//Check if there is an action already in state for this term; if yes, and it is Conditional action,
// then simply add an extra conditional entry to it. If an action does not exist, or it is not conditional,
// create new conditional action for this term.
private void AddConditionalEntry(ParserState state, BnfTerm term, ConditionalParserAction.ConditionalEntry entry)
{
ConditionalParserAction condAction = null;
if (state.Actions.TryGetValue(term, out ParserAction oldAction))
{
condAction = oldAction as ConditionalParserAction;
}
if (condAction == null) //there's no old action, or it is not conditional; create new conditional action
{
condAction = new ConditionalParserAction {
DefaultAction = oldAction
};
state.Actions[term] = condAction;
}
condAction.ConditionalEntries.Add(entry);
if (condAction.DefaultAction == null)
{
condAction.DefaultAction = FindDefaultAction(state, term);
}
if (condAction.DefaultAction == null)
{
//if still no action, then use the cond. action as default.
condAction.DefaultAction = entry.Action;
}
}
public override void Apply(LanguageData language, LRItem owner)
{
var state = owner.State;
if (!state.BuilderData.IsInadequate)
{
return; //the state is adequate, we don't need to do anything
}
var conflicts = state.BuilderData.Conflicts;
// Note that we remove lookaheads from the state conflicts set at the end of this method - to let parser builder know
// that this conflict is taken care of.
// On the other hand we may call this method multiple times for different LRItems if we have multiple hints in the same state.
// Since we remove lookahead from conflicts on the first call, on the consequitive calls it will not be a conflict -
// but we still need to add a new conditional entry to a conditional parser action for this lookahead.
// Thus we process the lookahead anyway, even if it is not a conflict.
// if (conflicts.Count == 0) return; -- this is a wrong thing to do
switch (_actionType)
{
case PreferredActionType.Reduce:
if (!owner.Core.IsFinal)
{
return;
}
//it is reduce action; find lookaheads in conflict
var lkhs = owner.Lookaheads;
if (lkhs.Count == 0)
{
return; //if no conflicts then nothing to do
}
var reduceAction = new ReduceParserAction(owner.Core.Production);
var reduceCondEntry = new ConditionalParserAction.ConditionalEntry(CheckCondition, reduceAction, _description);
foreach (var lkh in lkhs)
{
AddConditionalEntry(state, lkh, reduceCondEntry);
if (conflicts.Contains(lkh))
{
conflicts.Remove(lkh);
}
}
break;
case PreferredActionType.Shift:
var curr = owner.Core.Current as Terminal;
if (curr == null)
{
return; //it is either reduce item, or curr is a NonTerminal - we cannot shift it
}
var shiftAction = new ShiftParserAction(owner);
var shiftCondEntry = new ConditionalParserAction.ConditionalEntry(CheckCondition, shiftAction, _description);
AddConditionalEntry(state, curr, shiftCondEntry);
if (conflicts.Contains(curr))
{
conflicts.Remove(curr);
}
break;
default:
throw new ArgumentOutOfRangeException();
}
}
