public static NFA Or(NFA a, NFA b)
{
NFA 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
NFA.State newAcceptState = new NFA.State {
AcceptState = true
};
foreach (NFA.State 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);
}
public static NFA RepeatZeroOrMore(NFA input)
{
NFA 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
NFA.State 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 And(NFA first, NFA second)
{
// Create a new NFA and use the first NFAs start state as the starting point
NFA nfa = new NFA {
StartState = first.StartState
};
// Change all links in to first acceptstate to go to seconds
// start state
foreach (Transition <NFA.State> edge in first.Transitions.Where(f => f.To.AcceptState))
{
edge.To = second.StartState;
}
// Remove acceptstate from first
first.States.Remove(first.States.First(f => f.AcceptState));
// Add all states and edges in both NFAs
// Second NFA already has an accept state, there is no need to create another one
nfa.AddAll(first);
nfa.AddAll(second);
return(nfa);
}
public static NFA Merge(IList <NFA> nfas)
{
// Create a new NFA, add everything to it.
NFA merged = new NFA();
foreach (NFA nfa in nfas)
{
merged.AddAll(nfa);
}
// Add a new start state
State state = new State();
merged.States.Add(state);
merged.StartState = state;
// Add epsilon transiontions from the start state to all the previous start states
foreach (NFA nfa in nfas)
{
merged.Transitions.Add(new Transition <State>(state, nfa.StartState));
}
return(merged);
}
