public FSA <TValue> CreateRawFsa(AstRootNode root, ORegexOptions options)
{
var result = new FSA <TValue>(root.CaptureGroupNames[0])
{
CaptureNames = root.CaptureGroupNames
};
var start = result.NewState();
var end = result.NewState();
Evaluate(start, end, result, root, options);
result.AddFinal(end);
result.AddStart(start);
return(result);
}
/// <summary>
/// Subset machine that employs the powerset construction or subset construction algorithm.
/// It creates a DFA that recognizes the same language as the given NFA.
/// </summary>
private static FSA <TValue> ToDfa(FSA <TValue> fsa)
{
FSA <TValue> dfa = new FSA <TValue>(fsa.Name)
{
ExactBegin = fsa.ExactBegin,
ExactEnd = fsa.ExactEnd,
CaptureNames = fsa.CaptureNames,
};
// Sets of NFA states which is represented by some DFA state
var markedStates = new HashSet <Set <int> >();
var unmarkedStates = new HashSet <Set <int> >();
// Gives a number to each state in the DFA
var dfaStateNum = new Dictionary <Set <int>, int>();
var nfaInitial = fsa.Q0.ToSet();
// Initially, EpsilonClosure(nfa.initial) is the only state in the DFAs states
// and it's unmarked.
var first = EpsilonClosure(fsa, nfaInitial);
unmarkedStates.Add(first);
// The initial dfa state
int dfaInitial = dfa.NewState();
dfaStateNum[first] = dfaInitial;
dfa.AddStart(dfaInitial);
while (unmarkedStates.Count != 0)
{
// Takes out one unmarked state and posteriorly mark it.
var aState = unmarkedStates.First();
// Removes from the unmarked set.
unmarkedStates.Remove(aState);
// Inserts into the marked set.
markedStates.Add(aState);
// If this state contains the NFA's final state, add it to the DFA's set of
// final states.
if (fsa.F.Any(x => aState.Contains(x)))
{
dfa.AddFinal(dfaStateNum[aState]);
}
// For each input symbol the NFA knows...
foreach (var current in fsa.Sigma)
{
// Next state
var next = EpsilonClosure(fsa, fsa.Move(aState, current));
if (next.Count > 0)
{
// If we haven't examined this state before, add it to the unmarkedStates,
// and make up a new number for it.
if (!unmarkedStates.Contains(next) && !markedStates.Contains(next))
{
unmarkedStates.Add(next);
dfaStateNum.Add(next, dfa.NewState());
}
var from = dfaStateNum[aState];
var to = dfaStateNum[next];
var condition = current;
dfa.AddTransition(from, condition, to);
}
}
}
return(dfa);
}
