102 lines
3.2 KiB
Plaintext
102 lines
3.2 KiB
Plaintext
[#foldl_reject_incomplete_start_with_parser]
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[section foldl_reject_incomplete_start_with_parser]
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[h1 Synopsis]
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template <class P, class StateP, class ForwardOp>
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struct foldl_reject_incomplete_start_with_parser;
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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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[[`StateP`] [[link parser parser]]]
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[[`ForwardOp`] [[link metafunction_class template metafunction class] taking two arguments]]
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]
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[h1 Description]
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The same as [link foldl_start_with_parser `foldl_start_with_parser`], but once
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`P` rejects the input, `foldl_reject_incomplete_start_with_parser` checks if `P`
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consumes any characters before rejecting the input. If so,
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`foldl_reject_incomplete_start_with_parser` rejects the input with the same
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error message this last application of `P` returned. Otherwise
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`foldl_reject_incomplete_start_with_parser` accepts the input and gives the same
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result as [link foldl_start_with_parser `foldl_start_with_parser`].
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Here is a diagram showing how `foldl_reject_incomplete_start_with_parser` works
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by example:
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using int_token = token<int_>;
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using plus_token = token<lit_c<'+'>>;
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using plus_int = last_of<plus_token, int_token>;
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using sum_op = mpl::lambda<mpl::plus<mpl::_1, mpl::_2>>::type;
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[$images/metaparse/foldl_reject_incomplete_start_with_parser_diag1.png [width 70%]]
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Further details can be found in the
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[link introducing-foldl_reject_incomplete_start_with_parser Introducing foldl_reject_incomplete_start_with_parser]
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section of the [link manual User Manual].
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[h1 Header]
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#include <boost/metaparse/foldl_reject_incomplete_start_with_parser.hpp>
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[h1 Expression semantics]
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For any `p` parser, `pt` class, `f` metafunction class taking two arguments,
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`s` compile-time string and `pos` source position
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foldl_reject_incomplete_start_with_parser<p, pt, f>::apply<s, pos>
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is equivalent to
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first_of<
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foldl_start_with_parser<p, pt, f>,
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fail_at_first_char_expected<p>
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>::apply<s, pos>
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[h1 Example]
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#include <boost/metaparse/foldl_reject_incomplete_start_with_parser.hpp>
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#include <boost/metaparse/lit_c.hpp>
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#include <boost/metaparse/last_of.hpp>
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#include <boost/metaparse/token.hpp>
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#include <boost/metaparse/int_.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/get_result.hpp>
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#include <boost/metaparse/is_error.hpp>
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#include <boost/mpl/lambda.hpp>
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#include <boost/mpl/plus.hpp>
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using namespace boost::metaparse;
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using int_token = token<int_>;
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using plus_token = token<lit_c<'+'>>;
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using plus_int = last_of<plus_token, int_token>;
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using sum_op =
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boost::mpl::lambda<boost::mpl::plus<boost::mpl::_1, boost::mpl::_2>>::type;
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using ints =
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foldl_reject_incomplete_start_with_parser<plus_int, int_token, sum_op>;
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static_assert(
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get_result<
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ints::apply<BOOST_METAPARSE_STRING("11 + 13 + 3 + 21"), start>
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>::type::value == 48,
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"ints should sum the numbers"
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);
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static_assert(
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is_error<
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ints::apply<BOOST_METAPARSE_STRING("11 + 13 + 3 +"), start>
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>::type::value,
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"when the last number is missing, it should be an error"
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);
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[endsect]
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