Examples of DFAState

org.antlr.v4.runtime.dfa.DFAState

A DFA state represents a set of possible ATN configurations. As Aho, Sethi, Ullman p. 117 says "The DFA uses its state to keep track of all possible states the ATN can be in after reading each input symbol. That is to say, after reading input a1a2..an, the DFA is in a state that represents the subset T of the states of the ATN that are reachable from the ATN's start state along some path labeled a1a2..an." In conventional NFA→DFA conversion, therefore, the subset T would be a bitset representing the set of states the ATN could be in. We need to track the alt predicted by each state as well, however. More importantly, we need to maintain a stack of states, tracking the closure operations as they jump from rule to rule, emulating rule invocations (method calls). I have to add a stack to simulate the proper lookahead sequences for the underlying LL grammar from which the ATN was derived.

I use a set of ATNConfig objects not simple states. An ATNConfig is both a state (ala normal conversion) and a RuleContext describing the chain of rules (if any) followed to arrive at that state.

A DFA state may have multiple references to a particular state, but with different ATN contexts (with same or different alts) meaning that state was reached via a different set of rule invocations.

    /* the lexer evaluates predicates on-the-fly; by this point configs
     * should not contain any configurations with unevaluated predicates.
     */
    assert !configs.hasSemanticContext;


    DFAState proposed = new DFAState(configs);
    ATNConfig firstConfigWithRuleStopState = null;
    for (ATNConfig c : configs) {
      if ( c.state instanceof RuleStopState )  {
        firstConfigWithRuleStopState = c;
        break;
      }
    }


    if ( firstConfigWithRuleStopState!=null ) {
      proposed.isAcceptState = true;
      proposed.lexerActionExecutor = ((LexerATNConfig)firstConfigWithRuleStopState).getLexerActionExecutor();
      proposed.prediction = atn.ruleToTokenType[firstConfigWithRuleStopState.state.ruleIndex];
    }


    DFA dfa = decisionToDFA[mode];
    synchronized (dfa.states) {
      DFAState existing = dfa.states.get(proposed);
      if ( existing!=null ) return existing;


      DFAState newState = proposed;


      newState.stateNumber = dfa.states.size();
      configs.setReadonly(true);
      newState.configs = configs;
      dfa.states.put(newState, newState);

    }


    for (DFAState d : dfa.states.keySet()) {
      if ( d.edges!=null ) {
        for (int i = 0; i < d.edges.length; i++) {
          DFAState target = d.edges[i];
          if ( target==null) continue;
          if ( target.stateNumber == Integer.MAX_VALUE ) continue;
          int ttype = i-1; // we shift up for EOF as -1 for parser
          String label = String.valueOf(ttype);
          if ( isLexer ) label = "'"+getEdgeLabel(String.valueOf((char) i))+"'";

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Examples of DFAState

Examples of org.antlr.v4.runtime.dfa.DFAState

Examples of org.antlr.v4.runtime.dfa.DFAState