/// <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);
}
}
}
/// <summary>
/// Builds the propagation table
/// </summary>
/// <remarks>
/// The propagation table is a couple of list where
/// items in the first list propagate to items in the second list at the same index
/// </remarks>
private void BuildPropagationTable()
{
for (int i = 0; i != kernels.Count; i++)
{
StateKernel kernelLALR1 = kernels[i];
State stateLR0 = graphLR0.States[i];
// For each LALR(1) item in the kernel
// Only the kernel needs to be examined as the other items will be discovered and treated
// with the dummy closures
foreach (ItemLALR1 itemLALR1 in kernelLALR1.Items)
{
// If ItemLALR1 is of the form [A -> alpha .]
// => The closure will only contain the item itself
// => Cannot be used to generate or propagate lookaheads
if (itemLALR1.Action == LRActionCode.Reduce)
{
continue;
}
// Item here is of the form [A -> alpha . beta]
// Create the corresponding dummy item : [A -> alpha . beta, dummy]
// This item is used to detect lookahead propagation
ItemLR1 dummyItem = new ItemLR1(itemLALR1.BaseRule, itemLALR1.DotPosition, Dummy.Instance);
StateKernel dummyKernel = new StateKernel();
dummyKernel.AddItem(dummyItem);
State dummySet = dummyKernel.GetClosure();
// For each item in the closure of the dummy item
foreach (ItemLR1 item in dummySet.Items)
{
// If the item action is a reduction
// => OnSymbol for this item will be created by the LALR(1) closure
// => Do nothing
if (item.Action == LRActionCode.Reduce)
{
continue;
}
// Get the child item in the child LALR(1) kernel
State childLR0 = stateLR0.GetChildBy(item.GetNextSymbol());
StateKernel childKernel = kernels[childLR0.ID];
ItemLALR1 childLALR1 = (ItemLALR1)GetEquivalentInSet(childKernel, item.GetChild());
// If the lookaheads of the item in the dummy set contains the dummy terminal
if (item.Lookahead == Dummy.Instance)
{
// => Propagation from the parent item to the child
propagOrigins.Add(itemLALR1);
propagTargets.Add(childLALR1);
}
else
{
// => Spontaneous generation of lookaheads
childLALR1.Lookaheads.Add(item.Lookahead);
}
}
}
}
}
/// <summary>
/// Builds the kernels
/// </summary>
private void BuildKernels()
{
for (int i = 0; i != graphLR0.States.Count; i++)
{
State stateLR0 = graphLR0.States[i];
StateKernel kernelLALR1 = new StateKernel();
foreach (Item itemLR0 in stateLR0.Kernel.Items)
{
ItemLALR1 itemLALR1 = new ItemLALR1(itemLR0);
if (i == 0)
{
itemLALR1.Lookaheads.Add(Epsilon.Instance);
}
kernelLALR1.AddItem(itemLALR1);
}
kernels.Add(kernelLALR1);
}
}
/// <summary>
/// Determines whether the specified <see cref="Hime.SDK.Grammars.LR.Item"/> is equal to the current <see cref="Hime.SDK.Grammars.LR.Item"/>.
/// </summary>
/// <param name='item'>
/// The <see cref="Hime.SDK.Grammars.LR.Item"/> to compare with the current <see cref="Hime.SDK.Grammars.LR.Item"/>.
/// </param>
/// <returns>
/// <c>true</c> if the specified <see cref="Hime.SDK.Grammars.LR.Item"/> is equal to the current
/// <see cref="Hime.SDK.Grammars.LR.Item"/>; otherwise, <c>false</c>.
/// </returns>
public override bool ItemEquals(Item item)
{
ItemLALR1 tested = (ItemLALR1)item;
if (!BaseEquals(tested))
{
return(false);
}
if (lookaheads.Count != tested.lookaheads.Count)
{
return(false);
}
foreach (Terminal terminal in lookaheads)
{
if (!tested.lookaheads.Contains(terminal))
{
return(false);
}
}
return(true);
}
