cpp-peglib/example/calc2.cc

//
//  calc2.cc
//
//  Copyright (c) 2015 Yuji Hirose. All rights reserved.
//  MIT License
//

#include <cstdlib>
#include <iostream>
#include <peglib.h>

using namespace peg;

//
//  PEG syntax:
//
//      EXPRESSION       <-  TERM (TERM_OPERATOR TERM)*
//      TERM             <-  FACTOR (FACTOR_OPERATOR FACTOR)*
//      FACTOR           <-  NUMBER / '(' EXPRESSION ')'
//      TERM_OPERATOR    <-  [-+]
//      FACTOR_OPERATOR  <-  [/*]
//      NUMBER           <-  [0-9]+
//
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 &vs) {
    auto result = std::any_cast<long>(vs[0]);
    for (auto i = 1u; i < vs.size(); i += 2) {
      auto num = std::any_cast<long>(vs[i + 1]);
      auto ope = std::any_cast<char>(vs[i]);
      switch (ope) {
      case '+': result += num; break;
      case '-': result -= num; break;
      case '*': result *= num; break;
      case '/': result /= num; break;
      }
    }
    return result;
  };

  Definition EXPRESSION, TERM, FACTOR, TERM_OPERATOR, FACTOR_OPERATOR, NUMBER;

  EXPRESSION <= seq(TERM, zom(seq(TERM_OPERATOR, TERM))), reduce;
  TERM <= seq(FACTOR, zom(seq(FACTOR_OPERATOR, FACTOR))), reduce;
  FACTOR <= cho(NUMBER, seq(chr('('), EXPRESSION, chr(')')));
  TERM_OPERATOR <= cls("+-"),
      [](const SemanticValues &vs) { return static_cast<char>(*vs.sv().data()); };
  FACTOR_OPERATOR <= cls("*/"),
      [](const SemanticValues &vs) { return static_cast<char>(*vs.sv().data()); };
  NUMBER <= oom(cls("0-9")),
      [](const SemanticValues &vs) { return vs.token_to_number<long>(); };

  auto expr = argv[1];
  long val = 0;
  if (EXPRESSION.parse_and_get_value(expr, val).ret) {
    std::cout << expr << " = " << val << std::endl;
    return 0;
  }

  return -1;
}

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