certain pattern? I just can figure it out by reading the doc. Thank you. _________________________________________________________________ Persistent heartburn? Check out Digestive Health & Wellness for information and advice. http://gerd.msn.com/default.asp