public FirstSetTable GetFirstSets(BNF bnf)
{
FirstSetTable sets = new FirstSetTable();
foreach (var production in bnf)
{
GetSymbolFirstSet(production.Key, bnf, sets);
}
return(sets);
}
HashSet <string> GetSymbolFirstSet(string symbol, BNF bnf, FirstSetTable firstSets)
{
if (firstSets.SymbolSets.ContainsKey(symbol))
{
return(firstSets.SymbolSets[symbol]);
}
else
{
if (IsTerminal(symbol, bnf))
{
HashSet <string> set = new HashSet <string>()
{
symbol
};
firstSets.SymbolSets.Add(symbol, set);
return(set);
}
else
{
HashSet <string> set = new HashSet <string>();
var expansions = bnf[symbol];
for (int index = 0; index < expansions.Count; index++)
{
var expansionSet = GetExpansionFirstSet(symbol, index, bnf, firstSets);
if (expansions[index].Count == 1 && expansions[index][0] == _emptySymbol)
{
set.Add(_emptySymbol);
}
else
{
set.UnionWith(expansionSet);
}
}
firstSets.SymbolSets.Add(symbol, set);
return(set);
}
}
}
HashSet <string> GetExpansionFirstSet(string production, int expansionIndex, BNF bnf, FirstSetTable firstSets)
{
if (firstSets.ExpansionSets.ContainsKey((production, expansionIndex)))
{
return(firstSets.ExpansionSets[(production, expansionIndex)]);
}