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43 lines
1.2 KiB
43 lines
1.2 KiB
4 years ago
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#include <peglib.h>
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#include <assert.h>
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#include <iostream>
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using namespace peg;
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using namespace std;
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int main(void) {
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parser parser(R"(
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EXPRESSION <- ATOM (OPERATOR ATOM)* {
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precedence
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L - +
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L / *
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}
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ATOM <- NUMBER / '(' EXPRESSION ')'
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OPERATOR <- < [-+/*] >
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NUMBER <- < '-'? [0-9]+ >
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%whitespace <- [ \t\r\n]*
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)");
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parser["EXPRESSION"] = [](const SemanticValues& sv) -> long {
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auto result = any_cast<long>(sv[0]);
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if (sv.size() > 1) {
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auto ope = any_cast<char>(sv[1]);
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auto num = any_cast<long>(sv[2]);
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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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parser["OPERATOR"] = [](const SemanticValues& sv) { return *sv.c_str(); };
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parser["NUMBER"] = [](const SemanticValues& sv) { return atol(sv.c_str()); };
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long val;
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parser.parse(" -1 + (1 + 2) * 3 - -1", val);
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assert(val == 9);
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}
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