尝试调整boost精神x3 calc示例来解析可以将函数作为参数的函数.但是它没有编译.
namespace client{ namespace ast{
struct ts;
struct fnc;
typedef boost::variant<
ts,boost::recursive_wrapper<fnc>
> node;
struct ts{
unsigned int id;
};
struct fnc{
std::vector<char> id;
std::vector<node> args;
};
}}
BOOST_FUSION_ADAPT_STRUCT(
client::ast::ts,(unsigned int,id)
)
BOOST_FUSION_ADAPT_STRUCT(
client::ast::fnc,(std::vector<char>,id)
(std::vector<client::ast::node>,args)
)
namespace client{
namespace x3 = boost::spirit::x3;
namespace calc_grammar{
using x3::uint_;
using x3::alpha;
using x3::alnum;
using x3::lit;
using x3::char_;
x3::rule<class funct,ast::fnc> const funct("function");
x3::rule<class ts,ast::ts> const ts("timeseries");
x3::rule<class funct_name,std::vector<char>> const funct_name("function_name");
auto const funct_def = funct_name >> lit('(') >> -((ts|funct)%lit(',')) >> lit(')');
auto const ts_def = lit('#') >> uint_ >> lit('#');
auto const funct_name_def = lit('@') >> alpha >> *(alnum|char_('_'));
auto const calc = x3::grammar(
"calc",funct = funct_def,ts = ts_def,funct_name = funct_name_def
);
}
using calc_grammar::calc;
}
error C2665: ‘boost::detail::variant::make_initializer_node::apply::initializer_node::initialize’: none of the 5 overloads could convert all the argument types
在variant.hpp中还有一个用户注释
// NOTE TO USER : // Compile error here indicates that the given type is not // unambiguously convertible to one of the variant's types // (or that no conversion exists).
但我不是更聪明…
解决方法
我发现了这个老问题. X3在同一时间有所演变,尽管我现在也回答一下.
我怀疑主要问题可能与变体成员的(缺少)(隐式)构造函数一起使用.
无论如何,这是一个更轻巧的语法的现场演示：
namespace grammar_def {
using namespace x3;
rule<class funct,ast::fnc> const funct("function");
auto const ts = lexeme [ '#' >> uint_ >> '#' ];
auto const fname = lexeme [ '@' >> raw [ alpha >> *(alnum | '_') ] ];
auto const expr = ts|funct;
auto const funct_def = fname >> '(' >> -expr % ',' >> ')';
BOOST_SPIRIT_DEFINE(funct)
}
我还添加了一些输出流助手.请注意,为了简单起见,我如何将id类型更改为std :: string(在不侵入命名空间std的情况下重载运算符<<对于矢量< char>很难/不可能)：
namespace client { namespace ast {
static std::ostream& operator<<(std::ostream& os,ts const& v) {
using namespace boost::fusion;
return os << tuple_open("") << tuple_close("") << tuple_delimiter("") << as_vector(v);
}
static std::ostream& operator<<(std::ostream& os,fnc const& v) {
using namespace boost::fusion;
return os << tuple_open("") << tuple_close("") << tuple_delimiter("") << as_vector(v);
}
template<typename T>
static std::ostream& operator<<(std::ostream& os,std::vector<T> const& v) {
os << "("; for (auto& el : v) os << (&el==&v[0]?"":",") << el; return os << ")";
}
} }
演示
这有更多(可选)管道,以允许更丰富的调试信息：
//#define BOOST_SPIRIT_X3_DEBUG
#include <iostream>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/fusion/include/as_vector.hpp>
#include <boost/fusion/include/io.hpp>
#include <boost/spirit/home/x3.hpp>
namespace client { namespace ast {
struct ts;
struct fnc;
//using string = std::vector<char>;
using string = std::string; // for easier printing/debugging
struct ts {
unsigned int id;
ts(unsigned id=0):id(id) {}
};
typedef boost::variant<ts,boost::recursive_wrapper<fnc> > node;
struct fnc {
string id;
std::vector<node> args;
};
} }
BOOST_FUSION_ADAPT_STRUCT(client::ast::ts,id)
BOOST_FUSION_ADAPT_STRUCT(client::ast::fnc,id,args)
//namespace std { static ostream& operator<<(ostream&os,vector<char> const& v) { return os.write(&v[0],v.size()); } }
namespace client { namespace ast {
static std::ostream& operator<<(std::ostream& os,") << el; return os << ")";
}
} }
namespace client {
namespace x3 = boost::spirit::x3;
namespace grammar_def {
using namespace x3;
x3::rule<class funct,ast::fnc> const funct("function");
auto const ts // = x3::rule<class ts,ast::ts> {"timeseries"}
= lexeme [ '#' >> uint_ >> '#' ];
auto const fname // = x3::rule<class fname,ast::string> {"function_name"}
= lexeme [ '@' >> raw [ alpha >> *(alnum | '_') ] ];
auto const expr // = rule<struct expr_,ast::node > {"expr"}
= ts|funct;
auto const funct_def = fname >> '(' >> -expr % ',' >> ')';
BOOST_SPIRIT_DEFINE(funct)
}
auto const& grammar = x3::skip(x3::space) [grammar_def::funct];
}
#include <iostream>
int main() {
std::string const s {
"@pow( #1#,\n"
" @trunc(\n"
" @pi ()\n"
" ) )"};
std::cout << "Parsing '" << s << "'\n";
auto f = s.begin();
client::ast::fnc parsed;
if (parse(f,s.end(),client::grammar,parsed)) {
std::cout << "Parse succeeded: " << parsed << "\n";
} else {
std::cout << "Parse Failed\n";
}
if (f != s.end())
std::cout << "Remaining unparsed input: '" << std::string(f,s.end()) << "'\n";
}
打印：
Parsing '@pow( #1#,@trunc(
@pi ()
) )'
Parse succeeded: pow(1,trunc(pi()))
