cpp-peglib/example/calc.cc
2019-11-22 13:25:42 +01:00

65 lines
1.9 KiB
C++

//
// calc.cc
//
// Copyright (c) 2015 Yuji Hirose. All rights reserved.
// MIT License
//
#include <peglib.h>
#include <iostream>
#include <cstdlib>
using namespace peg;
int main(int argc, const char** argv)
{
if (argc < 2 || std::string("--help") == argv[1]) {
std::cout << "usage: calc [formula]" << std::endl;
return 1;
}
auto reduce = [](const SemanticValues& sv) -> long {
auto result = any_cast<long>(sv[0]);
for (auto i = 1u; i < sv.size(); i += 2) {
auto num = any_cast<long>(sv[i + 1]);
auto ope = any_cast<char>(sv[i]);
switch (ope) {
case '+': result += num; break;
case '-': result -= num; break;
case '*': result *= num; break;
case '/': result /= num; break;
}
}
return result;
};
parser parser(R"(
EXPRESSION <- _ TERM (TERM_OPERATOR TERM)*
TERM <- FACTOR (FACTOR_OPERATOR FACTOR)*
FACTOR <- NUMBER / '(' _ EXPRESSION ')' _
TERM_OPERATOR <- < [-+] > _
FACTOR_OPERATOR <- < [/*] > _
NUMBER <- < [0-9]+ > _
~_ <- [ \t\r\n]*
)");
parser["EXPRESSION"] = reduce;
parser["TERM"] = reduce;
parser["TERM_OPERATOR"] = [](const SemanticValues& sv) { return static_cast<char>(*sv.c_str()); };
parser["FACTOR_OPERATOR"] = [](const SemanticValues& sv) { return static_cast<char>(*sv.c_str()); };
parser["NUMBER"] = [](const SemanticValues& sv) { return atol(sv.c_str()); };
auto expr = argv[1];
long val = 0;
if (parser.parse(expr, val)) {
std::cout << expr << " = " << val << std::endl;
return 0;
}
std::cout << "syntax error..." << std::endl;
return -1;
}
// vim: et ts=4 sw=4 cin cino={1s ff=unix