/// <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>
/// Gets the LR(1) graph
/// </summary>
/// <returns>The corresponding LR(1) graph</returns>
private Graph GetGraphLR1()
{
// Create the first set
Variable axiom = grammar.GetVariable(Grammar.GENERATED_AXIOM);
ItemLR1 item = new ItemLR1(axiom.Rules[0], 0, Epsilon.Instance);
StateKernel kernel = new StateKernel();
kernel.AddItem(item);
State state0 = kernel.GetClosure();
Graph result = new Graph(state0);
// Construct the graph
foreach (State state in result.States)
{
state.BuildReductions(new StateReductionsLR1());
}
return(result);
}
/// <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 lookahead as possible symbol for firsts
firsts.Add(lookahead);
}
// 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))
{
sub.Add(0, new List <Item>());
}
List <Item> previouses = sub[0];
// For each symbol in Firsts : create the child with this symbol as lookahead
foreach (Terminal first in firsts)
{
// Child item creation and unique insertion
int sid = first.ID;
bool found = false;
foreach (Item previous in previouses)
{
if (previous.Lookaheads[0].ID == sid)
{
found = true;
break;
}
}
if (!found)
{
ItemLR1 New = new ItemLR1(rule, 0, first);
closure.Add(New);
previouses.Add(New);
}
}
}
}
/// <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)
{
ItemLR1 tested = item as ItemLR1;
return(lookahead.ID == tested.lookahead.ID && BaseEquals(tested));
}
