private bool AddClosureItems(ParserState state)
{
bool result = false;
for (int i = 0; i < state.Items.Count; i++)
{
LRItem item = state.Items[i];
NonTerminal nextNT = item.Core.NextElement as NonTerminal;
if (nextNT == null)
{
continue;
}
foreach (Production prod in nextNT.Productions)
{
LR0Item core = prod.LR0Items[0];
LRItem newItem = TryFindItem(state, core);
if (newItem == null)
{
newItem = new LRItem(state, core);
state.Items.Add(newItem);
result = true;
}
newItem.NewLookaheads.AddRange(item.Core.TailFirsts);
if (item.Core.TailIsNullable && !item.PropagateTargets.Contains(newItem))
{
item.PropagateTargets.Add(newItem);
}
}
}
return(result);
}
private LRItem TryFindItem(ParserState state, LR0Item core)
{
foreach (LRItem item in state.Items)
{
if (item.Core == core)
{
return(item);
}
}
return(null);
}
private void CalculateTailFirsts()
{
foreach (Production prod in _data.Productions)
{
StringSet accumulatedFirsts = new StringSet();
bool allNullable = true;
for (int i = prod.LR0Items.Count - 1; i >= 0; i--)
{
LR0Item item = prod.LR0Items[i];
if (i >= prod.LR0Items.Count - 2)
{
item.TailIsNullable = true;
item.TailFirsts.Clear();
continue;
}
GrammarTerm term = prod.RValues[item.Position + 1];
NonTerminal ntElem = term as NonTerminal;
if (ntElem == null || !ntElem.Nullable)
{
accumulatedFirsts.Clear();
allNullable = false;
item.TailIsNullable = false;
if (ntElem == null)
{
item.TailFirsts.Add(term.Key);
accumulatedFirsts.Add(term.Key);
}
else
{
item.TailFirsts.AddRange(ntElem.Firsts);
accumulatedFirsts.AddRange(ntElem.Firsts);
}
continue;
}
accumulatedFirsts.AddRange(ntElem.Firsts);
item.TailFirsts.AddRange(accumulatedFirsts);
item.TailIsNullable = allNullable;
}
}
}
private Dictionary <string, LR0ItemList> GetStateShifts(ParserState state)
{
Dictionary <string, LR0ItemList> shifts = new Dictionary <string, LR0ItemList>();
LR0ItemList list;
foreach (LRItem item in state.Items)
{
GrammarTerm term = item.Core.NextElement;
if (term == null)
{
continue;
}
LR0Item shiftedItem = item.Core.Production.LR0Items[item.Core.Position + 1];
if (!shifts.TryGetValue(term.Key, out list))
{
shifts[term.Key] = list = new LR0ItemList();
}
list.Add(shiftedItem);
}
return(shifts);
}
public LRItem(ParserState state, LR0Item core)
{
State = state;
Core = core;
}
public LRItem(ParserState state, LR0Item core)
{
State = state;
Core = core;
}
private LRItem TryFindItem(ParserState state, LR0Item core)
{
foreach (LRItem item in state.Items)
if (item.Core == core)
return item;
return null;
}
