/// <summary>
/// Closes this item to a set of items
/// </summary>
/// <param name="closure">The list to close</param>
/// <param name="map">The current helper map</param>
public override void CloseTo(List <Item> closure, Dictionary <Rule, Dictionary <int, List <Item> > > map)
{
// the item was of the form [Var -> alpha .] (reduction)
// nothing to do
if (Action == LRActionCode.Reduce)
{
return;
}
// Get the next symbol in the item
Symbol next = GetNextSymbol();
// Here the item is of the form [Var -> alpha . next beta]
// If the next symbol is not a variable : do nothing
// If the next symbol is a variable :
Variable nextVar = next as Variable;
if (nextVar == null)
{
return;
}
// Firsts is a copy of the Firsts set for beta (next choice)
// Firsts will contains symbols that may follow Next
// Firsts will therefore be the lookahead for child items
TerminalSet firsts = new TerminalSet(GetNextChoice().Firsts);
// If beta is nullifiable (contains ε) :
if (firsts.Contains(Epsilon.Instance))
{
// Remove ε
firsts.Remove(Epsilon.Instance);
// Add the item's lookaheads
firsts.AddRange(lookaheads);
}
// For each rule that has Next as a head variable :
foreach (Rule rule in nextVar.Rules)
{
if (!map.ContainsKey(rule))
{
map.Add(rule, new Dictionary <int, List <Item> >());
}
Dictionary <int, List <Item> > sub = map[rule];
if (sub.ContainsKey(0))
{
List <Item> previouses = sub[0];
ItemLALR1 previous = previouses[0] as ItemLALR1;
previous.Lookaheads.AddRange(firsts);
}
else
{
List <Item> items = new List <Item>();
sub.Add(0, items);
ItemLALR1 New = new ItemLALR1(rule, 0, firsts);
closure.Add(New);
items.Add(New);
}
}
}