public TransitionTable(Grammar grammar)
{
if (grammar == null)
throw new ArgumentNullException("grammar");
_table = new Dictionary<ParserState, Dictionary<GrammarSymbol, TransitionAction>>();
_grammar = grammar;
_stateMap = grammar.CreateStateMap();
ConstructTable();
}
/// <summary>
/// Create a map of the transitions out of each state based upon symbol inputs.
/// Refer Dragon Book pg 246
/// </summary>
/// <returns></returns>
public StateTransitionMap CreateStateMap()
{
var stateMap = new StateTransitionMap();
int currentStateNumber = 0;
//The first state is the closure of the starting symbol.
IList<ParserState> states = new List<ParserState>
{
new ParserState(currentStateNumber++, GetClosure(AugmentedState))
};
var grammarSymbols = Symbols;
//iterate through the states list.
// this list grows as we iterate
for (int i = 0; i < states.Count; i++)
{
var state = states[i];
foreach (var grammarSymbol in grammarSymbols)
{
//get the set of items to transition to for this input
var gotoForSymbol = Goto(state.Items, grammarSymbol);
//if the state exists
if (gotoForSymbol.Count > 0)
{
ParserState transitionTo;
if (!StateAlreadyExists(states, gotoForSymbol, out transitionTo))
{
//if there is not already a state with this set of items
// then create a new state with that set of items
// and add it to the states list
transitionTo = new ParserState(currentStateNumber++, gotoForSymbol);
states.Add(transitionTo);
}
//add the state transition from the current state
// to the state of the goto set.
// We do this here so that it is not necessary to
// calculate it again at a later stage.
stateMap.AddTransition(state, grammarSymbol, transitionTo);
}
}
}
return stateMap;
}
