[antlr-interest] Help with null tree?

Kim Slattery slattery.kim at gmail.com
Tue Apr 19 08:30:50 PDT 2011


Hi, all.  I've been working on translating the language our lab has created
(Hop) to Java, and I keep hitting a wall. Has anyone had experience with the
StringTemplate returned by getTemplate() being null?  When I debug, st
inside the tree returned by the tree grammar is null, and I can't figure out
why.  Is this because there's something wrong with the template?  Any
guesses?

I'm referring to code that, from Dr. Parr's books, looks like:

Gen.prog_return r2 = walker.prog(parser.numOps, parser.locals);

Above, the st in the start_return (or prog_return, or what is returned by
the start rule) of r2 is null.  And:

StringTemplate output = (StringTemplate)r2.getTemplate();
System.out.println(output.toString());

Because st is null, the output is obviously null.  My rules all seem to be
syntactically correct.  I don't understand...  Any help, in certain or guess
form, is appreciated.

Kim


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