public static StackAlphabet operator -(StackAlphabet a, Alphabet b)
{
var c = new StackAlphabet();
foreach (var c1 in a)
{
if (!b.Contains(c1))
{
c.Add(c1);
}
}
return(c);
}
/// <param name="q">The set of states</param>
/// <param name="a">The language alphabet</param>
/// <param name="g">The stack alphabet</param>
/// <param name="d">The transition function containing Transition and PushdownTransition objects</param>
/// <param name="q0">The initial state</param>
/// <param name="f">The set of accepting states</param>
/// <exception cref="ArgumentException"></exception>
public PushdownAutomaton(States q, Alphabet a, StackAlphabet g, PushdownTransitionFunction d, State q0, AcceptingStates f)
{
States = q;
Alphabet = a;
StackAlphabet = g;
Transitions = d;
InitialState = q0;
AcceptingStates = f;
if (States.Count == 0)
{
throw new ArgumentException("The set of states cannot be empty.");
}
if (!States.Contains(InitialState))
{
throw new ArgumentException("The inital state does not exist in the set of states!");
}
foreach (var s in AcceptingStates)
{
if (!States.Contains(s))
{
throw new ArgumentException($"The accepting state {s} is not in the set of states!");
}
}
foreach (var t in Transitions)
{
if (!States.Contains(t.P) || !States.Contains(t.Q) ||
(!Alphabet.Contains(t.A) && t.A != Alphabet.EmptyString) ||
(!StackAlphabet.Contains(t.Top) && t.Top != Alphabet.Wildcard && t.Top != Alphabet.EmptyString))
{
throw new ArgumentException($"Invalid transition {t}");
}
if (t.Replace.Length == 1 && ((t.Replace[0] != Alphabet.Wildcard && t.Replace[0] != Alphabet.EmptyString) && !StackAlphabet.Contains(t.Replace[0])))
{
throw new ArgumentException($"Invalid replace char for transition {t}");
}
if (t.Replace.Length > 1 && Array.Exists(t.Replace, x => !StackAlphabet.Contains(x)))
{
throw new ArgumentException($"Invalid replace char sequence for transition {t}");
}
}
}