What is the most idiomatic way to do post-skipping? More specific I want to ensure there is no "non-skippable" (garbage) characters in my input after matching my top rule.
auto const blankOrComment
= ascii::space
| x3::lexeme ['#' >> *(x3::char_ - x3::eol) >> -x3::eol ]
;
auto const program = rule<AstProgram>("program")
= *(as<AstDefinition> (definition > ";"))
;
auto const programEntry = x3::skip(blankOrComment) [program];
One idea, I consider quite ugly was to do a separate parse call for the blankOrComment afterwards, if the main iterator position is not the end iterator. The current better idea I have is to change the root rule:
auto const programEntry = x3::skip(blankOrComment) [program >> x3::omit[*blankOrComment]];
Is there a more idiomatic way?
The simplest hack is to tack on >> eps: Live On Coliru
Note I'd strive to make the skipper more self-descriptive:
auto const skipper
= space
| '#' >> *(char_ - eol) >> (eol|eoi)
;
Likewise you can make that postskip hack more self-descriptive:
auto const post_skip = eps;
auto const program = "program" >> post_skip;
#include <iostream>
#define BOOST_SPIRIT_X3_DEBUG
#include <boost/spirit/home/x3.hpp>
namespace Parser {
namespace x3 = boost::spirit::x3;
namespace rules {
using namespace x3;
auto const skipper
= space
| '#' >> *(char_ - eol) >> (eol|eoi)
;
auto const post_skip = eps;
auto const program = "program" >> post_skip;
}
auto const programEntry = x3::skip(rules::skipper) [rules::program];
}
int main() {
using It = std::string::const_iterator;
for (std::string const input : {
"",
" program ",
"#hello\n program # comment\n",
}) {
It f = input.begin(), l = input.end();
if(parse(f, l, Parser::programEntry)) {
std::cout << "Parse success\n";
} else {
std::cout << "Parse failed\n";
}
std::cout << "Remaining: '" << std::string(f,l) << "'\n";
}
}
Prints
Parse failed
Remaining: ''
Parse success
Remaining: ''
Parse success
Remaining: ''