predTransition method

ATNConfig? predTransition(ATNConfig config, PredicateTransition pt, bool collectPredicates, bool inContext, bool fullCtx,)

Implementation

ATNConfig? predTransition(
  ATNConfig config,
  PredicateTransition pt,
  bool collectPredicates,
  bool inContext,
  bool fullCtx,
) {
  if (debug) {
    log('PRED (collectPredicates=$collectPredicates) '
        '${pt.ruleIndex}:${pt.predIndex}'
        ', ctx dependent=${pt.isCtxDependent}');

    log('context surrounding pred is ${parser.getRuleInvocationStack()}');
  }

  ATNConfig? c;
  if (collectPredicates &&
      (!pt.isCtxDependent || (pt.isCtxDependent && inContext))) {
    if (fullCtx) {
      // In full context mode, we can evaluate predicates on-the-fly
      // during closure, which dramatically reduces the size of
      // the config sets. It also obviates the need to test predicates
      // later during conflict resolution.
      final currentPosition = input.index;
      input.seek(startIndex);
      final predSucceeds = evalSemanticContextOne(
        pt.predicate,
        _outerContext,
        config.alt,
        fullCtx,
      );
      input.seek(currentPosition);
      if (predSucceeds) {
        c = ATNConfig.dup(config, state: pt.target); // no pred context
      }
    } else {
      final newSemCtx =
          SemanticContext.and(config.semanticContext, pt.predicate);
      c = ATNConfig.dup(config, state: pt.target, semanticContext: newSemCtx);
    }
  } else {
    c = ATNConfig.dup(config, state: pt.target);
  }

  if (debug) log('config from pred transition=$c');
  return c;
}