/**
* @param NormalizedProduction $production
*
* @return bool
*/
private function directlyGeneratesEpsilon(NormalizedProduction $production)
{
//directly generates epsilon
$answer = $production->count() == 1;
$firstSymbol = $production->getFirstSymbol();
$answer &= SymbolIsEpsilon::singletonInstance()->matchSymbol($firstSymbol);
return $answer;
}
/**
* Calculates the first set of $list and adds it's elements to $set
*
* @param \Helstern\Nomsky\Grammar\Symbol\SymbolSet $newFirstSet
* @param array|NormalizedProduction[] $list
* @param \Helstern\Nomsky\GrammarAnalysis\ParseSets\ParseSets $firstSets
*
* @return bool if the epsilon symbol was added to $set
*/
public function processSymbolList(SymbolSet $newFirstSet, array $list, ParseSets $firstSets)
{
if (0 == count($list)) {
$newFirstSet->add(new EpsilonSymbol());
return true;
}
if (1 == count($list)) {
/** @var Symbol $symbol */
$symbol = $list[0];
return $this->processSymbol($newFirstSet, $symbol, $firstSets);
}
$symbolIsEpsilon = SymbolIsEpsilon::singletonInstance();
$symbolsIsNonTerminal = SymbolTypeEquals::newInstanceMatchingNonTerminals();
/** @var SymbolSet $lastSet */
$lastSet = null;
$epsilonCounter = new MatchCountingInterceptor($symbolIsEpsilon);
$acceptor = Inverter::newInstance($epsilonCounter);
//we assume there is no epsilon symbol in the $list list
$previousSymbol = reset($list);
//add the first non-terminal and continue past this one later on
if ($symbolsIsNonTerminal->matchSymbol($previousSymbol)) {
$lastSet = $firstSets->filterTerminalSet($previousSymbol, $acceptor);
$newFirstSet->addAll($lastSet);
} else {
$newFirstSet->add($previousSymbol);
}
//as long as the previous symbol was a non-terminal, process the next symbol
for (next($list); !is_null(key($list)) && $symbolsIsNonTerminal->matchSymbol($previousSymbol) && $epsilonCounter->getMatchCount() > 0; next($list)) {
$previousSymbol = current($list);
$epsilonCounter = new MatchCountingInterceptor($symbolIsEpsilon);
$acceptor = Inverter::newInstance($epsilonCounter);
if ($symbolsIsNonTerminal->matchSymbol($previousSymbol)) {
$lastSet = $firstSets->filterTerminalSet($previousSymbol, $acceptor);
$newFirstSet->addAll($lastSet);
} else {
$newFirstSet->add($previousSymbol);
}
}
if (is_null(key($list)) && $symbolsIsNonTerminal->matchSymbol($previousSymbol) && $epsilonCounter->getMatchCount() > 0) {
$newFirstSet->add(new EpsilonSymbol());
return true;
}
return false;
}
