ceph/src/boost/libs/metaparse/doc/repeated.qbk

   1 [#repeated]
   2 [section repeated]
   3
   4 [h1 Synopsis]
   5
   6   template <class P>
   7   struct repeated;
   8
   9 This is a [link parser_combinator parser combinator].
  10
  11 [table Arguments
  12   [[Name] [Type]]
  13   [[`P`]  [[link parser parser]]]
  14 ]
  15
  16 [h1 Description]
  17
  18 It applies `P` on the input string repeatedly as long as `P` accepts the input.
  19 The result of parsing is a sequence of the results of the individual
  20 applications of `P`.
  21
  22 When `P` rejects the input for the first time, `repeated` still accepts the
  23 input and the result of parsing is an empty sequence.
  24
  25 Here is a diagram showing how `repeated` works by example:
  26
  27   using int_token = token<int_>;
  28
  29 [$images/metaparse/repeated_diag1.png [width 70%]]
  30
  31 Further details can be found in the [link repetition Repetition] section
  32 of the [link manual User Manual].
  33
  34 [h1 Header]
  35
  36   #include <boost/metaparse/repeated.hpp>
  37
  38 [h1 Expression semantics]
  39
  40 For any `p` parser the following are equivalent:
  41
  42   repeated<p>
  43
  44   foldl<
  45     p,
  46     /* unspecified empty sequence */,
  47     boost::mpl::push_back<_2, _1>
  48   >
  49
  50 [h1 Example]
  51
  52   #include <boost/metaparse/repeated.hpp>
  53   #include <boost/metaparse/digit_val.hpp>
  54   #include <boost/metaparse/start.hpp>
  55   #include <boost/metaparse/string.hpp>
  56   #include <boost/metaparse/get_result.hpp>
  57
  58   #include <boost/mpl/equal.hpp>
  59   #include <boost/mpl/vector.hpp>
  60   #include <boost/mpl/int.hpp>
  61
  62   using namespace boost::metaparse;
  63
  64   using digits = repeated<digit_val>;
  65
  66   static_assert(
  67     boost::mpl::equal<
  68       get_result<digits::apply<BOOST_METAPARSE_STRING("1234"), start>>::type,
  69       boost::mpl::vector<
  70         boost::mpl::int_<1>,
  71         boost::mpl::int_<2>,
  72         boost::mpl::int_<3>,
  73         boost::mpl::int_<4>
  74       >
  75     >::type::value,
  76     "the result of parsing should be the list of digit values"
  77   );
  78
  79   static_assert(
  80     boost::mpl::equal<
  81       get_result<digits::apply<BOOST_METAPARSE_STRING("x"), start>>::type,
  82       boost::mpl::vector<>
  83     >::type::value,
  84     "repeated should accept the input when it can't parse anything with digit_val"
  85   );
  86
  87 [endsect]
  88