/**
* @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 ParseSets $firstSets
* @param SymbolSet $emptySet
*
* @return SetsGenerator
*/
public function generateFirstSets(array $productions, ParseSets $firstSets, SymbolSet $emptySet)
{
//add epsilon to the first sets of the non terminals which generate epsilon
foreach ($productions as $production) {
$lhs = $production->getLeftHandSide();
if ($emptySet->contains($lhs)) {
$firstSets->addEpsilon($lhs);
}
}
//initialize the obvious first sets of productions which start with a terminal
foreach ($productions as $production) {
$symbol = $production->getFirstSymbol();
if ($symbol->getType() == Symbol::TYPE_TERMINAL) {
$firstSets->addTerminal($production->getLeftHandSide(), $symbol);
}
}
//initialize first sets for productions which contain several non-terminals
do {
$changes = false;
foreach ($productions as $production) {
$updateSet = new ArraySet();
$rhs = $production->getRightHandSide();
$this->firstSetCalculator->processSymbolList($updateSet, $rhs, $firstSets);
$nonTerminal = $production->getLeftHandSide();
$changes |= $firstSets->addAllTerminals($nonTerminal, $updateSet);
}
} while ($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;
}
