119 lines
3.3 KiB
C++
119 lines
3.3 KiB
C++
#include "Parsodus/util/firstset.h"
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#include "Parsodus/grammar.h"
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namespace pds {
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namespace util {
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FirstSet::FirstSet(const Grammar& g)
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{
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for (std::string term : g.terminals) {
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m_first[term].insert(term);
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}
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bool changes = true;
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auto update = [&changes, this](std::string head, const std::set<std::string>& s) {
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for (std::string elem : s) {
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if (!m_first[head].count(elem)) {
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changes = true;
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m_first[head].insert(s.begin(), s.end());
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return;
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}
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}
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};
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while (changes) {
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changes = false;
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for (const auto& rule : g.rules) {
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if (rule->tail.size() == 0) {
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update(rule->head, {""});
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}
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bool ended = false;
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const std::string& head = rule->head;
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for (const std::string& replacement : rule->tail) {
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if (m_first[replacement].count("")) {
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std::set<std::string> tmp = m_first[replacement];
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tmp.erase("");
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update(head, tmp);
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} else {
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update(head, m_first[replacement]);
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ended = true;
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break;
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}
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}
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if (!ended) {
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update(head, {""});
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}
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}
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}
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}
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std::set<std::string> FirstSet::operator()(std::string key) const {
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auto tmp = m_first.find(key);
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if (tmp == m_first.end())
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return {};
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return tmp->second;
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}
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std::set<std::string> FirstSet::operator()(std::vector<std::string> sequence) const {
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std::set<std::string> result;
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bool hasEmpty = false;
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for (std::string key : sequence) {
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std::set<std::string> tmp = (*this)(key);
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hasEmpty = tmp.count("");
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tmp.erase("");
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result.insert(tmp.begin(), tmp.end());
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if (!hasEmpty)
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break;
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}
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if (hasEmpty)
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result.insert("");
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return result;
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}
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/*
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* template <typename Item>
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* void Generator<Item>::buildFollow() {
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* //EOF follow the added start rule.
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* m_follow[EXTENDED_START].insert(EOF_PLACEHOLDER);
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*
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* bool changes = true;
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*
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* auto update = [&changes, this](std::string head, auto s) {
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* s.erase("");
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* for (std::string elem : s) {
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* if (!m_follow[head].count(elem)) {
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* changes = true;
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* m_follow[head].insert(s.begin(), s.end());
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* return;
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* }
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* }
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* };
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*
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* while (changes) {
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* changes = false;
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* for (const auto& p : m_gram.rules) {
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* std::string& head = p.first;
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* for (const auto& rule : p.second) {
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* for (std::size_t i = 0; i < rule.tail.size(); i++) {
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* if (!m_gram.terminals.count(rule.tail[i])) {
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* if (i == rule.tail.size() - 1 || m_first[rule.tail[i + 1]].count("")) {
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* update(rule.tail[i], m_follow[head]);
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* }
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* if (i < rule.tail.size() - 1) {
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* update(rule.tail[i], m_first[rule.tail[i + 1]]);
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* }
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* }
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* }
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* }
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* }
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* }
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* }
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*/
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} /* util */
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} /* pds */
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