static ParseItemSet Closure(SegmentSetProvider provider, ParseItemSet kernelItems)
{
var lookup = new Dictionary <ParseItem, bool>();
var itemsToAdd = new Queue <ParseItem>();
EnqueueRange(itemsToAdd, kernelItems);
while (itemsToAdd.Count > 0)
{
var item = itemsToAdd.Dequeue();
var production = item.Production;
if (!lookup.ContainsKey(item))
{
lookup.Add(item, true);
if (item.Position < production.Segments.Length)
{
var next = production.Segments[item.Position];
if (!next.IsTerminal)
{
EnqueueRange(itemsToAdd, provider.CreateParseItems(next));
}
}
}
}
return(ParseItemSet.New(lookup.Keys));
}
static ParseGraph ConstructGraph(Config config, SegmentSetProvider provider)
{
var graphBuilder = new Graph.Builder();
var map = new Dictionary <ParseItemSet, Graph.State>();
var queue = new Queue <Graph.State>();
var startStates = new List <Graph.State>();
var topLevelSegments = new List <Segment>();
foreach (var segment in provider.InitialSegments)
{
var initialKernel = ParseItemSet.New(provider.CreateParseItems(segment));
var initialState = graphBuilder.NewState(true, Closure(provider, initialKernel));
map.Add(initialKernel, initialState);
queue.Enqueue(initialState);
startStates.Add(initialState);
topLevelSegments.Add(new Segment(segment.Name, false));
}
while (queue.Count > 0)
{
var fromState = queue.Dequeue();
foreach (var pair in fromState.Label.GetTransitionKernels())
{
if (!map.TryGetValue(pair.Value, out var toState))
{
toState = graphBuilder.NewState(false, Closure(provider, pair.Value));
map.Add(pair.Value, toState);
queue.Enqueue(toState);
}
graphBuilder.AddTransition(fromState, toState, pair.Key);
}
}
var graph = graphBuilder.Graph;
PopulateLookaheads(provider, graph);
ParseGraphOptimiser.Optimise(config, graphBuilder);
return(new ParseGraph(graph, topLevelSegments.ToArray(), startStates.ToArray()));
}
ParseItem[] FindTrivialItems(ParseItemSet set)
{
var count = set.Count;
var items = new ParseItem[count];
var tokens = new Segment[count];
var write = 0;
set.CopyTo(items, 0);
// Consider only incomplete items.
for (var i = 0; i < count; i++)
{
var item = items[i];
var production = item.Production;
if (item.Position < production.Segments.Length)
{
items[write] = items[i];
tokens[write] = production.Segments[item.Position];
write++;
}
}
if (write == 0)
{
return(null);
}
count = write;
write = 0;
Array.Sort(tokens, items, 0, count);
var duplicate = false;
var prevToken = tokens[0];
var prevItem = items[0];
// Discard items that share the "next" segment or have a non-trivial action.
for (var i = 1; i < count; i++)
{
var nextToken = tokens[i];
var nextItem = items[i];
if (nextToken == prevToken)
{
duplicate = true;
}
else
{
if (duplicate)
{
duplicate = false;
}
else if (!prevItem.Production.Target.IsInitial && _trivialLookup[prevItem.Production])
{
items[write] = prevItem;
tokens[write] = prevToken;
write++;
}
prevToken = nextToken;
prevItem = nextItem;
}
}
if (!duplicate && !prevItem.Production.Target.IsInitial && _trivialLookup[prevItem.Production])
{
items[write] = prevItem;
tokens[write] = prevToken;
write++;
}
if (write == 0)
{
return(null);
}
count = write;
if (count < items.Length)
{
Array.Resize(ref items, count);
}
return(items);
}