I have been writing a grammar in C++ using Spirit Qi from Boost library. As a novice in the language, it was a tough to get used to the syntax and quirks of the library but now I kind of understand how it works.
I am having an error when using qi::lexeme. My actual grammar is quite big, so I made a small code snippet where the same problem is present. The following code compiles without errors:
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_object.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/fusion/include/boost_tuple.hpp>
#include <set>
#include <iostream>
#include <string>
#include <complex>
namespace client
{
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
typedef boost::tuple<char, char> range;
}
namespace client
{
template <typename Iterator>
struct employee_parser : qi::grammar<Iterator, range(), ascii::space_type>
{
employee_parser() : employee_parser::base_type(start)
{
using qi::lit;
using qi::lexeme;
using ascii::char_;
range_rule =
char_("a-z") >> lit("-") >> char_("a-z")
| char_("A-Z") >> lit("-") >> char_("A-Z")
| char_("0-9") >> lit("-") >> char_("0-9")
;
start = range_rule;
}
qi::rule<Iterator, range(), ascii::space_type> range_rule;
qi::rule<Iterator, range(), ascii::space_type> start;
};
}
int main()
{
typedef std::string::const_iterator iterator_type;
typedef client::employee_parser<iterator_type> employee_parser;
employee_parser g;
return 0;
}
Now, if I replace the line start = range_rule; and use start = lexeme[range_rule]; instead, the compilation fails.
As I read from the docs, lexeme[a] should preserve the subject parser's attributes, so I can't understand why it fails. The output error is huge and pretty cryptic so I don't have any clues:
In file included from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal.hpp:14:0,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi.hpp:21,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/include/qi.hpp:16,
from cpp/tests/test2.cpp:2:
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/rule.hpp: In instantiation of ‘bool boost::spirit::qi::rule<Iterator, T1, T2, T3, T4>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Context = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >; Skipper = boost::spirit::qi::detail::unused_skipper<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> > >; Attribute = boost::tuples::tuple<char, char>; Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; T1 = boost::tuples::tuple<char, char>(); T2 = boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>; T3 = boost::spirit::unused_type; T4 = boost::spirit::unused_type]’:
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/reference.hpp:43:72: required from ‘bool boost::spirit::qi::reference<Subject>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; Context = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >; Skipper = boost::spirit::qi::detail::unused_skipper<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> > >; Attribute = boost::tuples::tuple<char, char>; Subject = const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type>]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/directive/lexeme.hpp:66:64: required from ‘typename boost::disable_if<boost::spirit::qi::detail::is_unused_skipper<Skipper>, bool>::type boost::spirit::qi::lexeme_directive<Subject>::parse(Iterator&, const Iterator&, Context&, const Skipper&, Attribute&) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; Context = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >; Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >; Attribute = boost::tuples::tuple<char, char>; Subject = boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type> >; typename boost::disable_if<boost::spirit::qi::detail::is_unused_skipper<Skipper>, bool>::type = bool]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/detail/parser_binder.hpp:43:54: required from ‘bool boost::spirit::qi::detail::parser_binder<Parser, Auto>::call(Iterator&, const Iterator&, Context&, const Skipper&, mpl_::false_) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >; Context = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >; Parser = boost::spirit::qi::lexeme_directive<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type> > >; Auto = mpl_::bool_<false>; mpl_::false_ = mpl_::bool_<false>]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/detail/parser_binder.hpp:53:24: required from ‘bool boost::spirit::qi::detail::parser_binder<Parser, Auto>::operator()(Iterator&, const Iterator&, Context&, const Skipper&) const [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; Skipper = boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >; Context = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >; Parser
= boost::spirit::qi::lexeme_directive<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type> > >; Auto = mpl_::bool_<false>]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/function_template.hpp:138:22: required from ‘static R boost::detail::function::function_obj_invoker4<FunctionObj, R, T0, T1, T2, T3>::invoke(boost::detail::function::function_buffer&, T0, T1, T2, T3) [with FunctionObj = boost::spirit::qi::detail::parser_binder<boost::spirit::qi::lexeme_directive<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type> > >, mpl_::bool_<false> >; R = bool; T0 = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T1 = const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T2 = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >&; T3 = const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/function_template.hpp:936:38: [ skipping 2 instantiation contexts, use -ftemplate-backtrace-limit=0 to disable ]
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/function_template.hpp:1074:16: required from ‘boost::function<R(T0, T1, T2, T3)>::function(Functor, typename boost::enable_if_c<(! boost::is_integral<Functor>::value), int>::type) [with Functor = boost::spirit::qi::detail::parser_binder<boost::spirit::qi::lexeme_directive<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type> > >, mpl_::bool_<false> >; R = bool; T0 = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T1 = const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T2 = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >&; T3 = const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&; typename boost::enable_if_c<(! boost::is_integral<Functor>::value), int>::type = int]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/function_template.hpp:1127:5: required from ‘typename boost::enable_if_c<(! boost::is_integral<Functor>::value), boost::function<R(T0, T1, T2, T3)>&>::type boost::function<R(T0, T1, T2, T3)>::operator=(Functor) [with Functor = boost::spirit::qi::detail::parser_binder<boost::spirit::qi::lexeme_directive<boost::spirit::qi::reference<const boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type> > >,
