89 lines
2.3 KiB
Plaintext
89 lines
2.3 KiB
Plaintext
[#change_error_message]
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[section change_error_message]
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[h1 Synopsis]
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template <class P, class Msg>
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struct change_error_message;
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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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[[`Msg`] [[link parsing_error_message parsing error message]]]
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]
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[h1 Description]
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It applies `P` on the input. When `P` succeeds, `change_error_message` returns
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the result `P` returns, otherwise `change_error_message` rejects the input and
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the reason will be `Msg`.
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[h1 Header]
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#include <boost/metaparse/change_error_message.hpp>
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[h1 Expression semantics]
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For any `p` parser and `m` parsing error message, `s` compile-time string and
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`pos` source position
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change_error_message<p, msg>::apply<s, pos>
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is equivalent to `p::apply<s, pos>` when `p` accepts the input.
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It is equivalent to `fail<msg>::apply<s, pos>` otherwise.
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[h1 Example]
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#include <boost/metaparse/change_error_message.hpp>
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#include <boost/metaparse/repeated1.hpp>
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#include <boost/metaparse/letter.hpp>
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#include <boost/metaparse/keyword.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/string.hpp>
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#include <boost/metaparse/is_error.hpp>
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#include <boost/metaparse/start.hpp>
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#include <boost/metaparse/get_message.hpp>
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#include <boost/metaparse/define_error.hpp>
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#include <type_traits>
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using namespace boost::metaparse;
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BOOST_METAPARSE_DEFINE_ERROR(name_expected, "Name expected");
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using keyword_name = token<keyword<BOOST_METAPARSE_STRING("name")>>;
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using name_token = token<repeated1<letter>>;
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using name_parser =
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last_of<keyword_name, change_error_message<name_token, name_expected>>;
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static_assert(
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!is_error<
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name_parser::apply<BOOST_METAPARSE_STRING("name Bela"), start>
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>::type::value,
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"name_parser should accept \"name <a name>\""
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);
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static_assert(
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is_error<
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name_parser::apply<BOOST_METAPARSE_STRING("name ?"), start>
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>::type::value,
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"name_parser should reject input when name is a question mark"
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);
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static_assert(
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std::is_same<
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get_message<
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name_parser::apply<BOOST_METAPARSE_STRING("name ?"), start>
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>::type,
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name_expected
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>::type::value,
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"the error message should be the one specified by change_error_message"
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);
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[endsect]
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