private ParserAction GetShiftActionInCurrentState()
{
ParserAction result = null;
if (_currentState.Actions.TryGetValue(_currentInput.Term, out result) ||
_currentInput.Token != null && _currentInput.Token.AsSymbol != null &&
_currentState.Actions.TryGetValue(_currentInput.Token.AsSymbol, out result))
{
if (result.ActionType == ParserActionType.Shift)
{
return(result);
}
}
return(null);
}
private bool TryRecoverImpl()
{
//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();
if (errorShiftAction == null)
{
return(false); //we failed to recover
}
//2. Shift error token - execute shift action
if (_traceOn)
{
AddTraceEntry();
}
ExecuteShift(errorShiftAction.NewState);
//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
while (_currentInput.Term != _grammar.Eof)
{
//Check if we can reduce
var action = GetReduceActionInCurrentState();
if (action != null)
{
//Now reset scanner's position to current input position and clear all token queues; do it before ExecuteReduce
// as reset would clear the input stack
ResetSourceLocation(_currentInput.Span.Start, _currentInput.Span.EndPos);
ExecuteReduce(action.ReduceProduction);
return(true); //we recovered
}
//No reduce action in current state. Try to shift current token or throw it away or reduce
action = GetShiftActionInCurrentState();
if (action != null)
{
ExecuteShift(action.NewState); //shift input token
}
else
{
ReadInput(); //throw away input token
}
}
return(false);
}//method
private bool ExecuteAction()
{
if (_currentInput == null)
{
ReadInput();
}
//Trace current state if tracing is on
if (_traceOn)
{
_currentTraceEntry = _context.AddParserTrace(_currentState, Stack.Top, _currentInput);
}
//Try getting action
ParserAction action = GetAction();
if (action == null)
{
ReportParseError();
return(TryRecover());
}
//write trace
if (_currentTraceEntry != null)
{
_currentTraceEntry.SetDetails(action.ToString(), _currentState);
}
//Execute it
switch (action.ActionType)
{
case ParserActionType.Shift: ExecuteShift(action.NewState); break;
case ParserActionType.Operator: ExecuteOperatorAction(action.NewState, action.ReduceProduction); break;
case ParserActionType.Reduce: ExecuteReduce(action.ReduceProduction); break;
case ParserActionType.Code: ExecuteConflictAction(action); break;
case ParserActionType.Jump: ExecuteNonCanonicalJump(action); break;
case ParserActionType.Accept: ExecuteAccept(action); return(false);
}
//add info to trace
return(true);
}
private void ExecuteConflictAction(ParserAction action)
{
var args = new ConflictResolutionArgs(_context, action);
_grammar.OnResolvingConflict(args);
switch (args.Result)
{
case ParserActionType.Reduce:
ExecuteReduce(args.ReduceProduction);
break;
case ParserActionType.Operator:
ExecuteOperatorAction(action.NewState, args.ReduceProduction);
break;
case ParserActionType.Shift:
default:
ExecuteShift(action.NewState);
break;
}
}
private void ExecuteNonCanonicalJump(ParserAction action)
{
_currentState = action.NewState;
}
public static ParserAction CreateCodeAction(ParserState newState, Production reduceProduction)
{
var action = new ParserAction(ParserActionType.Code, newState, reduceProduction);
return(action);
}