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66 lines
2.0 KiB
66 lines
2.0 KiB
//
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// calc2.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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//
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// PEG syntax:
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//
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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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//
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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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rule EXPRESSION, TERM, FACTOR, TERM_OPERATOR, FACTOR_OPERATOR, NUMBER;
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EXPRESSION <= seq(TERM, zom(seq(TERM_OPERATOR, TERM))), reduce;
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TERM <= seq(FACTOR, zom(seq(FACTOR_OPERATOR, FACTOR))), reduce;
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FACTOR <= cho(NUMBER, seq(chr('('), EXPRESSION, chr(')')));
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TERM_OPERATOR <= cls("+-"), [](const char* s, size_t n) { return (char)*s; };
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FACTOR_OPERATOR <= cls("*/"), [](const char* s, size_t n) { return (char)*s; };
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NUMBER <= oom(cls("0-9")), [](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 (EXPRESSION.parse_and_get_value(expr, val).ret) {
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cout << expr << " = " << val << endl;
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return 0;
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}
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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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