private HashSet <uint> FindFirst(Grammar grammar, uint symbolIndex)
{
var set = _terminalSets[symbolIndex];
if (set == null)
{
set = _terminalSets[symbolIndex] = new HashSet <uint>();
foreach (var rule in grammar.Where(x => x.Left.Id == symbolIndex))
{
if (rule.IsEpsilon)
{
set.Add(0);
}
else
{
foreach (var symbol in rule.Right)
{
if (symbol.Id != symbolIndex)
{
var rightSet = FindFirst(grammar, symbol.Id);
set.UnionWith(rightSet);
if (!rightSet.Contains(0))
{
break;
}
}
}
}
}
}
return(set);
}
public State Closure(Grammar grammar)
{
var queue = new Queue <LR1Item>(this);
while (queue.Count > 0)
{
var item = queue.Dequeue();
var currentRule = item.Production;
var pos = item.Position;
if (pos >= currentRule.Right.Length)
{
continue;
}
var B = currentRule.Right[pos];
if (B.IsTerminal)
{
continue;
}
//else if (grammar.TerminalSets.HasEmpty(B.Id))
//{
// var newItem = new LR1Item(item.Production, pos + 1, item.Lookahead);
// if (Add(newItem))
// queue.Enqueue(newItem);
//}
var firstSet = currentRule.FindFirst(pos + 1, item.Lookahead);
foreach (var production in grammar.Where(x => x.Left == B))
{
foreach (var term in firstSet)
{
var newItem = new LR1Item(production, 0, grammar.Symbols[(int)term]);
if (Add(newItem))
{
queue.Enqueue(newItem);
}
}
}
}
return(this);
}
