Hi Cliff,
I reported this same problem on February 10 on this list. It's an Antlr
bug, and my emails on it had the work around (which requires you to
implement a custom superclass if you haven't already). If you search the
list archives you should be able to find it.
Ron
Cliff Hudson wrote:
> I have been trying to work through an issue with an infinite loop caused
> when no tokens can be matched because a predicate has failed its test. The
> problem appears to be in the Lexer.NextToken() (looking at CSharp2 sources)
> method, which I have copied here for reference:
>
> /// <summary>
> /// Return a token from this source; i.e., Match a token on the
> char stream.
> /// </summary>
> public virtual IToken NextToken()
> {
> while (true)
> {
> state.token = null;
> state.channel = Token.DEFAULT_CHANNEL;
> state.tokenStartCharIndex = input.Index;
> state.tokenStartCharPositionInLine =
> input.CharPositionInLine;
> state.tokenStartLine = input.Line;
> state.text = null;
> if (input.LA(1) == (int)CharStreamConstants.EOF)
> {
> return Token.EOF_TOKEN;
> }
> try
> {
> mTokens();
> if (state.token == null)
> {
> Emit();
> }
> else if (state.token ==
> Token.SKIP_TOKEN)
> {
> continue;
> }
> return state.token;
> }
> catch (NoViableAltException nva) {
> ReportError(nva);
> Recover(nva); // throw out current char
> and try again
> }
> catch (RecognitionException re) {
> ReportError(re);
> // Match() routine has already called
> Recover()
> }
> }
> }
>
> Note the RecognitionException clause. This is the clause which will
> catch the FailedPredicateException(). Unfortunately, because the
> FailedPredicateException gets thrown just before Match() occurs in the
> rule, Recover will *not* have been called by the rule or its callees,
> and therefore the DFA will continue to try processing the same token.
> It would appear that there should instead be a specific
> FailedPredicateException clause which does the same thing as the
> NoViableAltException clause.
>
> I have seen two other people ask questions about this error, and in
> neither case was a suitable response given. Has this bug been fixed
> in non-released builds? Can someone give me an up-or-down on whether
> this is a correct and appropriate fix?
>
> Thanks.
>
> - Cliff
>
> List: http://www.antlr.org/mailman/listinfo/antlr-interest
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>
>
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Ron Hunter-Duvar | Software Developer V | 403-272-6580
Oracle Service Engineering
Gulf Canada Square 401 - 9th Avenue S.W., Calgary, AB, Canada T2P 3C5
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