我想解析（在第一种情况下，仅识别，保留符号）LaTeX数学。现在，我遇到了超级和下标的问题，结合花括号（例如a^{bc}及其组合，我已经基本的a^b工作得很好）。一个最小的例子（尽可能缩短，同时保持可读性）：
#include <iostream>
using std::cout;
#include <string>
using std::string;
#include <boost/spirit/home/x3.hpp>
namespace x3 = boost::spirit::x3;
using x3::space;
using x3::char_;
using x3::lit;
using x3::repeat;
x3::rule<struct scripts, string> scripts = "super- and subscripts";
x3::rule<struct braced_thing, string> braced_thing = "thing optionaly surrounded by curly braces";
x3::rule<struct superscript, string> superscript = "superscript";
x3::rule<struct subscript, string> subscript = "subscript";
// main rule: any number of items with or without braces
auto const scripts_def = *braced_thing;
// second level main rule: optional braces, and any number of characters or sub/superscripts
auto const braced_thing_def = -lit('{') >> *(subscript | superscript | repeat(1)[(char_ - "_^{}")]) >> -lit('}');
// superscript: things of the form a^b where a and b can be surrounded by curly braces
auto const superscript_def = braced_thing >> '^' >> braced_thing;
// subscript: things of the form a_b where a and b can be surrounded by curly braces
auto const subscript_def = braced_thing >> '_' >> braced_thing;
BOOST_SPIRIT_DEFINE(scripts)
BOOST_SPIRIT_DEFINE(braced_thing)
BOOST_SPIRIT_DEFINE(superscript)
BOOST_SPIRIT_DEFINE(subscript)
int main()
{
const string input = "a^{b_x y}_z {v_x}^{{x^z}_y}";
string output; // will only contain the characters as the grammar is defined above
auto first = input.begin();
auto last = input.end();
const bool result = x3::phrase_parse(first, last,
scripts,
space,
output);
if(first != last)
std::cout << "partial match only:\n" << output << '\n';
else if(!result)
std::cout << "parse failed!\n";
else
std::cout << "parsing succeeded:\n" << output << '\n';
}
它也是 Available on Coliru 。
问题是，这个段错误（我肯定有明显的原因）而且我没有别的办法，好吧，用......表达式语法表达。
答案 0 :(得分：5)
我还没有看过@cv_and_he的建议，而是自己调试你的语法。我想出了这个：
auto token = lexeme [ +~char_("_^{} \t\r\n") ];
auto simple = '{' >> sequence >> '}' | token;
auto expr = lexeme [ simple % char_("_^") ];
auto sequence_def = expr % +space;
带给我的是基本上一步一步重新思考/想象实际语法的样子。
我花了两次尝试才能想出正确的
"a b"解析方法（起初我＆＃34;黑客攻击＆＃34;它只是char_(" _^")中的另一个下标运算符但是我得到的印象是不会像你期望的那样导致AST。线索是你在这个空间里使用了一个队长。
目前，没有AST，但我们只是收获了＃34;使用.. x3::raw[...]匹配的原始字符串。
<强> Live Coliru
//#define BOOST_SPIRIT_X3_DEBUG
#include <iostream>
#include <string>
#include <boost/spirit/home/x3.hpp>
namespace x3 = boost::spirit::x3;
namespace grammar {
using namespace x3;
rule<struct _s> sequence { "sequence" };
auto simple = rule<struct _s> {"simple"} = '{' >> sequence >> '}' | lexeme [ +~char_("_^{} \t\r\n") ];
auto expr = rule<struct _e> {"expr"} = lexeme [ simple % char_("_^") ];
auto sequence_def = expr % +space;
BOOST_SPIRIT_DEFINE(sequence)
}
int main() {
for (const std::string input : {
"a",
"a^b", "a_b", "a b",
"{a}^{b}", "{a}_{b}", "{a} {b}",
