Synopsis

template <template <class, ..., class> class T, class P1, ..., class Pn>
struct sequence_applyn;

This is a parser combinator.

Description

It applies the P1 ... Pn parsers on the input in order. When all of them succeed, the result of parsing with sequence_applyn is the T template class instantiated with the results of the P1 ... Pn parsers. When any of the P1 ... Pn parsers reject the input, the error is propagated.

n has to be in the [1..BOOST_METAPARSE_LIMIT_SEQUENCE_SIZE) range.

Header

#include <boost/metaparse/sequence_apply.hpp>

Expression semantics

For any n > 0, p1 ... pn parsers, t template class with n class arguments, s compile-time string and pos source position the following are equivalent:

sequence_apply<t, p1, ..., pn>::apply<s, pos>::type

when sequence<p1, ..., pn> accepts the input:

return_<
  t<
    mpl::at_c<0, get_result<sequence<p1,...,pn>::apply<s, pos>>::type>::type,
    ...
    mpl::at_c<n, get_result<sequence<p1,...,pn>::apply<s, pos>>::type>::type,
  >
>::apply<s, pos>::type

when sequence<p1, ..., pn> rejects the input:

sequence<p1, ..., pn>::apply<s, pos>::type

Example

#include <boost/metaparse/sequence_apply.hpp>
#include <boost/metaparse/int_.hpp>
#include <boost/metaparse/middle_of.hpp>
#include <boost/metaparse/lit_c.hpp>
#include <boost/metaparse/start.hpp>
#include <boost/metaparse/string.hpp>
#include <boost/metaparse/get_result.hpp>

#include <boost/type_traits/is_same.hpp>

using namespace boost::metaparse;

template <int Real, int Imaginary>
struct complex_c { typedef complex_c type; };

template <class Real, class Imaginary>
struct complex : complex_c<Real::type::value, Imaginary::type::value> {};

typedef
  sequence_apply2<complex, int_, middle_of<lit_c<'+'>, int_, lit_c<'i'>>>
  complex_parser;

static_assert(
  boost::is_same<
    complex_c<1, 2>,
    get_result<
      complex_parser::apply<BOOST_METAPARSE_STRING("1+2i"), start>
    >::type::type
  >::type::value,
  "the result of parsing should be the list of digit values"
);