用元素的混合物解析化学式

Question

我想使用 boost::spirit 来从原始公式中提取由多种元素组成的化合物的化学计量。在给定的化合物中，我的解析器应该能够区分三种化学元素模式：

由自然丰度的同位素混合物制成的天然元素
纯同位素
非自然丰度的同位素混合物

然后使用这些模式来解析以下化合物：

"C" --> 由天然丰度的 C[12] 和 C[13] 组成的天然碳
"CH4" --> 由天然碳和氢组成的甲烷
"C2H{H[1](0.8)H[2](0.2)}6" --> 由天然 C 和非天然 H 制成的乙烷，由 80% 的氢和 20% 的氘制成
"U[235]" --> 纯铀 235

显然，化学元素模式可以是任何顺序（例如 CH[1]4 和 H[1]4C ...）和频率。

我编写了我的解析器，它非常接近于完成这项工作，但我仍然面临一个问题。

这是我的代码：

template <typename Iterator>
struct ChemicalFormulaParser : qi::grammar<Iterator,isotopesMixture(),qi::locals<isotopesMixture,double>>
{
    ChemicalFormulaParser(): ChemicalFormulaParser::base_type(_start)
    {

        namespace phx = boost::phoenix;

        // Semantic action for handling the case of pure isotope    
        phx::function<PureIsotopeBuilder> const build_pure_isotope = PureIsotopeBuilder();
        // Semantic action for handling the case of pure isotope mixture   
        phx::function<IsotopesMixtureBuilder> const build_isotopes_mixture = IsotopesMixtureBuilder();
        // Semantic action for handling the case of natural element   
        phx::function<NaturalElementBuilder> const build_natural_element = NaturalElementBuilder();

        phx::function<UpdateElement> const update_element = UpdateElement();

        // 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.getProperty<std::string>("symbol"),isotope.second.getProperty<std::string>("symbol"));
        }

        _mixtureToken = "{" >> +(_isotopeNames >> "(" >> qi::double_ >> ")") >> "}";
        _isotopesMixtureToken = (_elementSymbols[qi::_a=qi::_1] >> _mixtureToken[qi::_b=qi::_1])[qi::_pass=build_isotopes_mixture(qi::_val,qi::_a,qi::_b)];

        _pureIsotopeToken = (_isotopeNames[qi::_a=qi::_1])[qi::_pass=build_pure_isotope(qi::_val,qi::_a)];
        _naturalElementToken = (_elementSymbols[qi::_a=qi::_1])[qi::_pass=build_natural_element(qi::_val,qi::_a)];

        _start = +( ( (_isotopesMixtureToken | _pureIsotopeToken | _naturalElementToken)[qi::_a=qi::_1] >>
                      (qi::double_|qi::attr(1.0))[qi::_b=qi::_1])[qi::_pass=update_element(qi::_val,qi::_a,qi::_b)] );

    }

    //! 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;
};

基本上，每个单独的元素模式都可以通过它们各自的语义动作进行正确解析，这些语义动作会在构建化合物的同位素与其相应的化学计量之间生成映射作为输出。解析以下化合物时问题开始：

CH{H[1](0.9)H[2](0.4)}

在这种情况下，语义动作 build_isotopes_mixture return false 因为 0.9+0.4 对于比率之和是没有意义的。因此，我会期望并希望我的解析器因该化合物而失败。然而，由于 _start 规则对三种化学元素模式使用替代运算符，解析器设法通过 1) 丢弃 {H[1](0.9)H[2](0.4)} 部分 2) 保留前面的 [=15] 来解析它=] 3) 使用 _naturalElementToken 解析它。我的语法不够清晰，无法表达为解析器吗？如何以这样的方式使用替代运算符，即当发现但给出 false 时运行语义操作，解析器停止？

Answer 1

How to use the alternative operator in such a way that, when an occurrence has been found but gave a false when running the semantic action, the parser stops ?

通常，您可以通过添加 expectation point 来防止回溯来实现此目的。

在这种情况下你实际上是"conflating"几个任务：

匹配输入
解释匹配的输入
正在验证匹配的输入

Spirit 擅长匹配输入，拥有在口译方面有很好的便利（主要是在 AST 创建的意义上）。但是，通过即时验证，事情变得 "nasty"。

我经常重复的一个建议是尽可能考虑分离问题。我会考虑

首先构建输入的直接 AST 表示，
transforming/normalizing/expanding/canonicalizing到更方便或有意义的域表示
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透彻，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的想法的完整示例。相反，我将尽最大努力勾勒出我在开头提到的 期望点 方法。

要编译的模拟示例

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

一般备注：

不需要本地人，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;

你会想要处理 names/symbols 之间的冲突（可能只是通过优先考虑一个或另一个）
符合标准的编译器将需要 template 限定符（除非我完全误解了你的数据结构，在这种情况下我不知道 ChemicalDatabaseManager 的模板参数是什么应该是什么意思）。

Hint, MSVC is not a standards-conforming compiler

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期望点草图

假设 "weights" 需要在 _mixtureToken 规则中加起来达到 100%，我们可以制作 build_isotopes_micture "not dummy" 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，它会通过回溯来阻碍事情的进行。相反，你可以/断言/任何完整的混合物总和为 100%:

_mixtureToken         = "{" >> +(_isotopeNames >> "(" >> double_ >> ")") >> "}" > eps(validate_weight_total(_val));

类似

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") {}
    };
};

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#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";
    }
}

版画

 ============= '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

用元素的混合物解析化学式

parsing chemical formula with mixtures of elements

c++

boost-spirit

chemistry

boost-spirit-qi

要编译的模拟示例

一般备注：

期望点草图