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