[#keyword]
[section keyword]

[h1 Synopsis]

  template <class S, class ResultType = /* unspecified */>
  struct keyword;

This is a [link parser parser].

[table Arguments
  [[Name]         [Type]]
  [[`S`]          [[link string string]]]
  [[`ResultType`] [[link metaprogramming_value template metaprogramming value]]]
]

[h1 Description]

Parser accepting the keyword `S`. The result of parsing is `ResultType`, which
is optional; when not given, the result of successful parsing is undefined.

[h1 Header]

  #include <boost/metaparse/keyword.hpp>

[h1 Expression semantics]

For any `r` class and `s` compile-time string that is built from the characters
`c1` ... `cn` the following are equivalent:

  keyword<s, r>
  
  last_of<lit<c1>, /* ... */, lit<cn>, return_<r>>

[h1 Example]

  #include <boost/metaparse/keyword.hpp>
  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/start.hpp>
  #include <boost/metaparse/get_result.hpp>
  #include <boost/metaparse/is_error.hpp>
  
  #include <type_traits>
  
  using namespace boost::metaparse;
  
  static_assert(
    get_result<
      keyword<BOOST_METAPARSE_STRING("for"), std::integral_constant<int, 13>>
        ::apply<BOOST_METAPARSE_STRING("for"), start>
    >::type::value == 13,
    "the result of parsing the keyword is keyword's second argument"
  );
  
  static_assert(
    is_error<
      keyword<BOOST_METAPARSE_STRING("for"), std::integral_constant<int, 13>>
        ::apply<BOOST_METAPARSE_STRING("if"), start>
    >::type::value,
    "a word other than the keyword is an error"
  );

[endsect]