/**
* @param \Helstern\Nomsky\Grammar\Symbol\SymbolSet $set
* @param NormalizedProduction $production
* @param \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets $followSets
* @param \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets $firstSets
*
* @return bool
*/
public function processProduction(SymbolSet $set, NormalizedProduction $production, ParseSets $followSets, ParseSets $firstSets)
{
$rhs = $production->getRightHandSide();
$epsilonAdded = $this->firstSetCalculator->processSymbolList($set, $rhs, $firstSets);
if ($epsilonAdded) {
$lhs = $production->getLeftHandSide();
$otherSet = $followSets->getTerminalSet($lhs);
$set->addAll($otherSet);
}
return $epsilonAdded;
}
/**
* @param \Helstern\Nomsky\Grammar\Symbol\SymbolSet $set
* @param SymbolOccurrence $occurrence
* @param \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets $followSets
* @param \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets $firstSets
*
* @return bool
*/
public function processOccurrence(SymbolSet $set, SymbolOccurrence $occurrence, ParseSets $followSets, ParseSets $firstSets)
{
$symbol = $occurrence->getSymbol();
$isTerminal = SymbolTypeEquals::newInstanceMatchingTerminals();
if ($isTerminal->matchSymbol($symbol)) {
return false;
}
$following = $occurrence->getFollowing();
$epsilonAdded = $this->firstSetCalculator->processSymbolList($set, $following, $firstSets);
if ($epsilonAdded) {
$set->remove(new EpsilonSymbol());
$lhs = $occurrence->getProductionNonTerminal();
$otherSet = $followSets->getTerminalSet($lhs);
$set->addAll($otherSet);
}
return true;
}
/**
* Calculates the first set of the symbol $source and adds it's elements to $set
*
* @param \Helstern\Nomsky\Grammar\Symbol\SymbolSet $set
* @param \Helstern\Nomsky\Grammar\Symbol\Symbol $source
* @param \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets $firstSets
*
* @return boolean if the epsilon symbol was added to $set
*/
public function processSymbol(SymbolSet $set, Symbol $source, ParseSets $firstSets)
{
$symbolIsEpsilon = SymbolIsEpsilon::singletonInstance();
if ($symbolIsEpsilon->matchSymbol($source)) {
$set->add(new EpsilonSymbol());
return true;
}
$symbolsIsNonTerminal = SymbolTypeEquals::newInstanceMatchingNonTerminals();
if ($symbolsIsNonTerminal->matchSymbol($source)) {
$epsilonCounter = new MatchCountingInterceptor($symbolIsEpsilon);
$acceptPredicate = Inverter::newInstance($epsilonCounter);
$otherSet = $firstSets->filterTerminalSet($source, $acceptPredicate);
$set->addAll($otherSet);
if ($epsilonCounter->getMatchCount() > 0) {
$set->add(new EpsilonSymbol());
return true;
}
return false;
}
$set->add($source);
return false;
}
/**
* @return ParseSets
*/
public static function followSets()
{
$sets = new ParseSets([StandardSymbol::nonTerminal('S'), StandardSymbol::nonTerminal('B'), StandardSymbol::nonTerminal('C')]);
$sets->addTerminal(StandardSymbol::nonTerminal('S'), StandardSymbol::terminal('e'));
$sets->addTerminal(StandardSymbol::nonTerminal('S'), new EpsilonSymbol());
$sets->addTerminal(StandardSymbol::nonTerminal('B'), StandardSymbol::terminal('e'));
$sets->addTerminal(StandardSymbol::nonTerminal('B'), new EpsilonSymbol());
$sets->addTerminal(StandardSymbol::nonTerminal('C'), StandardSymbol::terminal('e'));
$sets->addTerminal(StandardSymbol::nonTerminal('C'), new EpsilonSymbol());
return $sets;
}
/**
* @param array|NormalizedProduction[] $productions
* @param Symbol $startSymbol
* @param ParseSets $followSets
* @param ParseSets $firstSets
*
* @return \Helstern\Nomsky\GrammarAnalysis\ParseSets\SetsGenerator
*/
public function generateFollowSets(array $productions, Symbol $startSymbol, ParseSets $followSets, ParseSets $firstSets)
{
$followSets->addEpsilon($startSymbol);
$occurrences = new \ArrayObject();
foreach ($productions as $production) {
$symbol = $production->getLeftHandSide();
$rhs = $production->getRightHandSide();
$this->followSetCalculator->addNonTerminalOccurrences($occurrences, $symbol, $rhs);
}
do {
$changes = false;
/** @var SymbolOccurrence $occurrence */
foreach ($occurrences as $occurrence) {
$set = new ArraySet();
if ($this->followSetCalculator->processOccurrence($set, $occurrence, $followSets, $firstSets)) {
$symbol = $occurrence->getSymbol();
$changes |= $followSets->addAllTerminals($symbol, $set);
}
}
} while ($changes);
return $this;
}
/**
* @param array|Symbol[] $nonTerminals
* @param array|Symbol[][] $parseSets
*
* @return \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets
*/
private function buildFirstSets(array $nonTerminals, array $parseSets)
{
$firstSets = new ParseSets(array_values($nonTerminals));
foreach ($parseSets as $nonTerminal => $listOfTerminals) {
foreach ($listOfTerminals as $terminal) {
$firstSets->addTerminal($nonTerminals[$nonTerminal], $terminal);
}
}
return $firstSets;
}