和上次一样，我不认为船长是你的问题。
也许是关于船长做什么的假设。
-
space - eol只是blank.
- 词位不跳过（这就是定义）：提升精神船长问题 https://stackoverflow.com/questions/17072987/boost-spirit-skipper-issues/17073965#17073965
- PEG 语法是贪婪的、从左到右的。因此，如果您想避免匹配，则需要确保位于单词边界上
"not"在纯名称中：防止 Boost Spirit Symbol 解析器过早接受关键字 https://stackoverflow.com/questions/21960167/prevent-the-boost-spirit-symbol-parser-from-accepting-a-keyword-too-early/21960899#21960899 or 如何在boostspirit中正确解析保留字 https://stackoverflow.com/questions/20131162/how-to-parse-reserved-words-correctly-in-boost-spirit/20133011#20133011
我会编写更加自我描述的规则（例如eol_skipper建议它跳过eol，但这正是它不会跳过的内容？）。
using Skipper = qi::blank_type;
然后，让你的identifier规则（纯名称？）隐式lexeme只需从声明中删除船长：
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
Live On Coliru http://coliru.stacked-crooked.com/a/16aba7bbfebc410a
#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 failed\n";
if (f!=l)
std::cout << "Remaining unparsed input: '" << std::string(f,l) << "'\n";
}
}
Prints
Parsed a = NOT[_b]
Parsed a = NOT[not_var_name]
NOTE如何定义BOOST_SPIRIT_DEBUG如果您下次想要对规则进行故障排除，还会为您提供调试输出：
<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]
