如何以这样一种方式使用替代运算符，当发现一个事件但在运行语义操作时给出错误时，解析器停止？
通常，您可以通过添加期望点来防止回溯来实现这一点。
在这种情况下，您实际上是在“合并”几个任务：
- 匹配输入
- 解释匹配的输入
- 验证匹配的输入
Spirit 擅长匹配输入，在解释方面有很好的设施（主要是在 AST 创建的意义上）。但是，动态验证会变得“令人讨厌”。
我经常重复的一个建议是尽可能考虑分离关注点。我会考虑
- 首先构建输入的直接 AST 表示，
- 转换/规范化/扩展/规范化为更方便或更有意义的域表示
- 对结果进行最终验证
这为您提供了最具表现力的代码，同时保持其高度可维护性。
因为我对问题域的理解不够好，而且代码示例还不够完整，无法归纳出它，所以我不会尝试给出我所想的完整示例。相反，我会尽力勾勒出我一开始提到的期望点方法。
模拟样本编译
这花费了最多的时间。（考虑为要帮助你的人做腿部工作）
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#include <boost/fusion/adapted/std_pair.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <map>
namespace qi = boost::spirit::qi;
struct DummyBuilder {
using result_type = bool;
template <typename... Ts>
bool operator()(Ts&&...) const { return true; }
};
struct PureIsotopeBuilder : DummyBuilder { };
struct IsotopesMixtureBuilder : DummyBuilder { };
struct NaturalElementBuilder : DummyBuilder { };
struct UpdateElement : DummyBuilder { };
struct Isotope {
std::string getName() const { return _name; }
Isotope(std::string const& name = "unnamed", std::string const& symbol = "?") : _name(name), _symbol(symbol) { }
template <typename T> std::string getProperty(std::string const& name) const {
if (name == "symbol")
return _symbol;
throw std::domain_error("no such property (" + name + ")");
}
private:
std::string _name, _symbol;
};
using MixComponent = std::pair<Isotope, double>;
using isotopesMixture = std::list<MixComponent>;
template <typename Isotope>
struct ChemicalDatabaseManager {
static ChemicalDatabaseManager* Instance() {
static ChemicalDatabaseManager s_instance;
return &s_instance;
}
auto& getDatabase() { return _db; }
private:
std::map<int, Isotope> _db {
{ 1, { "H[1]", "H" } },
{ 2, { "H[2]", "H" } },
{ 3, { "Carbon", "C" } },
{ 4, { "U[235]", "U" } },
};
};
template <typename Iterator>
struct ChemicalFormulaParser : qi::grammar<Iterator, isotopesMixture(), qi::locals<isotopesMixture, double> >
{
ChemicalFormulaParser(): ChemicalFormulaParser::base_type(_start)
{
using namespace qi;
namespace phx = boost::phoenix;
phx::function<PureIsotopeBuilder> build_pure_isotope; // Semantic action for handling the case of pure isotope
phx::function<IsotopesMixtureBuilder> build_isotopes_mixture; // Semantic action for handling the case of pure isotope mixture
phx::function<NaturalElementBuilder> build_natural_element; // Semantic action for handling the case of natural element
phx::function<UpdateElement> update_element;
// XML database that store all the isotopes of the periodical table
ChemicalDatabaseManager<Isotope>* imgr = ChemicalDatabaseManager<Isotope>::Instance();
const auto& isotopeDatabase=imgr->getDatabase();
// Loop over the database to the spirit symbols for the isotopes names (e.g. H[1],C[14]) and the elements (e.g. H,C)
for (const auto& isotope : isotopeDatabase) {
_isotopeNames.add(isotope.second.getName(),isotope.second.getName());
