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51 lines
1.2 KiB
51 lines
1.2 KiB
#include <assert.h>
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#include <iostream>
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#include <peglib.h>
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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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// (2) Make a parser
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parser parser(R"(
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# Grammar for Calculator...
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Additive <- Multitive '+' Additive / Multitive
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Multitive <- Primary '*' Multitive / Primary
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Primary <- '(' Additive ')' / Number
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Number <- < [0-9]+ >
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%whitespace <- [ \t]*
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)");
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assert(static_cast<bool>(parser) == true);
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// (3) Setup actions
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parser["Additive"] = [](const SemanticValues &vs) {
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switch (vs.choice()) {
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case 0: // "Multitive '+' Additive"
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return any_cast<int>(vs[0]) + any_cast<int>(vs[1]);
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default: // "Multitive"
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return any_cast<int>(vs[0]);
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}
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};
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parser["Multitive"] = [](const SemanticValues &vs) {
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switch (vs.choice()) {
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case 0: // "Primary '*' Multitive"
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return any_cast<int>(vs[0]) * any_cast<int>(vs[1]);
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default: // "Primary"
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return any_cast<int>(vs[0]);
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}
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};
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parser["Number"] = [](const SemanticValues &vs) {
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return vs.token_to_number<int>();
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};
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// (4) Parse
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parser.enable_packrat_parsing(); // Enable packrat parsing.
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int val;
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parser.parse(" (1 + 2) * 3 ", val);
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assert(val == 9);
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}
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