/// <summary>
/// Compute the collection of Lr states by recursively applying productions from root state until no new states are added.
/// </summary>
private void CreateLrItemsAndStates()
{
var rootProduction = Grammar.Productions[0];
var rootItem = LrItems.GetOrAdd(rootProduction, 0, 1);
var rootState = LrStates.GetOrAdd(ComputeClosure(new SortedSet <LrItem> {
rootItem
}));
var open = new Queue <LrState>();
open.Enqueue(rootState);
while (open.Count > 0)
{
var state = open.Dequeue();
var gotos = new LrState[Grammar.Tokens.Length];
var gotoPrecedences = new ushort?[Grammar.Tokens.Length];
foreach (var token in Enumerable.Range(0, Grammar.Tokens.Length))
{
bool bAdded;
ushort?precedence;
var gotoState = GotoLr(state, token, out bAdded, out precedence);
gotos[token] = gotoState;
gotoPrecedences[token] = precedence;
if (bAdded)
{
open.Enqueue(gotoState);
}
}
state.Gotos = gotos;
state.GotoPrecedences = gotoPrecedences;
}
}
/// <summary>
/// Given the set of items in state, calculate for each token the closed set of items that can result from processing said token.
/// </summary>
/// <param name="state">The staring state.</param>
/// <param name="token">The token to process.</param>
/// <param name="bAdded">Return true if new state was added.</param>
/// <param name="precedence">Return the precedence of the goto.</param>
/// <returns>Returns the resulting LrState or null of unable to process the specified token on any of the state items.</returns>
private LrState GotoLr(LrState state, int token, out bool bAdded, out ushort?precedence)
{
ushort?prec = null;
var targetItems = new SortedSet <LrItem>();
foreach (var item in state.Items)
{
if (item.CanIncrement && (item.NextToken == token))
{
var newItem = LrItems.GetOrAdd(item.Production, item.ProductionProgress + 1, item.LookAheadSymbol);
targetItems.Add(newItem);
if (!prec.HasValue)
{
prec = item.Production.Precedence;
}
else if (item.Production.Precedence > prec)
{
prec = item.Production.Precedence;
}
}
}
if (targetItems.Count == 0)
{
bAdded = false;
precedence = null;
return(null);
}
var targetItemsWithClosure = ComputeClosure(targetItems);
var targetState = LrStates.GetOrAdd(targetItemsWithClosure, out bAdded);
precedence = prec;
return(targetState);
}
