private static void PlaceReduceActions(GrammarCompilationContext context)
{
foreach (var state in context.States)
{
var finalizers = state.Items.Finalizers;
var finalizer = finalizers.FirstOrDefault();
if (finalizers.Count == state.Items.Count && finalizers.All(x => x.Kernel.Reduction == finalizer.Kernel.Reduction))
{
// State only has finalizers reducing to the same product.
state.State.DefaultAction = new ReduceParserAction(finalizer.Kernel.Reduction);
}
else
{
// Determine what reduce action to apply based on the lookaheads.
foreach (var item in finalizers)
{
foreach (var lookahead in item.Lookahead)
{
var reduceAction = new ReduceParserAction(item.Kernel.Reduction);
ParserAction action;
if (!state.State.Actions.TryGetValue(lookahead, out action))
{
state.State.Actions[lookahead] = reduceAction;
}
else
{
// State already handles the lookahead, introduce reduce conflict.
context.Conflicts.Add(new GrammarReductionConflict(
state.State,
lookahead,
action,
reduceAction));
}
}
}
}
}
}
public GrammarCompilationResult(GrammarCompilationContext context, ParserAutomaton automaton)
{
CompilationContext = context;
Automaton = automaton;
}
private static void CreateLr0States(GrammarCompilationContext context)
{
foreach (var augmentedRoot in context.GrammarData.AugmentedRoots)
{
var initialState = CreateInitialState(context, augmentedRoot);
context.InitialStates.Add(augmentedRoot, initialState);
// Don't replace this with a foreach loop. States are being added on the fly.
for (int i = 0; i < context.States.Count; i++)
ExpandState(context, context.States[i]);
ReplaceRootReductionWithAcceptance(augmentedRoot, initialState);
}
}
private static void ExpandState(GrammarCompilationContext context, IntermediateParserState state)
{
// Check for possible shifts.
foreach (var shifter in state.Items.Shifters)
{
var currentElement = shifter.Kernel.Element;
// Get all LR(1) items sharing the same grammar element, get or
// create the state that corresponds to the shifted items, and create
// a transition to that state.
var shiftedKernels = from item in state.Items
let kernel = item.Kernel
where kernel.Element == currentElement
select kernel.NextItem;
var kernelsArray = shiftedKernels.ToArray();
var nextState = context.GetOrCreateState(kernelsArray);
shifter.NextItem = nextState.Items.First(x => x.Kernel == shifter.Kernel.NextItem);
context.GetOrCreateTransition(state, currentElement, nextState);
if (!state.State.Actions.ContainsKey(currentElement))
{
var action = new ShiftParserAction(nextState.State);
var customActionElement = currentElement as CustomActionGrammarElement;
if (customActionElement != null)
action.CustomAction = customActionElement.Action;
state.State.Actions[currentElement] = action;
}
}
}
private static IntermediateParserState CreateInitialState(GrammarCompilationContext context, GrammarDefinition augmentedRoot)
{
// The initial state contains the very first LR(0) item, which is the augmented root '.Root'.
var initialItem = context.GrammarData.GrammarReductionsMapping[augmentedRoot][0].Lr0Items[0];
var initialState = context.GetOrCreateState(new [] { initialItem });
return initialState;
}
private static ParserAutomaton CreateAutomaton(GrammarCompilationContext context)
{
var automaton = new ParserAutomaton(context.GrammarData.Grammar);
foreach (var initialState in context.InitialStates)
automaton.InitialStates.Add((GrammarDefinition)initialState.Key.Rule.Switch[0][0], initialState.Value.State);
automaton.DefaultInitialState = context.InitialStates[context.GrammarData.DefaultAugmentedRoot].State;
automaton.States.AddRange(context.States.Select(x => x.State));
return automaton;
}
private static void ConstructAugmentedGrammar(GrammarCompilationContext context)
{
// Augmented grammar is constructed as described in page 197 of
// http://web.stanford.edu/class/archive/cs/cs143/cs143.1128/lectures/06/Slides06.pdf
foreach (var state in context.States)
{
foreach (var item in state.Items)
{
if (!item.Kernel.IsInitializer)
continue;
var reduction = new AugmentedGrammarReduction()
{
Product = context.GetOrCreateAnnotatedElement(item.Kernel.Reduction.Product,
state.OutgoingTransitions.GetOrDefault(item.Kernel.Reduction.Product)),
Reduction = item.Kernel.Reduction
};
for (var currentItem = item; !currentItem.Kernel.IsFinalizer; currentItem = currentItem.NextItem)
{
var element = currentItem.Kernel.Element;
ParserTransition transition = null;
var definition = element as GrammarDefinition;
if (definition != null)
transition = currentItem.State.OutgoingTransitions.GetOrDefault(element);
var annotatedElement = context.GetOrCreateAnnotatedElement(element, transition);
annotatedElement.Parents.Add(reduction);
reduction.Sequence.Add(annotatedElement);
}
}
}
}
private static void ComputeLookaheads(GrammarCompilationContext context)
{
foreach (var state in context.States)
{
foreach (var item in state.Items)
{
if (!item.Kernel.IsInitializer)
continue;
var finalizer = item.GetFinalizer();
if (finalizer.State.Items.Count == 1)
continue;
var annotatedElement = context.GetAnnotatedGrammarElement(item.Kernel.Reduction.Product, state);
if (annotatedElement!= null)
finalizer.Lookahead.UnionWith(annotatedElement.GetFollowSet());
}
}
}
public static GrammarCompilationResult Compile(GrammarData grammarData)
{
if (grammarData == null)
throw new ArgumentNullException(nameof(grammarData));
var context = new GrammarCompilationContext(grammarData);
CreateLr0States(context);
ConstructAugmentedGrammar(context);
ComputeLookaheads(context);
PlaceReduceActions(context);
var automaton = CreateAutomaton(context);
var result = new GrammarCompilationResult(context, automaton);
return result;
}
