private bool TryResolveConflictByHints(ParserState state, BnfTerm conflict)
{
var stateData = state.BuilderData;
//reduce hints
var reduceItems = stateData.ReduceItems.SelectByLookahead(conflict);
foreach (var reduceItem in reduceItems)
{
if (reduceItem.Core.Hints != null)
{
foreach (var hint in reduceItem.Core.Hints)
{
if (hint.HintType == HintType.ResolveToReduce)
{
var newAction = ParserAction.CreateReduce(reduceItem.Core.Production);
state.Actions[conflict] = newAction; //replace/add reduce action
return(true);
}
}
}
}
//Shift hints
var shiftItems = stateData.ShiftItems.SelectByCurrent(conflict);
foreach (var shiftItem in shiftItems)
{
if (shiftItem.Core.Hints != null)
{
foreach (var hint in shiftItem.Core.Hints)
{
if (hint.HintType == HintType.ResolveToShift)
{
//shift action is already there
return(true);
}
}
}
}
//code hints
// first prepare data for conflict action: reduceProduction (for possible reduce) and newState (for possible shift)
var reduceProduction = reduceItems.First().Core.Production; //take first of reduce productions
ParserState newState = (state.Actions.ContainsKey(conflict) ? state.Actions[conflict].NewState : null);
// Get all items that might contain hints; first take all shift items and reduce items in conflict;
// we should also add lookahead sources of reduce items. Lookahead source is an LR item that produces the lookahead,
// so if it contains a code hint right before the lookahead term, then it applies to this conflict as well.
var allItems = new LRItemList();
allItems.AddRange(shiftItems);
foreach (var reduceItem in reduceItems)
{
allItems.Add(reduceItem);
allItems.AddRange(reduceItem.ReducedLookaheadSources);
}
// Scan all items and try to find hint with resolution type Code
foreach (var item in allItems)
{
if (item.Core.Hints != null)
{
foreach (var hint in item.Core.Hints)
{
if (hint.HintType == HintType.ResolveInCode)
{
//found hint with resolution type "code" - this is instruction to use custom code here to resolve the conflict
// create new ConflictAction and place it into Actions table
var newAction = ParserAction.CreateCodeAction(newState, reduceProduction);
state.Actions[conflict] = newAction; //replace/add reduce action
return(true);
}
}
}
}
return(false);
}