private Automaton <S> MakeKleeneClosure(Automaton <S> sfa)
{
if (sfa.IsEmpty || sfa.IsEpsilon)
{
return(this.epsilon);
}
if (sfa.IsKleeneClosure())
{
return(sfa);
}
if (sfa.DoesNotContainWordBoundaries && sfa.InitialStateIsSource && sfa.HasSingleFinalSink)
{
//common case, avoid epsilons in this case
//just destructively make the final state to be the initial state
sfa.RenameInitialState(sfa.FinalState);
return(sfa);
}
int origInitState = sfa.InitialState;
if (!sfa.IsFinalState(sfa.InitialState))//the initial state is not final
{
if (sfa.InitialStateIsSource)
{
//make the current initial state final
sfa.MakeInitialStateFinal();
}
else
{
//add a new initial state that is also final
sfa.AddNewInitialStateThatIsFinal(this.MkStateId());
}
}
//add epsilon transitions from final states to the original initial state
foreach (int state in sfa.GetFinalStates())
{
if (state != sfa.InitialState && state != origInitState)
{
sfa.AddMove(Move <S> .Epsilon(state, origInitState));
}
}
//epsilon loops might have been created, remove them
var sfa1 = sfa.RemoveEpsilonLoops();
if (!sfa.DoesNotContainWordBoundaries)
{
sfa1.AddWordBoundaries(sfa.EnumerateWordBoundaries());
}
return(sfa1);
}
/// <summary>
/// Builds an automaton equivalent to the regex r{m,n}, or r{m,} when n is int.MaxValue;
/// r{0,int.MaxValue} is the same as r*;
/// r{1,int.MaxValue} is the same as r+.
/// </summary>
/// <param name="r">regular expression node</param>
/// <param name="m">lower loop bound</param>
/// <param name="n">upper loop bound</param>
/// <returns></returns>
public Automaton <S> MkLoop(T r, int m, int n)
{
bool start = isBeg;
bool end = isEnd;
isBeg = false;
isEnd = false;
Automaton <S> sfa = Callback(r);
isBeg = start;
isEnd = end;
Automaton <S> loop;
if (m == 0 && sfa.IsEmpty)
{
loop = this.epsilon;
}
else if (m == 0 && n == int.MaxValue) //case: *
{
loop = MakeKleeneClosure(sfa);
}
else if (m == 0 && n == 1) //case: ?
{
;
if (sfa.IsFinalState(sfa.InitialState))
{
return(sfa);
}
else if (sfa.InitialStateIsSource)
{
sfa.MakeInitialStateFinal();
}
else
{
sfa.AddNewInitialStateThatIsFinal(this.MkStateId());
}
loop = sfa;
}
else if (m == 1 && n == 1) //trivial case: r{1,1} = r
{
if (sfa.IsEmpty)
{
return(this.empty);
}
loop = sfa;
}
else if (n == int.MaxValue) //case: + or generally {m,} for m >= 1
{
if (sfa.IsEmpty)
{
return(this.empty);
}
if (sfa.IsFinalState(sfa.InitialState))
{
loop = MakeKleeneClosure(sfa); //the repetition is a loop
}
else
{
List <Automaton <S> > sfas = new List <Automaton <S> >();
for (int i = 0; i < m; i++)
{
//make m fresh copies
sfas.Add(sfa);
sfa = sfa.MakeCopy(this.MkStateId);
}
//the last one is made into a Kleene closure
sfas.Add(MakeKleeneClosure(sfa));
//concatenate them all
loop = ConcatenateSFAs(sfas);
}
}
else //general case {m,n}
{
List <Automaton <S> > sfas = new List <Automaton <S> >();
//List<int> newFinals = new List<int>();
for (int i = 0; i < n; i++)
{
sfas.Add(sfa);
if (i < n - 1)
{
sfa = sfa.MakeCopy(this.MkStateId);
if (i >= m - 1)
{
if (sfa.DoesNotContainWordBoundaries && sfa.InitialStateIsSource && !sfa.IsFinalState(sfa.InitialState))
{
sfa.MakeInitialStateFinal();
}
else
{
sfa.AddNewInitialStateThatIsFinal(this.MkStateId());
}
}
}
}
loop = ConcatenateSFAs(sfas);
if (m == 0)
{
loop.MakeInitialStateFinal();
}
//loop.SetFinalStates(newFinals);
}
loop = ExtendLoop(start, end, loop);
return(loop);
}