[#alphanum]
[section alphanum]

[h1 Synopsis]

  struct alphanum;

This is a [link parser parser].

[h1 Description]

It accepts one character in the range `a-z`, `A-Z` or `0-9`. The
result of the parser is the accepted character.

[h1 Header]

  #include <boost/metaparse/alphanum.hpp>

[h1 Expression semantics]

The following are equivalent:

  alphanum
  
  one_of<digit, letter>

[h1 Example]

  #include <boost/metaparse/alphanum.hpp>
  #include <boost/metaparse/start.hpp>
  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/is_error.hpp>
  #include <boost/metaparse/get_result.hpp>
  
  using namespace boost::metaparse;
  
  static_assert(
    !is_error<alphanum::apply<BOOST_METAPARSE_STRING("0"), start>>::type::value,
    "alphanum should accept a digit"
  );
  
  static_assert(
    !is_error<alphanum::apply<BOOST_METAPARSE_STRING("x"), start>>::type::value,
    "alphanum should accept a character"
  );
  
  static_assert(
    get_result<
      alphanum::apply<BOOST_METAPARSE_STRING("x"), start>
    >::type::value == 'x',
    "the result of parsing should be the character value"
  );
  
  static_assert(
    is_error<alphanum::apply<BOOST_METAPARSE_STRING(","), start>>::type::value,
    "alphanum should reject a comma"
  );

[endsect]