computeTargetState method

DFAState? computeTargetState(DFA dfa, DFAState previousD, int t)

Compute a target state for an edge in the DFA, and attempt to add the computed state and corresponding edge to the DFA.

@param dfa The DFA @param previousD The current DFA state @param t The next input symbol

@return The computed target DFA state for the given input symbol t. If t does not lead to a valid DFA state, this method returns {@link #ERROR}.

Implementation

DFAState? computeTargetState(DFA dfa, DFAState previousD, int t) {
  final reach = computeReachSet(previousD.configs, t, false);
  if (reach == null) {
    addDFAEdge(dfa, previousD, t, ATNSimulator.ERROR);
    return ATNSimulator.ERROR;
  }

  // create new target state; we'll add to DFA after it's complete
  DFAState? D = DFAState(configs: reach);

  final predictedAlt = getUniqueAlt(reach);

  if (debug) {
    final altSubSets =
        PredictionModeExtension.getConflictingAltSubsets(reach);
    log('SLL altSubSets=$altSubSets'
        ', configs=$reach'
        ', predict=$predictedAlt, allSubsetsConflict=${PredictionModeExtension.allSubsetsConflict(altSubSets)}, conflictingAlts=${getConflictingAlts(reach)}');
  }

  if (predictedAlt != ATN.INVALID_ALT_NUMBER) {
    // NO CONFLICT, UNIQUELY PREDICTED ALT
    D.isAcceptState = true;
    D.configs.uniqueAlt = predictedAlt;
    D.prediction = predictedAlt;
  } else if (PredictionModeExtension.hasSLLConflictTerminatingPrediction(
      predictionMode, reach)) {
    // MORE THAN ONE VIABLE ALTERNATIVE
    D.configs.conflictingAlts = getConflictingAlts(reach);
    D.requiresFullContext = true;
    // in SLL-only mode, we will stop at this state and return the minimum alt
    D.isAcceptState = true;
    D.prediction = D.configs.conflictingAlts!.nextset(0);
  }

  if (D.isAcceptState && D.configs.hasSemanticContext) {
    predicateDFAState(D, atn.getDecisionState(dfa.decision));
    if (D.predicates != null) {
      D.prediction = ATN.INVALID_ALT_NUMBER;
    }
  }

  // all adds to dfa are done after we've created full D state
  D = addDFAEdge(dfa, previousD, t, D);
  return D;
}