bump version to 12.2.2-pve1

[ceph.git] / ceph / src / boost / libs / metaparse / doc / repeated.qbk

[#repeated]
[section repeated]

[h1 Synopsis]

  template <class P>
  struct repeated;

This is a [link parser_combinator parser combinator].

[table Arguments
  [[Name] [Type]]
  [[`P`]  [[link parser parser]]]
]

[h1 Description]

It applies `P` on the input string repeatedly as long as `P` accepts the input.
The result of parsing is a sequence of the results of the individual
applications of `P`.

When `P` rejects the input for the first time, `repeated` still accepts the
input and the result of parsing is an empty sequence.

Here is a diagram showing how `repeated` works by example:

  using int_token = token<int_>;

[$images/metaparse/repeated_diag1.png [width 70%]]

Further details can be found in the [link repetition Repetition] section
of the [link manual User Manual].

[h1 Header]

  #include <boost/metaparse/repeated.hpp>

[h1 Expression semantics]

For any `p` parser the following are equivalent:

  repeated<p>
  
  foldl<
    p,
    /* unspecified empty sequence */,
    boost::mpl::push_back<_2, _1>
  >

[h1 Example]

  #include <boost/metaparse/repeated.hpp>
  #include <boost/metaparse/digit_val.hpp>
  #include <boost/metaparse/start.hpp>
  #include <boost/metaparse/string.hpp>
  #include <boost/metaparse/get_result.hpp>
  
  #include <boost/mpl/equal.hpp>
  #include <boost/mpl/vector.hpp>
  #include <boost/mpl/int.hpp>
  
  using namespace boost::metaparse;
  
  using digits = repeated<digit_val>;
  
  static_assert(
    boost::mpl::equal<
      get_result<digits::apply<BOOST_METAPARSE_STRING("1234"), start>>::type,
      boost::mpl::vector<
        boost::mpl::int_<1>,
        boost::mpl::int_<2>,
        boost::mpl::int_<3>,
        boost::mpl::int_<4>
      >
    >::type::value,
    "the result of parsing should be the list of digit values"
  );
  
  static_assert(
    boost::mpl::equal<
      get_result<digits::apply<BOOST_METAPARSE_STRING("x"), start>>::type,
      boost::mpl::vector<>
    >::type::value,
    "repeated should accept the input when it can't parse anything with digit_val"
  );

[endsect]