"a^{b_x y}",
"a^{b_x y}_z {v_x}^{{x^z}_y}"
})
{
std::string output; // will only contain the characters as the grammar is defined above
auto first = input.begin(), last = input.end();
bool result = x3::parse(first, last, x3::raw[grammar::sequence], output);
if (result)
std::cout << "Parse success: '" << output << "'\n";
else
std::cout << "parse failed!\n";
if (last!=first)
std::cout << "remaining unparsed: '" << std::string(first, last) << "'\n";
}
}
输出：
Parse success: 'a'
Parse success: 'a^b'
Parse success: 'a_b'
Parse success: 'a b'
Parse success: '{a}^{b}'
Parse success: '{a}_{b}'
Parse success: '{a} {b}'
Parse success: 'a^{b_x y}'
Parse success: 'a^{b_x y}_z {v_x}^{{x^z}_y}'
启用调试信息的输出：
<sequence>
<try>a</try>
<expr>
<try>a</try>
<simple>
<try>a</try>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: 'a'
<sequence>
<try>a^b</try>
<expr>
<try>a^b</try>
<simple>
<try>a^b</try>
<success>^b</success>
</simple>
<simple>
<try>b</try>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: 'a^b'
<sequence>
<try>a_b</try>
<expr>
<try>a_b</try>
<simple>
<try>a_b</try>
<success>_b</success>
</simple>
<simple>
<try>b</try>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: 'a_b'
<sequence>
<try>a b</try>
<expr>
<try>a b</try>
<simple>
<try>a b</try>
<success> b</success>
</simple>
<success> b</success>
</expr>
<expr>
<try>b</try>
<simple>
<try>b</try>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: 'a b'
<sequence>
<try>{a}^{b}</try>
<expr>
<try>{a}^{b}</try>
<simple>
<try>{a}^{b}</try>
<sequence>
<try>a}^{b}</try>
<expr>
<try>a}^{b}</try>
<simple>
<try>a}^{b}</try>
<success>}^{b}</success>
</simple>
<success>}^{b}</success>
</expr>
<success>}^{b}</success>
</sequence>
<success>^{b}</success>
</simple>
<simple>
<try>{b}</try>
<sequence>
<try>b}</try>
<expr>
<try>b}</try>
<simple>
<try>b}</try>
<success>}</success>
</simple>
<success>}</success>
</expr>
<success>}</success>
</sequence>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: '{a}^{b}'
<sequence>
<try>{a}_{b}</try>
<expr>
<try>{a}_{b}</try>
<simple>
<try>{a}_{b}</try>
<sequence>
<try>a}_{b}</try>
<expr>
<try>a}_{b}</try>
<simple>
<try>a}_{b}</try>
<success>}_{b}</success>
</simple>
<success>}_{b}</success>
</expr>
<success>}_{b}</success>
</sequence>
<success>_{b}</success>
</simple>
<simple>
<try>{b}</try>
<sequence>
<try>b}</try>
<expr>
<try>b}</try>
<simple>
<try>b}</try>
<success>}</success>
</simple>
<success>}</success>
</expr>
<success>}</success>
</sequence>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: '{a}_{b}'
<sequence>
<try>{a} {b}</try>
<expr>
<try>{a} {b}</try>
<simple>
<try>{a} {b}</try>
<sequence>
<try>a} {b}</try>
<expr>
<try>a} {b}</try>
<simple>
<try>a} {b}</try>
<success>} {b}</success>
</simple>
<success>} {b}</success>
</expr>
<success>} {b}</success>
</sequence>
<success> {b}</success>
</simple>
