private void Form1_Load(object sender, EventArgs e)
{
Console.WriteLine(Notation.infixToPostfix("abb+(abb)+"));
NFA n = Compiler.Compile(Notation.infixToPostfix("(a|b)*"));
Console.WriteLine("AHH");
// DEBUG CODE
}
/// <summary>
/// Creates an alternation between this NFA and the given NFA
/// </summary>
/// <param name="secondNFA">NFA being alternated with this NFA</param>
public void Alternation(NFA secondNFA)
{
// alternating NFAs requires we make a new start state that has epsilon transitions to
// both of the given NFAs
// create new start state (not accepting)
State newStart = new State(false);
// add epsilon transitions from the new start to the start of the two original NFAs
newStart.AddTransition(Transition.Epsilon, this.GetStart());
newStart.AddTransition(Transition.Epsilon, secondNFA.GetStart());
// make the start of this NFA the new start state
this.SetStart(newStart);
}
/// <summary>
/// Concatenates the given NFA to the end of this NFA
/// </summary>
/// <param name="appendingNFA">NFA being appended to the end of this NFA</param>
public void Concatenate(NFA appendingNFA)
{
// when concatenating two NFAs, accepting states of the first NFA
// are given epsilon transitions to the start state of the seconds NFA
// keep a list of visited states so we don't add states over and over
List <State> visited = new List <State>();
// reference to the current state we're working with
State curState;
// queue of states to be checked
Queue <State> stateQueue = new Queue <State>();
stateQueue.Enqueue(this.GetStart());
// while states exist in the queue, continue to loop
while (stateQueue.Count > 0)
{
curState = stateQueue.Dequeue();
if (visited.Contains(curState))
{
continue;
}
// add this state to the list of visited states
visited.Add(curState);
// queue up all states that can be transitioned to
foreach (Transition t in curState.GetTransitions())
{
stateQueue.Enqueue(t.GetState());
}
// if this state is accepting, add an epsilon transition to the start of
// the appendingNFA
if (curState.IsAccepting())
{
curState.AddTransition(Transition.Epsilon, appendingNFA.GetStart());
// this state is no longer accepting
curState.SetAccepting(false);
}
}
}
//TODO make this work f****r
public static NFA Compile(string postfix)
{
// stack that stores NFA pieces
Stack <NFA> nfaStack = new Stack <NFA>();
// go through postfix notation
foreach (char c in postfix.ToCharArray())
{
switch (c)
{
// concatenate
case Notation.CONCAT_OP:
// pop previous two items on stack
NFA nCat1 = nfaStack.Pop();
NFA nCat2 = nfaStack.Pop();
// make them one item
nCat2.Concatenate(nCat1); //TODO make sure this is the right order
// push it onto the stack
nfaStack.Push(nCat2);
break;
// kleene star
case '*':
NFA nStar = nfaStack.Pop();
nStar.KleeneStar();
nfaStack.Push(nStar);
break;
// alternation
case '|':
NFA nAlt1 = nfaStack.Pop();
NFA nAlt2 = nfaStack.Pop();
nAlt2.Alternation(nAlt1);
nfaStack.Push(nAlt2);
break;
// kleene plus
case '+':
//TODO future implementation
break;
// standard character
default:
// make new NFA piece containing 'c' and push it to the NFA stack
// we make an NFA in the format:
// -> O -a-> O
// where the second state is accepting
State start = new State(false);
State transState = new State(true);
start.AddTransition(c, transState);
nfaStack.Push(new NFA(start));
break;
}
}
return(nfaStack.Pop());
}
