[#digit]
[section digit]

[h1 Synopsis]

  struct digit;

This is a [link parser parser].

[h1 Description]

Parser accepting one character in the range `0-9`. The
result of the parser is the accepted character.

[h1 Header]

  #include <boost/metaparse/digit.hpp>

[h1 Expression semantics]

The following are equivalent:

  digit
  
  accept_when<one_char, util::is_digit, error::digit_expected>

[h1 Example]

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

[endsect]