/** * Lists all occurrences B of a non terminal in the right hand side of a production A -> aBc * * @param \ArrayObject $existing * @param Symbol $lhs * @param array|Symbol[] $rhs * * @return int the number of added occurrences */ public function addNonTerminalOccurrences(\ArrayObject $existing, $lhs, array $rhs) { $isNonTerminal = SymbolTypeEquals::newInstanceMatchingNonTerminals(); $added = 0; $preceding = []; do { $symbol = array_shift($rhs); if ($isNonTerminal->matchSymbol($symbol)) { $occurrence = new SymbolOccurrence($symbol, $preceding, $rhs, $lhs); $existing->append($occurrence); $added++; } else { $preceding[] = $symbol; } } while (count($rhs)); return $added; }
/** * 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; }