firstOf method

SymbolSet firstOf(String productionName, ProductionsMap allProductions, ProductionTerminals firstList)

Recursive function that receives a productions map and generates the first set for each production

Implementation

SymbolSet firstOf(
  String productionName,
  ProductionsMap allProductions,
  ProductionTerminals firstList,
) {
  if (firstList.containsKey(productionName)) {
    return firstList[productionName]!;
  }
  final firstSet = <String>{};
  firstList[productionName] = firstSet;
  if (!allProductions.containsKey(productionName)) {
    throw ('Production "$productionName" not defined');
  }
  for (final production in allProductions[productionName]!) {
    for (var count = 0; count < production.length; count += 1) {
      if (production[count].tokenType == TokenType.production) {
        // in case first element in allProductions is a sub-production,
        // it will get the first set of it
        final firstOfSubProduction = firstOf(
          production[count].lexeme,
          allProductions,
          firstList,
        );
        joinSets(firstSet, firstOfSubProduction);
        // if sub production doesn't have a empty first, stop loop
        if (!firstOfSubProduction.contains('')) {
          count = production.length + 1;
        }
      } else {
        // if during the loop it gets a terminal symbol, add it to first set
        final token = production[count];
        firstSet.add(token.tokenType != TokenType.genericTerminal
            ? sanitizeTerminal(token.lexeme)
            : token.lexeme);
        count = production.length + 1;
      }
    }
  }

  return firstSet;
}