89 lines
2.0 KiB
Plaintext
89 lines
2.0 KiB
Plaintext
[#repeated]
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[section repeated]
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[h1 Synopsis]
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template <class P>
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struct repeated;
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This is a [link parser_combinator parser combinator].
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[table Arguments
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[[Name] [Type]]
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[[`P`] [[link parser parser]]]
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]
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[h1 Description]
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It applies `P` on the input string repeatedly as long as `P` accepts the input.
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The result of parsing is a sequence of the results of the individual
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applications of `P`.
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When `P` rejects the input for the first time, `repeated` still accepts the
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input and the result of parsing is an empty sequence.
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Here is a diagram showing how `repeated` works by example:
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using int_token = token<int_>;
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[$images/metaparse/repeated_diag1.png [width 70%]]
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Further details can be found in the [link repetition Repetition] section
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of the [link manual User Manual].
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[h1 Header]
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#include <boost/metaparse/repeated.hpp>
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[h1 Expression semantics]
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For any `p` parser the following are equivalent:
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repeated<p>
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foldl<
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p,
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/* unspecified empty sequence */,
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boost::mpl::push_back<_2, _1>
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>
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[h1 Example]
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#include <boost/metaparse/repeated.hpp>
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#include <boost/metaparse/digit_val.hpp>
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#include <boost/metaparse/start.hpp>
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#include <boost/metaparse/string.hpp>
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#include <boost/metaparse/get_result.hpp>
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#include <boost/mpl/equal.hpp>
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#include <boost/mpl/vector.hpp>
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#include <boost/mpl/int.hpp>
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using namespace boost::metaparse;
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using digits = repeated<digit_val>;
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static_assert(
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boost::mpl::equal<
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get_result<digits::apply<BOOST_METAPARSE_STRING("1234"), start>>::type,
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boost::mpl::vector<
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boost::mpl::int_<1>,
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boost::mpl::int_<2>,
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boost::mpl::int_<3>,
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boost::mpl::int_<4>
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>
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>::type::value,
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"the result of parsing should be the list of digit values"
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);
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static_assert(
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boost::mpl::equal<
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get_result<digits::apply<BOOST_METAPARSE_STRING("x"), start>>::type,
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boost::mpl::vector<>
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>::type::value,
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"repeated should accept the input when it can't parse anything with digit_val"
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);
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[endsect]
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