repeated.qbk
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[#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]