cpp-peglib/example/calc.cc
2020-11-09 13:18:38 -05:00

52 lines
1.2 KiB
C++

#include <assert.h>
#include <iostream>
#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(static_cast<bool>(parser) == true);
// (3) Setup actions
parser["Additive"] = [](const SemanticValues &vs) {
switch (vs.choice()) {
case 0: // "Multitive '+' Additive"
return any_cast<int>(vs[0]) + any_cast<int>(vs[1]);
default: // "Multitive"
return any_cast<int>(vs[0]);
}
};
parser["Multitive"] = [](const SemanticValues &vs) {
switch (vs.choice()) {
case 0: // "Primary '*' Multitive"
return any_cast<int>(vs[0]) * any_cast<int>(vs[1]);
default: // "Primary"
return any_cast<int>(vs[0]);
}
};
parser["Number"] = [](const SemanticValues &vs) {
return vs.token_to_number<int>();
};
// (4) Parse
parser.enable_packrat_parsing(); // Enable packrat parsing.
int val;
parser.parse(" (1 + 2) * 3 ", val);
assert(val == 9);
}