boost spirit qi match multiple elements - c++

Question

I would like to create a parser based on boost spirit qi that will be able to parse a list of integer values. That is obviously extremely easy and there are tons of examples. The list though is a bit smarter than a comma separated list and it could looks like:
17, 5, fibonacci(2, 4), 71, 99, range(5, 7)
the result of the parser should be a std::vector with the following values:
17, 5, 1, 2, 3, 71, 99, 5, 6, 7
Where fibonacci(2, 4) results in 1, 2, 3 and range(5, 7) results in 5, 6, 7
Edit: What I am looking for is if I already have parsers that have an attribute int (say int_) and parsers that have an attribute std::vector fibonacci and range, how I can combine the results in a single parser. Something like:
list %= *(int_ | elements [ fibonacci | range ] );
Where elements to be the magic that will do the necessary magic the results form fibonacci to fit in the list.
Note: I am not looking for solution that includes append functions like
list = *(int_[push_back(_val, _1)] | fibonacci[push_back(_val, _1)] | range[push_back(_val, _1)] ] );

Answer 1

Here's a simplist take: Live On Coliru
typedef std::vector<int64_t> data_t;
value_list = -value_expression % ',';
value_expression = macro | literal;
literal = int_;
macro = (_functions > '(' > value_list > ')')
[ _pass = phx::bind(_1, _2, _val) ];
Where _functions is a qi::symbols table of functions:
qi::symbols<char, std::function<bool(data_t const& args, data_t& into)> > _functions;
Now, note that the input "17, 5, fibonacci(2, 4), 71, 99, range(5, 7)" results in
parse success
data: 17 5 1 2 3 71 99 5 6 7
But you can even get more funky: "range(fibonacci(13, 14))" results in:
parse success
data: 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377
As you can see, it prints the range from [fib(13)..fib(14)] which is [233..377] (Wolfram Alpha).
Full code (including demo implementations of fibonacci and range :)):
//#define BOOST_SPIRIT_DEBUG
#define BOOST_SPIRIT_USE_PHOENIX_V3
#include <boost/fusion/adapted.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/karma.hpp>
#include <boost/spirit/include/phoenix.hpp>
namespace qi = boost::spirit::qi;
namespace karma = boost::spirit::karma;
namespace phx = boost::phoenix;
typedef std::vector<int64_t> data_t;
template <typename It, typename Skipper = qi::space_type>
struct parser : qi::grammar<It, data_t(), Skipper>
{
parser() : parser::base_type(value_list)
{
using namespace qi;
value_list = -value_expression % ',';
value_expression = macro | literal;
literal = int_;
macro = (_functions > '(' > value_list > ')')
[ _pass = phx::bind(_1, _2, _val) ];
_functions.add("fibonacci", &fibonacci);
_functions.add("range", &range);
BOOST_SPIRIT_DEBUG_NODES((value_list)(value_expression)(literal)(macro));
}
private:
static bool fibonacci(data_t const& args, data_t& into) {
// unpack arguments
if (args.size() != 2)
return false;
auto f = args[0], l = args[1];
// iterate
uint64_t gen0 = 0, gen1 = 1, next = gen0 + gen1;
for(auto i = 0u; i <= l; ++i)
{
switch(i) {
case 0: if (i>=f) into.push_back(gen0); break;
case 1: if (i>=f) into.push_back(gen1); break;
default:
{
next = gen0 + gen1;
if (i>=f) into.push_back(next);
gen0 = gen1;
gen1 = next;
break;
}
}
}
// done
return true;
}
static bool range(data_t const& args, data_t& into) {
// unpack arguments
if (args.size() != 2)
return false;
auto f = args[0], l = args[1];
if (l>f)
into.reserve(1 + l - f + into.size());
for(; f<=l; ++f)
into.push_back(f); // to optimize
return true;
}
qi::rule<It, data_t(), Skipper> value_list ;
qi::rule<It, data_t(), Skipper> value_expression, macro;
qi::rule<It, int64_t(), Skipper> literal;
qi::symbols<char, std::function<bool(data_t const& args, data_t& into)> > _functions;
};
bool doParse(const std::string& input)
{
typedef std::string::const_iterator It;
auto f(begin(input)), l(end(input));
parser<It, qi::space_type> p;
data_t data;
try
{
bool ok = qi::phrase_parse(f,l,p,qi::space,data);
if (ok)
{
std::cout << "parse success\n";
std::cout << "data: " << karma::format_delimited(karma::auto_, ' ', data) << "\n";
}
else std::cerr << "parse failed: '" << std::string(f,l) << "'\n";
if (f!=l) std::cerr << "trailing unparsed: '" << std::string(f,l) << "'\n";
return ok;
} catch(const qi::expectation_failure<It>& e)
{
std::string frag(e.first, e.last);
std::cerr << e.what() << "'" << frag << "'\n";
}
return false;
}
int main()
{
assert(doParse("range(fibonacci(13, 14))"));
}