private void PerformPanicRecovery(Lexeme z, List <ParserHead> shiftedHeads)
{
//Panic recovery
//to the 1st head:
//pop stack until there's a state S, which has a Goto action of a non-terminal A
//discard input until there's an token a in Follow(A)
//push Goto(s, A) into stack
//discard all other heads
m_heads.Clear();
m_heads.AddRange(shiftedHeads.Where(h => h.ErrorRecoverLevel == 0));
shiftedHeads.Clear();
ParserHead errorHead1 = m_errorCandidates[0];
m_errorCandidates.Clear();
IProduction p = errorHead1.PanicRecover(m_transitions, z.Value.Span, z.IsEndOfStream);
ProductionBase productionBase = p as ProductionBase;
if (productionBase != null)
{
var follow = productionBase.Info.Follow;
m_heads.Add(errorHead1);
throw new PanicRecoverException(follow);
}
}
private void PerformPanicRecovery(Lexeme z, List <ParserHead> shiftedHeads)
{
//Panic recovery
//to the 1st head:
//pop stack until there's a state S, which has a Goto action of a non-terminal A
//discard input until there's an token a in Follow(A)
//push Goto(s, A) into stack
//discard all other heads
m_heads.Clear();
m_heads.AddRange(shiftedHeads.Where(h => h.ErrorRecoverLevel == 0));
shiftedHeads.Clear();
ParserHead errorHead1 = m_errorCandidates[0];
m_errorCandidates.Clear();
var candidates = errorHead1.PanicRecover(m_transitions, z.Value.Span, z.IsEndOfStream);
ISet <IProduction> follows = new HashSet <IProduction>();
foreach (var candidate in candidates)
{
ProductionBase p = candidate.Item2 as ProductionBase;
follows.UnionWith(p.Info.Follow);
m_heads.Add(candidate.Item1);
}
if (m_heads.Count > 0)
{
throw new PanicRecoverException(follows);
}
else
{
throw new ParsingFailureException("There's no way to recover from parser error");
}
}
private void RecoverError(Lexeme z)
{
List <ParserHead> shiftedHeads = m_shiftedHeads;
m_heads.Clear();
int errorHeadCount = m_errorCandidates.Count;
Debug.Assert(errorHeadCount > 0);
if (errorHeadCount > c_panicRecoveryThreshold)
{
//Panic recovery
//to the 1st head:
//pop stack until there's a state S, which has a Goto action of a non-terminal A
//discard input until there's an token a in Follow(A)
//push Goto(s, A) into stack
//discard all other heads
m_heads.Clear();
m_heads.AddRange(shiftedHeads.Where(h => h.ErrorRecoverLevel == 0));
shiftedHeads.Clear();
ParserHead errorHead1 = m_errorCandidates[0];
m_errorCandidates.Clear();
IProduction p = errorHead1.PanicRecover(m_transitions, z.Value.Span);
var follow = (p as ProductionBase).Info.Follow;
m_heads.Add(errorHead1);
throw new PanicRecoverException(follow);
}
for (int i = 0; i < errorHeadCount; i++)
{
var head = m_errorCandidates[i];
if (!z.IsEndOfStream)
{
//option 1: remove
//remove current token and continue
var deleteHead = head.Clone();
deleteHead.IncreaseErrorRecoverLevel();
deleteHead.AddError(new ErrorRecord(m_errorDef.TokenUnexpectedId, z.Value.Span)
{
ErrorArgument = z.Value
});
shiftedHeads.Add(deleteHead);
//option 2: replace
//replace the current input char with all possible shifts token and continue
ReduceAndShiftForRecovery(z, head, shiftedHeads, m_errorDef.TokenMistakeId);
}
//option 3: insert
//insert all possible shifts token and continue
ReduceAndShiftForRecovery(z, head, m_heads, m_errorDef.TokenMissingId);
}
}