<success> {b}</success>
</expr>
<expr>
<try>{b}</try>
<simple>
<try>{b}</try>
<sequence>
<try>b}</try>
<expr>
<try>b}</try>
<simple>
<try>b}</try>
<success>}</success>
</simple>
<success>}</success>
</expr>
<success>}</success>
</sequence>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: '{a} {b}'
<sequence>
<try>a^{b_x y}</try>
<expr>
<try>a^{b_x y}</try>
<simple>
<try>a^{b_x y}</try>
<success>^{b_x y}</success>
</simple>
<simple>
<try>{b_x y}</try>
<sequence>
<try>b_x y}</try>
<expr>
<try>b_x y}</try>
<simple>
<try>b_x y}</try>
<success>_x y}</success>
</simple>
<simple>
<try>x y}</try>
<success> y}</success>
</simple>
<success> y}</success>
</expr>
<expr>
<try>y}</try>
<simple>
<try>y}</try>
<success>}</success>
</simple>
<success>}</success>
</expr>
<success>}</success>
</sequence>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: 'a^{b_x y}'
<sequence>
<try>a^{b_x y}_z {v_x}^{{</try>
<expr>
<try>a^{b_x y}_z {v_x}^{{</try>
<simple>
<try>a^{b_x y}_z {v_x}^{{</try>
<success>^{b_x y}_z {v_x}^{{x</success>
</simple>
<simple>
<try>{b_x y}_z {v_x}^{{x^</try>
<sequence>
<try>b_x y}_z {v_x}^{{x^z</try>
<expr>
<try>b_x y}_z {v_x}^{{x^z</try>
<simple>
<try>b_x y}_z {v_x}^{{x^z</try>
<success>_x y}_z {v_x}^{{x^z}</success>
</simple>
<simple>
<try>x y}_z {v_x}^{{x^z}_</try>
<success> y}_z {v_x}^{{x^z}_y</success>
</simple>
<success> y}_z {v_x}^{{x^z}_y</success>
</expr>
<expr>
<try>y}_z {v_x}^{{x^z}_y}</try>
<simple>
<try>y}_z {v_x}^{{x^z}_y}</try>
<success>}_z {v_x}^{{x^z}_y}</success>
</simple>
<success>}_z {v_x}^{{x^z}_y}</success>
</expr>
<success>}_z {v_x}^{{x^z}_y}</success>
</sequence>
<success>_z {v_x}^{{x^z}_y}</success>
</simple>
<simple>
<try>z {v_x}^{{x^z}_y}</try>
<success> {v_x}^{{x^z}_y}</success>
</simple>
<success> {v_x}^{{x^z}_y}</success>
</expr>
<expr>
<try>{v_x}^{{x^z}_y}</try>
<simple>
<try>{v_x}^{{x^z}_y}</try>
<sequence>
<try>v_x}^{{x^z}_y}</try>
<expr>
<try>v_x}^{{x^z}_y}</try>
<simple>
<try>v_x}^{{x^z}_y}</try>
<success>_x}^{{x^z}_y}</success>
</simple>
<simple>
<try>x}^{{x^z}_y}</try>
<success>}^{{x^z}_y}</success>
</simple>
<success>}^{{x^z}_y}</success>
</expr>
<success>}^{{x^z}_y}</success>
</sequence>
<success>^{{x^z}_y}</success>
</simple>
<simple>
<try>{{x^z}_y}</try>
<sequence>
<try>{x^z}_y}</try>
<expr>
<try>{x^z}_y}</try>
<simple>
<try>{x^z}_y}</try>
<sequence>
<try>x^z}_y}</try>
<expr>
<try>x^z}_y}</try>
<simple>
<try>x^z}_y}</try>
<success>^z}_y}</success>
</simple>
<simple>
<try>z}_y}</try>
<success>}_y}</success>
</simple>
<success>}_y}</success>
</expr>
<success>}_y}</success>
</sequence>
<success>_y}</success>
</simple>
<simple>
<try>y}</try>
<success>}</success>
</simple>
<success>}</success>
</expr>
<success>}</success>
</sequence>
<success></success>
</simple>
<success></success>
</expr>
<success></success>
</sequence>
Parse success: 'a^{b_x y}_z {v_x}^{{x^z}_y}'