// side-effect: can alter configs.hasSemanticContext
protected LexerATNConfig GetEpsilonTarget(ICharStream input,
LexerATNConfig config,
Transition t,
ATNConfigSet configs,
bool speculative,
bool treatEofAsEpsilon)
{
LexerATNConfig c = null;
switch (t.TransitionType)
{
case TransitionType.RULE:
RuleTransition ruleTransition = (RuleTransition)t;
PredictionContext newContext = new SingletonPredictionContext(config.context, ruleTransition.followState.stateNumber);
c = new LexerATNConfig(config, t.target, newContext);
break;
case TransitionType.PRECEDENCE:
throw new Exception("Precedence predicates are not supported in lexers.");
case TransitionType.PREDICATE:
/* Track traversing semantic predicates. If we traverse,
* we cannot add a DFA state for this "reach" computation
* because the DFA would not test the predicate again in the
* future. Rather than creating collections of semantic predicates
* like v3 and testing them on prediction, v4 will test them on the
* fly all the time using the ATN not the DFA. This is slower but
* semantically it's not used that often. One of the key elements to
* this predicate mechanism is not adding DFA states that see
* predicates immediately afterwards in the ATN. For example,
*
* a : ID {p1}? | ID {p2}? ;
*
* should create the start state for rule 'a' (to save start state
* competition), but should not create target of ID state. The
* collection of ATN states the following ID references includes
* states reached by traversing predicates. Since this is when we
* test them, we cannot cash the DFA state target of ID.
*/
PredicateTransition pt = (PredicateTransition)t;
if (debug)
{
ConsoleWriteLine("EVAL rule " + pt.ruleIndex + ":" + pt.predIndex);
}
configs.hasSemanticContext = true;
if (EvaluatePredicate(input, pt.ruleIndex, pt.predIndex, speculative))
{
c = new LexerATNConfig(config, t.target);
}
break;
case TransitionType.ACTION:
if (config.context == null || config.context.HasEmptyPath)
{
// execute actions anywhere in the start rule for a token.
//
// TODO: if the entry rule is invoked recursively, some
// actions may be executed during the recursive call. The
// problem can appear when hasEmptyPath() is true but
// isEmpty() is false. In this case, the config needs to be
// split into two contexts - one with just the empty path
// and another with everything but the empty path.
// Unfortunately, the current algorithm does not allow
// getEpsilonTarget to return two configurations, so
// additional modifications are needed before we can support
// the split operation.
LexerActionExecutor lexerActionExecutor = LexerActionExecutor.Append(config.getLexerActionExecutor(), atn.lexerActions[((ActionTransition)t).actionIndex]);
c = new LexerATNConfig(config, t.target, lexerActionExecutor);
break;
}
else
{
// ignore actions in referenced rules
c = new LexerATNConfig(config, t.target);
break;
}
case TransitionType.EPSILON:
c = new LexerATNConfig(config, t.target);
break;
case TransitionType.ATOM:
case TransitionType.RANGE:
case TransitionType.SET:
if (treatEofAsEpsilon)
{
if (t.Matches(IntStreamConstants.EOF, Lexer.MinCharValue, Lexer.MaxCharValue))
{
c = new LexerATNConfig(config, t.target);
break;
}
}
break;
}
return(c);
}