带有 post 跳过的惯用完全匹配

Question

post-skipping 最惯用的方法是什么？更具体地说，我想确保在匹配我的最高规则后我的输入中没有 "non-skippable"（垃圾）字符。

auto const blankOrComment
    = ascii::space
    | x3::lexeme ['#' >> *(x3::char_ - x3::eol) >> -x3::eol ]
    ;

auto const program = rule<AstProgram>("program")
    = *(as<AstDefinition> (definition > ";"))
    ;

auto const programEntry = x3::skip(blankOrComment) [program];

一个想法，我认为非常丑陋，如果主迭代器位置不是结束迭代器，则之后对 blankOrComment 进行单独的解析调用。我目前更好的想法是更改根规则：

auto const programEntry = x3::skip(blankOrComment) [program >> x3::omit[*blankOrComment]];

有没有更地道的方法？

Answer 1

最简单的破解方法是添加 >> eps：Live On Coliru

请注意，我会努力使船长更具自我描述性：

auto const skipper
    = space
    | '#' >> *(char_ - eol) >> (eol|eoi) 
    ;

同样，您可以使 postskip hack 更具自我描述性：

    auto const post_skip = eps;
    auto const program = "program" >> post_skip;

Live On Coliru

#include <iostream>
#define BOOST_SPIRIT_X3_DEBUG
#include <boost/spirit/home/x3.hpp>

namespace Parser {
    namespace x3 = boost::spirit::x3;

    namespace rules {
        using namespace x3;

        auto const skipper
            = space
            | '#' >> *(char_ - eol) >> (eol|eoi) 
            ;

        auto const post_skip = eps;
        auto const program = "program" >> post_skip;

    }

    auto const programEntry = x3::skip(rules::skipper) [rules::program];
}

int main() {
    using It = std::string::const_iterator;
    for (std::string const input : {
            "",
            " program ",
            "#hello\n program # comment\n",
    }) {
        It f = input.begin(), l = input.end();

        if(parse(f, l, Parser::programEntry)) {
            std::cout << "Parse success\n";
        } else {
            std::cout << "Parse failed\n";
        }

        std::cout << "Remaining: '" << std::string(f,l) << "'\n";
    }
}

版画

Parse failed
Remaining: ''
Parse success
Remaining: ''
Parse success
Remaining: ''

带有 post 跳过的惯用完全匹配

Idiomatic complete matching with post skipping

c++14

boost-spirit

boost-spirit-x3