_elementSymbols.add(isotope.second.template getProperty<std::string>("symbol"),isotope.second.template getProperty<std::string>("symbol"));
}
_mixtureToken = "{" >> +(_isotopeNames >> "(" >> double_ >> ")") >> "}";
_isotopesMixtureToken = (_elementSymbols[_a=_1] >> _mixtureToken[_b=_1])[_pass=build_isotopes_mixture(_val,_a,_b)];
_pureIsotopeToken = (_isotopeNames[_a=_1])[_pass=build_pure_isotope(_val,_a)];
_naturalElementToken = (_elementSymbols[_a=_1])[_pass=build_natural_element(_val,_a)];
_start = +( ( (_isotopesMixtureToken | _pureIsotopeToken | _naturalElementToken)[_a=_1] >>
(double_|attr(1.0))[_b=_1]) [_pass=update_element(_val,_a,_b)] );
}
private:
//! Defines the rule for matching a prefix
qi::symbols<char, std::string> _isotopeNames;
qi::symbols<char, std::string> _elementSymbols;
qi::rule<Iterator, isotopesMixture()> _mixtureToken;
qi::rule<Iterator, isotopesMixture(), qi::locals<std::string, isotopesMixture> > _isotopesMixtureToken;
qi::rule<Iterator, isotopesMixture(), qi::locals<std::string> > _pureIsotopeToken;
qi::rule<Iterator, isotopesMixture(), qi::locals<std::string> > _naturalElementToken;
qi::rule<Iterator, isotopesMixture(), qi::locals<isotopesMixture, double> > _start;
};
int main() {
using It = std::string::const_iterator;
ChemicalFormulaParser<It> parser;
for (std::string const input : {
"C", // --> natural carbon made of C[12] and C[13] in natural abundance
"CH4", // --> methane made of natural carbon and hydrogen
"C2H{H[1](0.8)H[2](0.2)}6", // --> ethane made of natural C and non-natural H made of 80% of hydrogen and 20% of deuterium
"C2H{H[1](0.9)H[2](0.2)}6", // --> invalid mixture (total is 110%?)
"U[235]", // --> pure uranium 235
})
{
std::cout << " ============= '" << input << "' ===========\n";
It f = input.begin(), l = input.end();
isotopesMixture mixture;
bool ok = qi::parse(f, l, parser, mixture);
if (ok)
std::cout << "Parsed successfully\n";
else
std::cout << "Parse failure\n";
if (f != l)
std::cout << "Remaining input unparsed: '" << std::string(f, l) << "'\n";
}
}
正如给定的那样，它只是打印
============= 'C' ===========
Parsed successfully
============= 'CH4' ===========
Parsed successfully
============= 'C2H{H[1](0.8)H[2](0.2)}6' ===========
Parsed successfully
============= 'C2H{H[1](0.9)H[2](0.2)}6' ===========
Parsed successfully
============= 'U[235]' ===========
Parsed successfully
一般说明：
不需要当地人，只需使用常规占位符：
_mixtureToken = "{" >> +(_isotopeNames >> "(" >> double_ >> ")") >> "}";
_isotopesMixtureToken = (_elementSymbols >> _mixtureToken) [ _pass=build_isotopes_mixture(_val, _1, _2) ];
_pureIsotopeToken = _isotopeNames [ _pass=build_pure_isotope(_val, _1) ];
_naturalElementToken = _elementSymbols [ _pass=build_natural_element(_val, _1) ];
_start = +(
( (_isotopesMixtureToken | _pureIsotopeToken | _naturalElementToken) >>
(double_|attr(1.0)) ) [ _pass=update_element(_val, _1, _2) ]
);
// ....
