private static bool CheckIfStackIsEmpty <U, V>(PDA <U, V> pda, Transition <U, V> epsilonTransition, VirtualConfiguration <U, V> currentConfig) where U : IEquatable <U> where V : IEquatable <V>
{
if (currentConfig.stack.Count() == 0)
{
pda.RemoveTransition(epsilonTransition);
pda.AddTransition().From(epsilonTransition.Origin.Id).To(currentConfig.state.Id).Read().Pop(epsilonTransition.StackSymbolIn).Push();
return(true);
}
return(false);
}
private static bool CheckIfConfigIsStable <U, V>(PDA <U, V> pda, Transition <U, V> epsilonTransition, VirtualConfiguration <U, V> currentConfig) where U : IEquatable <U> where V : IEquatable <V>
{
var enterableTransitions = currentConfig.GetEnterableTransitions();
var enterableEpsilonTransitions = enterableTransitions.Where(t => t.SymbolIn.IsEmpty()).ToList();
Assertion.Assert(enterableEpsilonTransitions.Count <= 1, "a DPDA can only have one enterable epsilon transition in each configuration");
if (enterableEpsilonTransitions.Count == 0)
{
pda.RemoveTransition(epsilonTransition);
foreach (var transition in enterableTransitions)
{
Assertion.Assert(!transition.SymbolIn.IsEmpty(), "there should be no epsilon transitions at this point");
var newStack = transition.StackSymbolsWritten.Concat(currentConfig.stack.Skip(1).ToList()).ToList();
pda.AddTransition().From(epsilonTransition.Origin.Id).To(transition.Target.Id).Read(transition.SymbolIn).Pop(epsilonTransition.StackSymbolIn).Push(newStack);
}
return(true);
}
return(false);
}
/// <summary>
/// checks whether a circle, that does not decrease the stack, was finished for the second time
/// </summary>
/// <param name="pda">DPDA</param>
/// <param name="epsilonTransition">the initial transition which is examined</param>
/// <param name="configPath">the path with all configurations</param>
/// <returns></returns>
private static bool CheckIfTransitionIsUseless <U, V>(PDA <U, V> pda, Transition <U, V> epsilonTransition, List <VirtualConfiguration <U, V> > configPath) where U : IEquatable <U> where V : IEquatable <V>
{
var currentConfig = configPath.Last();
var potentialCircleStarts = ((IEnumerable <VirtualConfiguration <U, V> >)configPath).Reverse().Skip(1).Where(c => c.IsStartOfNotDecreasingCircle(currentConfig)).ToList();
return(potentialCircleStarts.Any(circleStartConfig =>
{
var i = configPath.IndexOf(circleStartConfig);
var circleTransitions = configPath.Skip(i + 1).Select(c => c.transitionToHere).ToList();
if (i >= circleTransitions.Count())
{
var potentialLastCircleRun = configPath.Skip(i + 1 - circleTransitions.Count).Take(circleTransitions.Count).Select(c => c.transitionToHere).ToList();
if (Enumerable.SequenceEqual(circleTransitions, potentialLastCircleRun))
{
pda.RemoveTransition(epsilonTransition);
return true;
}
return false;
}
return false;
}));
}