mpl_::bool_<false> >; R = bool; T0 = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T1 = const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T2 = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >&; T3 = const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&; typename boost::enable_if_c<(! boost::is_integral<Functor>::value), boost::function<R(T0, T1, T2, T3)>&>::type = boost::function<bool(__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&, const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&, boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >&, const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&)>&]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/rule.hpp:183:19: required from ‘static void boost::spirit::qi::rule<Iterator,
T1, T2, T3, T4>::define(boost::spirit::qi::rule<Iterator, T1, T2, T3, T4>&, const Expr&, mpl_::true_) [with Auto = mpl_::bool_<false>; Expr = boost::proto::exprns_::expr<boost::proto::tagns_::tag::subscript, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::lexeme>, 0>&, boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type>&>, 2>; Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; T1 = boost::tuples::tuple<char, char>(); T2 = boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>; T3 = boost::spirit::unused_type; T4 = boost::spirit::unused_type; mpl_::true_ = mpl_::bool_<true>]’
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/rule.hpp:221:32: required from ‘boost::spirit::qi::rule<Iterator, T1, T2, T3,
T4>& boost::spirit::qi::rule<Iterator, T1, T2, T3, T4>::operator=(const Expr&) [with Expr = boost::proto::exprns_::expr<boost::proto::tagns_::tag::subscript, boost::proto::argsns_::list2<const boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::lexeme>, 0>&, boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type>&>, 2>; Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >; T1 = boost::tuples::tuple<char, char>(); T2 = boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>; T3 = boost::spirit::unused_type; T4 = boost::spirit::unused_type]’
cpp/tests/test2.cpp:40:19: required from ‘client::employee_parser<Iterator>::employee_parser() [with Iterator = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >]’
cpp/tests/test2.cpp:56:21: required from here
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/rule.hpp:304:17: error: no match for call to ‘(const function_type {aka const boost::function<bool(__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&, const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&, boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >&, const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&)>}) (__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&, const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&, boost::spirit::qi::rule<__gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >, boost::tuples::tuple<char, char>(), boost::proto::exprns_::expr<boost::proto::tagns_::tag::terminal, boost::proto::argsns_::term<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >, 0>, boost::spirit::unused_type, boost::spirit::unused_type>::context_type&, const boost::spirit::qi::detail::unused_skipper<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> > >&)’
if (f(first, last, context, skipper))
^~
In file included from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/detail/maybe_include.hpp:43:0,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/detail/function_iterate.hpp:14,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/preprocessor/iteration/detail/iter/forward1.hpp:67,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/function.hpp:70,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal/rule.hpp:16,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi/nonterminal.hpp:14,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/home/qi.hpp:21,
from /home/martin/vscode_cpp_projects/boost_1_68_0/boost/spirit/include/qi.hpp:16,
from cpp/tests/test2.cpp:2:
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/function_template.hpp:763:17: note: candidate: boost::function4<R, T1, T2, T3, T4>::result_type boost::function4<R, T1, T2, T3, T4>::operator()(T0, T1, T2, T3) const [with R = bool; T0 = __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T1 = const __gnu_cxx::__normal_iterator<const char*, std::__cxx11::basic_string<char> >&; T2 = boost::spirit::context<boost::fusion::cons<boost::tuples::tuple<char, char>&, boost::fusion::nil_>, boost::fusion::vector<> >&; T3 = const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&; boost::function4<R, T1, T2, T3, T4>::result_type = bool]
result_type operator()(BOOST_FUNCTION_PARMS) const
^~~~~~~~
/home/martin/vscode_cpp_projects/boost_1_68_0/boost/function/function_template.hpp:763:17: note: no known conversion for argument 4 from ‘const boost::spirit::qi::detail::unused_skipper<boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> > >’ to ‘const boost::spirit::qi::char_class<boost::spirit::tag::char_code<boost::spirit::tag::space, boost::spirit::char_encoding::ascii> >&’
As I read from the docs, lexeme[a] should preserve the subject parser's attributes, so I can't understand why it fails.
Yes it preserves the attributes. It does NOT preserve the skipper (for obvious reasons), and your range_rule declares one. The compiler messages contain this info:
BOOST_STATIC_ASSERT_MSG((is_same<skipper_type, unused_type>::value ||
!is_same<Skipper, unused_type>::value),
"The rule was instantiated with a skipper type but you have not pass any. "
"Did you use `parse` instead of `phrase_parse`?");
So, drop the skipper from the range_rule. Ironically, just dropping it will implicitly make it behave like a lexeme so you wouldn't need the lexeme[] around it anyways.
See also Boost spirit skipper issues
In short:
I usually group my rules to indicate as much, and preface them with a comment, like:
private:
qi::rule<Iterator, range(), ascii::space_type> start;
// lexmes
qi::rule<Iterator, range()> range_rule;
But I also usually encapsulate the skipper unless it really makes sense (?!) for the caller to change the skipper.
See also similar tasks:
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_object.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/fusion/include/boost_tuple.hpp>
#include <set>
#include <iostream>
#include <string>
#include <complex>
namespace client
{
namespace qi = boost::spirit::qi;
typedef boost::tuple<char, char> range;
}
namespace client
{
template <typename Iterator>
struct employee_parser : qi::grammar<Iterator, range()>
{
employee_parser() : employee_parser::base_type(start)
{
using qi::lit;
using qi::lexeme;
using qi::ascii::char_;
range_rule =
char_("a-z") >> lit("-") >> char_("a-z")
| char_("A-Z") >> lit("-") >> char_("A-Z")
| char_("0-9") >> lit("-") >> char_("0-9")
;
start = qi::skip(qi::ascii::space) [ range_rule ];
}
private:
qi::rule<Iterator, range()> start;
// lexmes
qi::rule<Iterator, range()> range_rule;
};
}
int main()
{
typedef std::string::const_iterator iterator_type;
typedef client::employee_parser<iterator_type> employee_parser;
employee_parser g;
std::string const input("a-k");
client::range r;
return parse(begin(input), end(input), g, r)
? 0
: 1;
}