qi::rule<Iterator, isotopesMixture()> _mixtureToken;
qi::rule<Iterator, isotopesMixture()> _isotopesMixtureToken;
qi::rule<Iterator, isotopesMixture()> _pureIsotopeToken;
qi::rule<Iterator, isotopesMixture()> _naturalElementToken;
qi::rule<Iterator, isotopesMixture()> _start;
您将需要处理名称/符号之间的冲突（可能只是通过优先处理其中一个）
符合标准的编译器将需要template限定符（除非我完全错误地猜测了您的数据结构，在这种情况下，我不知道模板参数ChemicalDatabaseManager应该是什么意思）。
提示，MSVC 不是符合标准的编译器
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期望点草图
假设“权重”需要在规则内加到 100% _mixtureToken，我们可以制作build_isotopes_micture“非虚拟”并添加验证：
struct IsotopesMixtureBuilder {
bool operator()(isotopesMixture&/* output*/, std::string const&/* elementSymbol*/, isotopesMixture const& mixture) const {
using namespace boost::adaptors;
// validate weights total only
return std::abs(1.0 - boost::accumulate(mixture | map_values, 0.0)) < 0.00001;
}
};
但是，正如您所注意到的，它会通过回溯来阻止事情。相反，您可以 /assert/ 任何完整的混合物加起来为 100%：
_mixtureToken = "{" >> +(_isotopeNames >> "(" >> double_ >> ")") >> "}" > eps(validate_weight_total(_val));
有类似的东西
struct ValidateWeightTotal {
bool operator()(isotopesMixture const& mixture) const {
using namespace boost::adaptors;
bool ok = std::abs(1.0 - boost::accumulate(mixture | map_values, 0.0)) < 0.00001;
return ok;
// or perhaps just :
return ok? ok : throw InconsistentsWeights {};
}
struct InconsistentsWeights : virtual std::runtime_error {
InconsistentsWeights() : std::runtime_error("InconsistentsWeights") {}
};
};
Live On Coliru
#include <boost/fusion/adapted/std_pair.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/range/adaptors.hpp>
#include <boost/range/numeric.hpp>
#include <map>
namespace qi = boost::spirit::qi;
struct DummyBuilder {
using result_type = bool;
template <typename... Ts>
bool operator()(Ts&&...) const { return true; }
};
struct PureIsotopeBuilder : DummyBuilder { };
struct NaturalElementBuilder : DummyBuilder { };
struct UpdateElement : DummyBuilder { };
struct Isotope {
std::string getName() const { return _name; }
Isotope(std::string const& name = "unnamed", std::string const& symbol = "?") : _name(name), _symbol(symbol) { }
template <typename T> std::string getProperty(std::string const& name) const {
if (name == "symbol")
return _symbol;
throw std::domain_error("no such property (" + name + ")");
}
private:
std::string _name, _symbol;
};
using MixComponent = std::pair<Isotope, double>;
using isotopesMixture = std::list<MixComponent>;
struct IsotopesMixtureBuilder {
bool operator()(isotopesMixture&/* output*/, std::string const&/* elementSymbol*/, isotopesMixture const& mixture) const {
using namespace boost::adaptors;
// validate weights total only
return std::abs(1.0 - boost::accumulate(mixture | map_values, 0.0)) < 0.00001;
}
};
struct ValidateWeightTotal {
bool operator()(isotopesMixture const& mixture) const {
using namespace boost::adaptors;
bool ok = std::abs(1.0 - boost::accumulate(mixture | map_values, 0.0)) < 0.00001;
return ok;
// or perhaps just :
return ok? ok : throw InconsistentsWeights {};
}
struct InconsistentsWeights : virtual std::runtime_error {
InconsistentsWeights() : std::runtime_error("InconsistentsWeights") {}
};
};
template <typename Isotope>
struct ChemicalDatabaseManager {
static ChemicalDatabaseManager* Instance() {
static ChemicalDatabaseManager s_instance;
return &s_instance;
}
auto& getDatabase() { return _db; }
private:
std::map<int, Isotope> _db {
{ 1, { "H[1]", "H" } },
{ 2, { "H[2]", "H" } },
{ 3, { "Carbon", "C" } },
{ 4, { "U[235]", "U" } },
