public List <LlConfiguration <TSymbol> > OutgoingEpsiEdges(LlConfiguration <TSymbol> llconf)
{
if (llconf.Count() == 0)
{
// If intially the stack is empty we cannot figure out next edges, so return an empty list.
return(new List <LlConfiguration <TSymbol> > ());
}
var topState = llconf.stack[llconf.stack.Count - 1];
var transitions = topState.Transitions;
var result = new List <LlConfiguration <TSymbol> >();
foreach (var kv in transitions)
{
var symbol = kv.Key;
var targetState = kv.Value;
var newllconf = llconf.Pop(); // a copy without top state
if (!IsTerminal(symbol))
{
newllconf = newllconf.Push(targetState);
newllconf = newllconf.Push(Automatons[symbol].Start);
result.Add(newllconf);
}
}
if (topState.Accepting > 0)
{
// We also add a separate epsilon-edge for the situation in which
// top state is accepting state for some nonterminal's automaton and
// we don't move forward but just pop the top state from the stack.
// then we consider two cases: when the stack is empty and when it's not.
if (llconf.Count() == 1)
{
// prevSymbol is a nonterminal whose DFA contains topState (and topState is accepting)
var prevSymbol = AccStateOwnerDictionary [topState];
var newllconf = llconf.Pop(); // a copy without top state
// browse the list of target states for the prevSymbol and for each of them create
// a separate configuration with the stack containing the given state.
if (TargetStatesDictionary.ContainsKey(prevSymbol))
{
foreach (var targetState in TargetStatesDictionary[prevSymbol])
{
result.Add(newllconf.Push(targetState));
}
}
}
else
{
result.Add(llconf.Pop());
}
}
return(result);
}
public bool Subsumes(LlConfiguration <TSymbol> configuration)
{
if ((this.label.CompareTo(configuration.label) != 0) ||
this.stack.Count > configuration.Count())
{
return(false);
}
var firstStack = this.stack;
var secondStack = configuration.stack;
for (int i = 0; i < firstStack.Count; i++)
{
if (firstStack [firstStack.Count - i - 1] != secondStack[secondStack.Count - i - 1])
{
return(false);
}
}
return(true);
}
public bool Equals(LlConfiguration <TSymbol> other)
{
return(this.Subsumes(other) && other.Subsumes(this));
}
// Indexed by beginnings of terminal ranges.
public List <KeyValuePair <TSymbol, LlConfiguration <TSymbol> > > OutgoingTerminalEdges(LlConfiguration <TSymbol> llconf)
{
var topState = llconf.stack[llconf.stack.Count - 1];
var transitions = topState.Transitions;
var resultDict = new SortedDictionary <TSymbol, LlConfiguration <TSymbol> > ();
foreach (var kv in transitions)
{
var symbol = kv.Key;
var targetState = kv.Value;
// topState---symbol-->targetState (we pop topState and push targetState)
if (IsTerminal(symbol))
{
var newllconf = llconf.Pop(); // a copy without top state
newllconf = newllconf.Push(targetState);
resultDict.Add(symbol, newllconf);
}
}
var result = new List <KeyValuePair <TSymbol, LlConfiguration <TSymbol> > >();
foreach (var kv in resultDict)
{
result.Add(kv);
}
return(result);
}
