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
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