protected bool TryRecoverFromError(ParsingContext context)
{
var grammar = context.Language.Grammar;
var parser = context.Parser;
//1. We need to find a state in the stack that has a shift item based on error production (with error token),
// and error terminal is current. This state would have a shift action on error token.
ParserAction errorShiftAction = FindErrorShiftActionInStack(context);
if (errorShiftAction == null)
{
return(false); //we failed to recover
}
context.AddTrace(Resources.MsgTraceRecoverFoundState, context.CurrentParserState);
//2. Shift error token - execute shift action
context.AddTrace(Resources.MsgTraceRecoverShiftError, errorShiftAction);
errorShiftAction.Execute(context);
//4. Now we need to go along error production until the end, shifting tokens that CAN be shifted and ignoring others.
// We shift until we can reduce
context.AddTrace(Resources.MsgTraceRecoverShiftTillEnd);
while (true)
{
if (context.CurrentParserInput == null)
{
parser.ReadInput();
}
if (context.CurrentParserInput.Term == grammar.Eof)
{
return(false);
}
//Check if we can reduce
var nextAction = parser.GetNextAction();
if (nextAction == null)
{
parser.ReadInput();
continue;
}
if (nextAction is ReduceParserAction)
{
//We are reducing a fragment containing error - this is the end of recovery
//Clear all input token queues and buffered input, reset location back to input position token queues;
context.SetSourceLocation(context.CurrentParserInput.Span.Location);
//Reduce error production - it creates parent non-terminal that "hides" error inside
context.AddTrace(Resources.MsgTraceRecoverReducing);
context.AddTrace(Resources.MsgTraceRecoverAction, nextAction);
nextAction.Execute(context); //execute reduce
return(true); //we recovered
}
// If it is not reduce, simply execute it (it is most likely shift)
context.AddTrace(Resources.MsgTraceRecoverAction, nextAction);
nextAction.Execute(context); //shift input token
}
}//method
