这是使用表达式语法的一小部分。
prefix =
(lit(L"not") >> prefix)
|(lit('-') >> prefix)
| postfix
;
postfix i有 name_pure 以获取标识符。
name_pure = lexeme[+(boost::spirit::standard_wide::alpha | '_') >> *(boost::spirit::standard_wide::alnum | '_')];
到目前为止一切都很好。可以写
之类的东西a=not b
但是，如果我开始使用而不是作为这样的名称前缀
a=not notvarname
我从AST中获得一个解析器，看起来像这样
a=not not varname
这意味着不是用作前缀规则，而不是用规则 name_pure 作为Name。
从我的角度来看，船长看来没有正确涉及。
这是我的船长
template<typename Iterator>
struct eol_skipper : public qi::grammar<Iterator> {
eol_skipper() : eol_skipper::base_type(skip)
{
using qi::eol;
using qi::lit;
using qi::char_;
skip = ascii::space -eol;
}
qi::rule<Iterator> skip;
};
就像上次一样，我认为船长不是您的问题。
关于船长做什么的假设。
-
space - eol只是blank。 - Lexemes不跳过（这是定义）：增强精神船长问题
- 钉语法是贪婪和从左到右的。因此，如果要避免在Purename内部匹配
"not"，则需要确保您处于一个单词边界：防止Boost Spirit Symber Parser过早接受关键字，或者如何以Boost Spirit正确解析保留的单词
我会编写更多的自我描述性（例如eol_skipper建议它跳过eol，但这正是它不会跳过的？）。
using Skipper = qi::blank_type;
然后，通过从声明中删除船长来制作您的 identifier规则（pure_name？）一个隐式 lexeme：
private:
qi::rule<Iterator, Ast::AssignmentStatement()> start;
qi::rule<Iterator, Ast::AssignmentStatement(), Skipper> assignment;
qi::rule<Iterator, Ast::Expr(), Skipper> expr;
qi::rule<Iterator, Ast::Negated(), Skipper> negation;
// implicit lexemes
qi::rule<Iterator, Ast::Identifier()> identifier;
最后，使用!p解析器指令断言not在关键字/标识符边界上匹配：
negation
= lexeme [(lit("not") | '0') >> !(alnum|'_')] >> expr
;
演示时间
活在coliru
#define BOOST_SPIRIT_DEBUG
#include <boost/fusion/adapted/struct.hpp>
#include <boost/spirit/include/qi.hpp>
#include <iostream>
namespace qi = boost::spirit::qi;
namespace Ast {
using Identifier = std::string;
struct Negated;
using Expr = boost::variant<Identifier, boost::recursive_wrapper<Negated> >;
struct Negated {
Expr expr;
};
struct AssignmentStatement {
Identifier lhs;
Expr rhs;
};
}
BOOST_FUSION_ADAPT_STRUCT(Ast::Negated, expr)
BOOST_FUSION_ADAPT_STRUCT(Ast::AssignmentStatement, lhs, rhs)
template <typename Iterator> struct parser : qi::grammar<Iterator, Ast::AssignmentStatement()> {
using Skipper = qi::blank_type;
parser() : parser::base_type(start) {
using namespace qi;
start = skip(blank) [ assignment ];
assignment = identifier >> '=' >> expr;
expr = negation | identifier;
negation
= lexeme [(lit("not") | '0') >> !(alnum|'_')] >> expr
;
identifier = char_("a-zA-Z_") >> *char_("a-zA-Z0-9_");
// or:
identifier = raw [ +(alpha | '_') >> *(alnum | '_') ];
BOOST_SPIRIT_DEBUG_NODES((start)(expr)(assignment)(identifier)(negation))
}
private:
qi::rule<Iterator, Ast::AssignmentStatement()> start;
qi::rule<Iterator, Ast::AssignmentStatement(), Skipper> assignment;
qi::rule<Iterator, Ast::Expr(), Skipper> expr;
qi::rule<Iterator, Ast::Negated(), Skipper> negation;
// implicit lexemes
qi::rule<Iterator, Ast::Identifier()> identifier;
};
namespace Ast {
std::ostream& operator<<(std::ostream& os, Negated const& o) { return os << "NOT[" << o.expr << "]"; }
std::ostream& operator<<(std::ostream& os, AssignmentStatement const& a) { return os << a.lhs << " = " << a.rhs; }
}
int main() {
using It = std::string::const_iterator;
for (std::string const input : {
"a=not _b",
"a=not not_var_name",
})
{
It f = input.begin(), l = input.end();
Ast::AssignmentStatement assignment;
if (parse(f, l, parser<It>{}, assignment))
std::cout << "Parsed " << assignment << "n";
else
std::cout << "Parse failedn";
if (f!=l)
std::cout << "Remaining unparsed input: '" << std::string(f,l) << "'n";
}
}
打印
Parsed a = NOT[_b]
Parsed a = NOT[not_var_name]
NOTE 定义
BOOST_SPIRIT_DEBUG还为您提供调试输出，以防您要对规则进行故障排除，下次：
<start>
<try>a=not b</try>
<assignment>
<try>a=not b</try>
<identifier>
<try>a=not b</try>
<success>=not b</success>
<attributes>[[a]]</attributes>
</identifier>
<expr>
<try>not b</try>
<negation>
<try>not b</try>
<expr>
<try> b</try>
<negation>
<try> b</try>
<fail/>
</negation>
<identifier>
<try>b</try>
<success></success>
<attributes>[[b]]</attributes>
</identifier>
<success></success>
<attributes>[[b]]</attributes>
</expr>
<success></success>
<attributes>[[[b]]]</attributes>
</negation>
<success></success>
<attributes>[[[b]]]</attributes>
</expr>
<success></success>
<attributes>[[[a], [[b]]]]</attributes>
</assignment>
<success></success>
<attributes>[[[a], [[b]]]]</attributes>
</start>
Parsed a = NOT[b]
<start>
<try>a=not notvarname</try>
<assignment>
<try>a=not notvarname</try>
<identifier>
<try>a=not notvarname</try>
<success>=not notvarname</success>
<attributes>[[a]]</attributes>
</identifier>
<expr>
<try>not notvarname</try>
<negation>
<try>not notvarname</try>
<expr>
<try> notvarname</try>
<negation>
<try> notvarname</try>
<fail/>
</negation>
<identifier>
<try>notvarname</try>
<success></success>
<attributes>[[n, o, t, v, a, r, n, a, m, e]]</attributes>
</identifier>
<success></success>
<attributes>[[n, o, t, v, a, r, n, a, m, e]]</attributes>
</expr>
<success></success>
<attributes>[[[n, o, t, v, a, r, n, a, m, e]]]</attributes>
</negation>
<success></success>
<attributes>[[[n, o, t, v, a, r, n, a, m, e]]]</attributes>
</expr>
<success></success>
<attributes>[[[a], [[n, o, t, v, a, r, n, a, m, e]]]]</attributes>
</assignment>
<success></success>
<attributes>[[[a], [[n, o, t, v, a, r, n, a, m, e]]]]</attributes>
</start>
Parsed a = NOT[notvarname]