private static NFA Accept(CharSet acceptCharacters)
{
// Generate a NFA with a simple path with one state transitioning into an accept state.
var nfa = new NFA();
var state = new NFA.State();
nfa.States.Add(state);
var acceptState = new NFA.State { AcceptState = true };
nfa.States.Add(acceptState);
nfa.Transitions.Add(new Transition<NFA.State>(state, acceptState, acceptCharacters));
nfa.StartState = state;
return nfa;
}
private static NFA RepeatOnceOrMore(NFA nfa)
{
// Add an epsilon transition from the accept state back to the start state
NFA.State oldAcceptState = nfa.States.First(f => f.AcceptState);
nfa.Transitions.Add(new Transition<NFA.State>(oldAcceptState, nfa.StartState));
// Add a new accept state, since we cannot have edges exiting the accept state
var newAcceptState = new NFA.State { AcceptState = true };
nfa.Transitions.Add(new Transition<NFA.State>(oldAcceptState, newAcceptState));
nfa.States.Add(newAcceptState);
// Clear the accept flag of the old accept state
oldAcceptState.AcceptState = false;
return nfa;
}
public static NFA RepeatZeroOrMore(NFA input)
{
var nfa = new NFA();
// Add everything from the input
nfa.AddAll(input);
// Create a new starting state, link it to the old accept state with Epsilon
nfa.StartState = new NFA.State();
nfa.States.Add(nfa.StartState);
NFA.State oldAcceptState = input.States.First(f => f.AcceptState);
nfa.Transitions.Add(new Transition<NFA.State>(nfa.StartState, oldAcceptState));
// Add epsilon link from old accept state of input to start, to allow for repetition
nfa.Transitions.Add(new Transition<NFA.State>(oldAcceptState, input.StartState));
// Create new accept state, link old accept state to new accept state with epsilon
var acceptState = new NFA.State { AcceptState = true };
nfa.States.Add(acceptState);
oldAcceptState.AcceptState = false;
nfa.Transitions.Add(new Transition<NFA.State>(oldAcceptState, acceptState));
return nfa;
}
public static NFA Or(NFA a, NFA b)
{
var nfa = new NFA();
// Composite NFA contains all the and all edges in both NFAs
nfa.AddAll(a);
nfa.AddAll(b);
// Add a start state, link to both NFAs old start state with
// epsilon links
nfa.StartState = new NFA.State();
nfa.States.Add(nfa.StartState);
nfa.Transitions.Add(new Transition<NFA.State>(nfa.StartState, a.StartState));
nfa.Transitions.Add(new Transition<NFA.State>(nfa.StartState, b.StartState));
// Add a new accept state, link all old accept states to the new accept
// state with an epsilon link and remove the accept flag
var newAcceptState = new NFA.State { AcceptState = true };
foreach (var oldAcceptState in nfa.States.Where(f => f.AcceptState))
{
oldAcceptState.AcceptState = false;
nfa.Transitions.Add(new Transition<NFA.State>(oldAcceptState, newAcceptState));
}
nfa.States.Add(newAcceptState);
return nfa;
}
