peg-example.cpp

#include <string>
#include "peglib.h"

using namespace peg;
using namespace std;

int main(void)
{    // (2) Make a parser
	parser parser(R"(
        # Grammar for Calculator...
        Additive    <- Multitive '+' Additive / Multitive
        Multitive   <- Primary '*' Multitive / Primary
        Primary     <- '(' Additive ')' / Number
        Number      <- < [0-9]+ >
        %whitespace <- [ \t]*
    )");

	assert((bool) parser);

	// (3) Setup actions
	parser["Additive"] = [](const SemanticValues& sv) {
		switch (sv.choice()) {
			case 0:  // "Multitive '+' Additive"
				return any_cast<int>(sv[0]) + any_cast<int>(sv[1]);
			default: // "Multitive"
				return any_cast<int>(sv[0]);
		}
	};

	parser["Multitive"] = [](const SemanticValues& sv) {
		switch (sv.choice()) {
			case 0:  // "Primary '*' Multitive"
				return any_cast<int>(sv[0]) * any_cast<int>(sv[1]);
			default: // "Primary"
				return any_cast<int>(sv[0]);
		}
	};

	parser["Number"] = [](const SemanticValues& sv) {
		return stoi(sv.token(), nullptr, 10);
	};

	// (4) Parse
	parser.enable_packrat_parsing(); // Enable packrat parsing.

	int val;
	parser.parse(" (1 + 2) * 3 ", val);

	assert(val == 9);
}