71 lines
1.5 KiB
Plaintext
71 lines
1.5 KiB
Plaintext
[#first_of]
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[section first_of]
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[h1 Synopsis]
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template <class... Ps>
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struct first_of;
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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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[[`Ps`] [[link parser parser]s]]
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]
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[h1 Description]
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`first_of` applies the `Ps...` parsers in sequence. It accepts an input when all
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parsers accept it. The result of parsing is the result of the first parser.
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On compilers, which are not C++11-compliant, the maximum number of parsers
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`first_of` accepts can be specified with the
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`BOOST_METAPARSE_LIMIT_SEQUENCE_SIZE` macro. Its default value is `5`.
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[h1 Header]
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#include <boost/metaparse/first_of.hpp>
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[h1 Expression semantics]
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For any `p1`, ... `pn` parsers
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first_of<p1, ..., pn>
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is equivalent to
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nth_of_c<0, p1, ..., pn>
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[h1 Example]
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#include <boost/metaparse/first_of.hpp>
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#include <boost/metaparse/int_.hpp>
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#include <boost/metaparse/lit_c.hpp>
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#include <boost/metaparse/string.hpp>
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#include <boost/metaparse/start.hpp>
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#include <boost/metaparse/is_error.hpp>
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#include <boost/metaparse/get_result.hpp>
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#include <type_traits>
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using namespace boost::metaparse;
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using int_with_semicolon = first_of<int_, lit_c<';'>>;
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static_assert(
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is_error<
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int_with_semicolon::apply<BOOST_METAPARSE_STRING("13"), start>
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>::type::value,
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"int without semicolon is rejected"
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);
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static_assert(
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get_result<
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int_with_semicolon::apply<BOOST_METAPARSE_STRING("13;"), start>
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>::type::value,
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"the result is the result of the first parser"
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);
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[endsect]
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