public LRItemSet SelectByLookahead(Terminal lookahead)
{
var result = new LRItemSet();
foreach (var item in this)
{
if (item.Lookaheads.Contains(lookahead))
{
result.Add(item);
}
}
return(result);
}
public LRItemSet SelectByCurrent(BnfTerm current)
{
var result = new LRItemSet();
foreach (var item in this)
{
if (item.Core.Current == current)
{
result.Add(item);
}
}
return(result);
}
public LRItemSet SelectItemsWithNullableTails()
{
var result = new LRItemSet();
foreach (var item in this)
{
if (item.Core.TailIsNullable)
{
result.Add(item);
}
}
return(result);
}
public void AddItem(LR0Item core)
{
//Check if a core had been already added. If yes, simply return
if (!AllCores.Add(core))
{
return;
}
//Create new item, add it to AllItems, InitialItems, ReduceItems or ShiftItems
var item = new LRItem(State, core);
AllItems.Add(item);
if (item.Core.IsFinal)
{
ReduceItems.Add(item);
}
else
{
ShiftItems.Add(item);
}
if (item.Core.IsInitial)
{
InitialItems.Add(item);
}
if (core.IsFinal)
{
return;
}
//Add current term to ShiftTerms
if (!ShiftTerms.Add(core.Current))
{
return;
}
if (core.Current is Terminal)
{
ShiftTerminals.Add(core.Current as Terminal);
}
//If current term (core.Current) is a new non-terminal, expand it
var currNt = core.Current as NonTerminal;
if (currNt == null)
{
return;
}
foreach (var prod in currNt.Productions)
{
AddItem(prod.LR0Items[0]);
}
}//method
private LRItemSet SelectNewItemsThatNeedLookback(TransitionList transitions)
{
//Select items with nullable tails that don't have lookbacks yet
var items = new LRItemSet();
foreach (var trans in transitions)
{
foreach (var item in trans.Items)
{
if (item.Core.TailIsNullable && item.Lookbacks.Count == 0) //only if it does not have lookbacks yet
{
items.Add(item);
}
}
}
return(items);
}