};
};
template <typename Iterator>
struct ChemicalFormulaParser : qi::grammar<Iterator, isotopesMixture()>
{
ChemicalFormulaParser(): ChemicalFormulaParser::base_type(_start)
{
using namespace qi;
namespace phx = boost::phoenix;
phx::function<PureIsotopeBuilder> build_pure_isotope; // Semantic action for handling the case of pure isotope
phx::function<IsotopesMixtureBuilder> build_isotopes_mixture; // Semantic action for handling the case of pure isotope mixture
phx::function<NaturalElementBuilder> build_natural_element; // Semantic action for handling the case of natural element
phx::function<UpdateElement> update_element;
phx::function<ValidateWeightTotal> validate_weight_total;
// XML database that store all the isotopes of the periodical table
ChemicalDatabaseManager<Isotope>* imgr = ChemicalDatabaseManager<Isotope>::Instance();
const auto& isotopeDatabase=imgr->getDatabase();
// Loop over the database to the spirit symbols for the isotopes names (e.g. H[1],C[14]) and the elements (e.g. H,C)
for (const auto& isotope : isotopeDatabase) {
_isotopeNames.add(isotope.second.getName(),isotope.second.getName());
_elementSymbols.add(isotope.second.template getProperty<std::string>("symbol"), isotope.second.template getProperty<std::string>("symbol"));
}
_mixtureToken = "{" >> +(_isotopeNames >> "(" >> double_ >> ")") >> "}" > eps(validate_weight_total(_val));
_isotopesMixtureToken = (_elementSymbols >> _mixtureToken) [ _pass=build_isotopes_mixture(_val, _1, _2) ];
_pureIsotopeToken = _isotopeNames [ _pass=build_pure_isotope(_val, _1) ];
_naturalElementToken = _elementSymbols [ _pass=build_natural_element(_val, _1) ];
_start = +(
( (_isotopesMixtureToken | _pureIsotopeToken | _naturalElementToken) >>
(double_|attr(1.0)) ) [ _pass=update_element(_val, _1, _2) ]
);
}
private:
//! Defines the rule for matching a prefix
qi::symbols<char, std::string> _isotopeNames;
qi::symbols<char, std::string> _elementSymbols;
qi::rule<Iterator, isotopesMixture()> _mixtureToken;
qi::rule<Iterator, isotopesMixture()> _isotopesMixtureToken;
qi::rule<Iterator, isotopesMixture()> _pureIsotopeToken;
qi::rule<Iterator, isotopesMixture()> _naturalElementToken;
qi::rule<Iterator, isotopesMixture()> _start;
};
int main() {
using It = std::string::const_iterator;
ChemicalFormulaParser<It> parser;
for (std::string const input : {
"C", // --> natural carbon made of C[12] and C[13] in natural abundance
"CH4", // --> methane made of natural carbon and hydrogen
"C2H{H[1](0.8)H[2](0.2)}6", // --> ethane made of natural C and non-natural H made of 80% of hydrogen and 20% of deuterium
"C2H{H[1](0.9)H[2](0.2)}6", // --> invalid mixture (total is 110%?)
"U[235]", // --> pure uranium 235
}) try
{
std::cout << " ============= '" << input << "' ===========\n";
It f = input.begin(), l = input.end();
isotopesMixture mixture;
bool ok = qi::parse(f, l, parser, mixture);
if (ok)
std::cout << "Parsed successfully\n";
else
std::cout << "Parse failure\n";
if (f != l)
std::cout << "Remaining input unparsed: '" << std::string(f, l) << "'\n";
} catch(std::exception const& e) {
std::cout << "Caught exception '" << e.what() << "'\n";
}
}
印刷
============= 'C' ===========
Parsed successfully
============= 'CH4' ===========
Parsed successfully
============= 'C2H{H[1](0.8)H[2](0.2)}6' ===========
Parsed successfully
============= 'C2H{H[1](0.9)H[2](0.2)}6' ===========
Caught exception 'boost::spirit::qi::expectation_failure'
============= 'U[235]' ===========
Parsed successfully