Recursive descent parser generator: Difference between revisions

Write a recursive descent parser generator that takes a description of a grammar as input and outputs the source code for a parser in the same language as the generator. (So a generator written in C++ would output C++ source code for the parser.) You can assume that all of the rules have been preprocessed into a form suitable for the construction of a recursive descent parser. SeeCheck herethe following links for more details: http://www.cs.engr.uky.edu/~lewis/essays/compilers/rec-des.html

<langsyntaxhighlight lang="cpp">

#include <regexsstream>

if (argc < 3) {

cout << "Usage: <input file> <output file>" << endl;

return 1;

}

ifstream inFile(argv[1]);

ofstream outFile(argv[2]);

regex blankLine(R"(^\s*$)");

regex terminalPattern(R"((\w+)\s+(.+))");

regex rulePattern(R"(^!!\s*(\w+)\s*->\s*((?:\w+\s*)*)$)");

regex argPattern(R"(\$(\d+))");

smatch results;

// Read terminal patterns

string line;

while (true) {

getline(inFile, line);

// Terminals section ends with a blank line

if (regex_match(line, blankLine))

break;

regex_match(line, results, terminalPattern);

terminals[results[1]] = results[2];

}

outFile << "#include <iostream>" << endl;

outFile << "#include <fstream>" << endl;

outFile << "#include <string>" << endl;

outFile << "#include <regex>" << endl;

outFile << "using namespace std;" << endl << endl;

// Generate the token processing functions

outFile << "string input, nextToken, nextTokenValue;" << endl;

outFile << "string prevToken, prevTokenValue;" << endl << endl;

outFile << " prevTokenstatic =regex nextToken" << name << "(R\"(^\\s*(" << pattern << "))\");" << endl;

outFile << " if (regex_match(inputline, results, eof, regex_constants::match_continuousrulePattern)) {" << endl;

outFile << " throw \"Unknown token\";"line << endl;

// Generate thefunction firstsignatures sets,for the inefficientlynonterminals

for (autoint ij = nonterminalRules.begin()0; ij !=< nonterminalRulesi->second.endsize(); ++ij) {

for (auto i = nonterminalRules if (terminals.beginfind(token); i != nonterminalRulesterminals.end(); ++i) {

outFile << " vector<string>if results;(" << endl;

for (int j = 0; j < if (terminals.find(i->second[j][k]) != terminals.sizeend(); ++j) {

outFile << " advanceToken();}" << endl << endl;

outFile << "}int main(int argc, char **argv) {" << endl;