/// <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>
/// 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>
/// Builds the given parent graph
/// </summary>
/// <param name="graph">The parent graph</param>
public void BuildGraph(Graph graph)
{
// Shift dictionnary for the current set
Dictionary <Symbol, StateKernel> shifts = new Dictionary <Symbol, StateKernel>();
// Build the children kernels from the shift actions
foreach (Item item in items)
{
// Ignore reduce actions
if (item.Action == LRActionCode.Reduce)
{
continue;
}
Symbol next = item.GetNextSymbol();
if (shifts.ContainsKey(next))
{
shifts[next].AddItem(item.GetChild());
}
else
{
StateKernel nextKernel = new StateKernel();
nextKernel.AddItem(item.GetChild());
shifts.Add(next, nextKernel);
}
}
// Close the children and add them to the graph
foreach (Symbol next in shifts.Keys)
{
StateKernel nextKernel = shifts[next];
State child = graph.ContainsState(nextKernel);
if (child == null)
{
child = nextKernel.GetClosure();
graph.Add(child);
}
children.Add(next, child);
}
// Build the context data
foreach (Item item in items)
{
if (item.BaseRule.Context != 0 && item.DotPosition == 0 && item.Action == LRActionCode.Shift)
{
// this is the opening of a context
List <Terminal> openingTerminals = new List <Terminal>();
Symbol first = item.GetNextSymbol();
if (first is Terminal)
{
openingTerminals.Add(first as Terminal);
}
else
{
openingTerminals.AddRange((first as Variable).Firsts);
}
foreach (Terminal terminal in openingTerminals)
{
List <int> contexts;
if (openingContexts.ContainsKey(terminal))
{
contexts = openingContexts[terminal];
}
else
{
contexts = new List <int>();
openingContexts.Add(terminal, contexts);
}
if (!contexts.Contains(item.BaseRule.Context))
{
contexts.Add(item.BaseRule.Context);
}
}
}
}
}
