//TODO: need to rewrite, looks ugly
private bool Recover()
{
//for recovery the current token must be error token, we rely on it
if (!_currentToken.IsError())
{
_currentToken = _context.CreateErrorToken(_currentToken.Location, _currentToken.Text);
}
//Check the current state and states in stack for error shift action - this would be recovery state.
ActionRecord action = GetCurrentAction();
if (action == null || action.ActionType == ParserActionType.Reduce)
{
while (Stack.Count > 0)
{
_currentState = Stack.Top.State;
Stack.Pop(1);
action = GetCurrentAction();
if (action != null && action.ActionType != ParserActionType.Reduce)
{
break; //we found shift action for error token
}
}//while
}//if
if (action == null || action.ActionType == ParserActionType.Reduce)
{
return(false); //could not find shift action, cannot recover
}
//We found recovery state, and action contains ActionRecord for "error shift". Lets shift it.
ExecuteShiftAction(action);//push the error token
// Now shift all tokens from input that can be shifted.
// These are the ones that are found in error production after the error. We ignore all other tokens
// We stop when we find a state with reduce-only action.
while (_currentToken.Terminal != Grammar.Eof)
{
//with current token, see if we can shift it.
action = GetCurrentAction();
if (action == null)
{
NextToken(); //skip this token and continue reading input
continue;
}
if (action.ActionType == ParserActionType.Reduce || action.ActionType == ParserActionType.Operator)
{
//we can reduce - let's reduce and return success - we recovered.
ExecuteReduceAction(action);
return(true);
}
//it is shift action, let's shift
ExecuteShiftAction(action);
}//while
return(false); //
}