cpp-peglib/example/calc5.cc

//
//  calc5.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: calc5 [formula]" << std::endl;
        return 1;
    }

    std::function<long (const Ast&)> eval = [&](const Ast& ast) {
        if (ast.name == "NUMBER") {
            return stol(ast.token);
        } else {
            const auto& nodes = ast.nodes;
            auto result = eval(*nodes[0]);
            if (nodes.size() > 1) {
                auto ope = nodes[1]->token[0];
                auto num = eval(*nodes[2]);
                switch (ope) {
                    case '+': result += num; break;
                    case '-': result -= num; break;
                    case '*': result *= num; break;
                    case '/': result /= num; break;
                }
            }
            return result;
        }
    };

    parser parser(R"(
        EXPRESSION  <- ATOM (OPERATOR ATOM)* {
                         precedence
                           L - +
                           L / *
                       }
        ATOM        <- NUMBER / '(' EXPRESSION ')'
        OPERATOR    <- < [-+/*] >
        NUMBER      <- < '-'? [0-9]+ >
        %whitespace <- [ \t\r\n]*
    )");

    parser.enable_ast();

    auto expr = argv[1];
    std::shared_ptr<Ast> ast;
    if (parser.parse(expr, ast)) {
        ast = AstOptimizer(true).optimize(ast);
        std::cout << ast_to_s(ast);
        std::cout << expr << " = " << eval(*ast) << std::endl;
        return 0;
    }

    std::cout << "syntax error..." << std::endl;

    return -1;
}

// vim: et ts=4 sw=4 cin cino={1s ff=unix