73ef4ff3
 Hu Chunming
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[#iterate]
[section iterate]
[h1 Synopsis]
template <class P, class N>
struct iterate;
This is a [link parser_combinator parser combinator].
[table Arguments
[[Name] [Type]]
[[`P`] [[link parser parser]]]
[[`N`] [[link boxed_value boxed] non-negative integer value]]
]
[h1 Description]
It applies `P` on the input string `N` times. The result of parsing is a
sequence of the results of the individual applications of `P`. `P` has to accept
the input `N` times for `iterate` to accept it.
[h1 Header]
#include <boost/metaparse/iterate.hpp>
[h1 Expression semantics]
For any `p` parser, `n` wrapped integer the following are equivalent:
iterate<p, n>
iterate_c<p, n::type::value>
[h1 Example]
#include <boost/metaparse/iterate.hpp>
#include <boost/metaparse/digit.hpp>
#include <boost/metaparse/string.hpp>
#include <boost/metaparse/start.hpp>
#include <boost/metaparse/get_result.hpp>
#include <boost/metaparse/is_error.hpp>
#include <boost/mpl/vector.hpp>
#include <boost/mpl/equal.hpp>
#include <boost/mpl/char.hpp>
#include <type_traits>
using namespace boost::metaparse;
static_assert(
boost::mpl::equal<
boost::mpl::vector<
boost::mpl::char_<'1'>,
boost::mpl::char_<'2'>,
boost::mpl::char_<'3'>
>,
get_result<
iterate<digit, std::integral_constant<int, 3>>::apply<
BOOST_METAPARSE_STRING("123"),
start
>
>::type
>::type::value,
"the result should be the sequence of the individual applications of digit"
);
static_assert(
boost::mpl::equal<
boost::mpl::vector<
boost::mpl::char_<'1'>,
boost::mpl::char_<'2'>,
boost::mpl::char_<'3'>
>,
get_result<
iterate<digit, std::integral_constant<int, 3>>::apply<
BOOST_METAPARSE_STRING("1234"),
start
>
>::type
>::type::value,
"only three iterations should be made"
);
static_assert(
is_error<
iterate<digit, std::integral_constant<int, 3>>::apply<
BOOST_METAPARSE_STRING("12"),
start
>
>::type::value,
"it should fail when digit can not be applied three times"
);
[endsect]
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