[antlr-interest] Bug in exception initialization code?

Søren Boisen sboisen at mail.dk
Mon Mar 28 07:35:23 PDT 2011


Hi Michael,

Thanks for the reply. I agree that it was due to an error in my tree walker
grammar (that I've now found and fixed), but I think it is pretty bad that
ANTLR generates an internal error with no useful information, whenever I
make a mistake in my grammar. It certainly doesn't make it easy to learn
ANTLR and how to create tree parsers :-)

I was therefore hoping for Ter or someone else with access, to create an
issue in the bug tracker, so it could be solved eventually.

Regards
Søren

2011/3/28 Michael Bedward <michael.bedward at gmail.com>

> Hi Søren,
>
> I see that error every so often and, so far al least, it has always
> been due to an error in my tree walker grammar - specifically an
> alternative that arises in the AST but that I forgot to consider in
> the grammar.
>
> Michael
>
> On 28 March 2011 23:29, Søren Boisen <sboisen at mail.dk> wrote:
> > Greetings,
> > I have a encountered a problem while trying to write a tree parser for my
> > grammar. Sometimes when trying to walk the AST and the tree parser fails
> to
> > match some input, I get the following exception:
> >
> > can't look backwards more than one token in this stream
> >    org.antlr.runtime.misc.LookaheadStream.LB(LookaheadStream.java:159)
> >    org.antlr.runtime.misc.LookaheadStream.LT(LookaheadStream.java:120)
> >
> >
> org.antlr.runtime.RecognitionException.extractInformationFromTreeNodeStream(RecognitionException.java:144)
> >    org.antlr.runtime.RecognitionException.(RecognitionException.java:111)
> >
> >
> org.antlr.runtime.MismatchedTreeNodeException.(MismatchedTreeNodeException.java:42)
> >
> >
> org.antlr.runtime.tree.TreeParser.recoverFromMismatchedToken(TreeParser.java:135)
> >    org.antlr.runtime.BaseRecognizer.match(BaseRecognizer.java:115)
> >
> >
> com.brunata.ws.rest.odata.query.NearestTelegramQueryWalker.queryOp(NearestTelegramQueryWalker.java:243)
> >
> >
> com.brunata.ws.rest.odata.query.NearestTelegramQueryWalker.stmt(NearestTelegramQueryWalker.java:128)
> >
> > I have looked through the FAQ, the issue tracker and Google, but I
> couldn't
> > find anything that looked related.
> >
> > From the stack trace it looks like an error in the
> > extractInformationFromTreeNodeStream, since I guess it shouldn't expect
> to
> > always be able to look back more than one token in a stream.
> > Is there a workaround for this? This is the code I use for creating
> parsers
> > and streams:
> >
> >        String query = ...;  // this is a parameter to the method
> >        Map<String, String> propertyFilters = ...; // this is a field on
> the
> > class
> >
> >        ANTLRStringStream input = new ANTLRStringStream(query);
> >        QueryParserLexer lexer = new QueryParserLexer(input);
> >
> >        CommonTokenStream tokens = new CommonTokenStream(lexer);
> >        QueryParserParser parser = new QueryParserParser(tokens);
> >
> >        QueryParserParser.stmt_return result = tryParse(parser, query);
> >        ast = (CommonTree) result.getTree();
> >
> >        CommonTreeNodeStream nodes = new CommonTreeNodeStream(ast);
> >        nodes.setTokenStream(tokens);
> >
> >        NearestTelegramQueryWalker walker = new
> > NearestTelegramQueryWalker(nodes);
> >        propertyFilters = tryWalk(walker, query);
> >
> > Am I using the wrong kind of token/node streams or something?
> >
> > Regards,
> > Søren Boisen
> >
> > List: http://www.antlr.org/mailman/listinfo/antlr-interest
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> >
>


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