private DotState[] BuildLr0ItemSets()
{
var result = new List <DotState>();
var initialItemSet = ClosureLr0(new MutableDotItemSet
{
new DotItem(grammar.AugmentedProduction, 0)
{
LA = TokenSet.Mutable()
}
});
result.Add(new DotState(0, initialItemSet));
bool addedStatesInRound;
do
{
addedStatesInRound = false;
for (int i = 0; i != result.Count; ++i)
{
var itemSet = result[i].Items;
foreach (var token in GetOutTokens(itemSet))
{
var nextStateItems = GoTo(itemSet, token);
CollectClosureLookaheads(nextStateItems, grammar);
if (nextStateItems.Count == 0)
{
throw new InvalidOperationException("Internal error: next state cannot be empty");
}
var nextState = result.Find(state => state.Items.Equals(nextStateItems));
if (nextState == null)
{
addedStatesInRound = true;
nextState = new DotState(result.Count, nextStateItems);
result.Add(nextState);
}
if (result[i].AddTransition(token, nextState, TokenSet))
{
addedStatesInRound = true;
}
}
}
}while (addedStatesInRound);
StateSet = new BitSetType(result.Count);
return(result.ToArray());
}
public bool AddTransition(int token, DotState to, IntSetType tokenSetType)
{
bool result;
var existing = Transitions.FirstOrDefault(t => t.To == to);
if (existing == null)
{
existing = new DotTransition(tokenSetType.Mutable(), to);
Transitions.Add(existing);
result = true;
}
else
{
result = !existing.Tokens.Contains(token);
}
existing.Tokens.Add(token);
return(result);
}
private bool IsValueOnlyEpsilonReduceItem(DotItem item, DotState state, int lookahead)
{
if (item.Position != 0 ||
grammar.IsStartProduction(item.ProductionId) ||
!grammar.IsTailNullable(item) ||
!item.LA.Contains(lookahead))
{
return(false);
}
int epsilonToken = item.Outcome;
foreach (var parentItem in state.Items)
{
if (parentItem == item)
{
continue;
}
if (parentItem.NextToken == epsilonToken)
{
if (!grammar.IsTailNullable(parentItem))
{
// there is at least one rule which needs shift on epsilonToken
return(false);
}
if (grammar.HasFirst(parentItem.CreateNextItem(), lookahead))
{
// One of the subseqent non-terms in parentItem can start parsing with current lookahead.
// It means that we need tested epsilonToken production for continue parsing on parentItem.
return(false);
}
}
}
return(true);
}
public DotTransition(MutableIntSet tokens, DotState to)
{
this.Tokens = tokens;
this.To = to;
}