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<?php |
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declare(strict_types=1); |
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namespace Remorhaz\UniLex\Parser\LL1\Lookup; |
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use Remorhaz\UniLex\Exception; |
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use Remorhaz\UniLex\Grammar\ContextFree\GrammarInterface; |
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use Remorhaz\UniLex\Grammar\ContextFree\Production; |
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class TableConflictChecker |
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{ |
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private $grammar; |
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private $first; |
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private $follow; |
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public function __construct(GrammarInterface $grammar, FirstInterface $first, FollowInterface $follow) |
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{ |
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$this->grammar = $grammar; |
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$this->first = $first; |
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$this->follow = $follow; |
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} |
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/** |
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* @throws Exception |
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*/ |
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public function check(): void |
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{ |
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foreach ($this->grammar->getNonTerminalList() as $symbolId) { |
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$this->checkSymbolConflicts($symbolId); |
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} |
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} |
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/** |
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* @param int $symbolId |
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* @throws Exception |
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*/ |
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private function checkSymbolConflicts(int $symbolId): void |
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{ |
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$productionList = $this->grammar->getProductionList($symbolId); |
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$this->checkMultipleEpsilons($symbolId, ...$productionList); |
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foreach ($productionList as $alpha) { |
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foreach ($productionList as $beta) { |
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$this->checkProductionConflicts($alpha, $beta); |
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} |
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} |
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} |
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/** |
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* @param Production $alpha |
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* @param Production $beta |
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* @throws Exception |
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*/ |
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private function checkProductionConflicts(Production $alpha, Production $beta): void |
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{ |
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if ($alpha->getIndex() == $beta->getIndex()) { |
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return; |
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} |
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$this->checkFirstFirstConflict($alpha, $beta); |
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$this->checkFirstFollowConflict($alpha, $beta); |
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} |
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/** |
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* @param int $symbolId |
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* @param Production ...$productionList |
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* @throws Exception |
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*/ |
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private function checkMultipleEpsilons(int $symbolId, Production ...$productionList): void |
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{ |
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$isEpsilonProduction = function (Production $production): bool { |
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return $production->isEpsilon(); |
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}; |
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$epsilonProductionList = array_filter($productionList, $isEpsilonProduction); |
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if (count($epsilonProductionList) > 1) { |
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throw new Exception("Symbol {$symbolId} has multiple ε-productions"); |
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} |
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} |
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/** |
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* @param Production $alpha |
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* @param Production $beta |
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* @throws Exception |
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*/ |
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private function checkFirstFirstConflict(Production $alpha, Production $beta): void |
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{ |
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$firstAlpha = $this->first->getProductionTokens(...$alpha->getSymbolList()); |
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$firstBeta = $this->first->getProductionTokens(...$beta->getSymbolList()); |
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$message = "FIRST({$alpha})/FIRST({$beta}) conflict"; |
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$this->checkConflict($firstAlpha, $firstBeta, $message); |
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} |
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/** |
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* @param Production $alpha |
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* @param Production $beta |
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* @throws Exception |
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*/ |
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private function checkFirstFollowConflict(Production $alpha, Production $beta): void |
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{ |
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if (!$this->first->productionHasEpsilon(...$beta->getSymbolList())) { |
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return; |
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} |
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$follow = $this->follow->getTokens($alpha->getHeaderId()); |
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$firstAlpha = $this->first->getProductionTokens(...$alpha->getSymbolList()); |
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$message = "FIRST({$alpha})/FOLLOW({$alpha->getHeaderId()}) conflict (ε ∈ {$beta})"; |
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$this->checkConflict($follow, $firstAlpha, $message); |
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} |
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/** |
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* @param array $tokenListA |
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* @param array $tokenListB |
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* @param string $message |
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* @throws Exception |
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*/ |
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private function checkConflict(array $tokenListA, array $tokenListB, string $message): void |
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{ |
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$conflict = array_intersect($tokenListA, $tokenListB); |
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if (!empty($conflict)) { |
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$conflictText = implode(', ', $conflict); |
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throw new Exception("{$message}: {$conflictText}"); |
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} |
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} |
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} |
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remorhaz /
php-unilex
