[antlr-interest] NoViableAltException in tree grammar

[Tom Smith]

On Thu, Jul 10, 2008 at 11:41 AM, Jim Idle <jimi at temporal-wave.com> wrote:

> ... Then, while ANTLR will generally work things out for you, you should
> really factor all your parser rules for common sequences, then rewrite the
> token stream with different root nodes if you need to distinguish between
> combinations. This will generally give you the most streamlined parser and
> an AST with no ambiguities (which is what you want). So:
>
>
> top
>     : BEFORE AFTER?
>     | AFTER
>     ;
>

After going back to my original (larger) grammar (complete with lexer
rules!) and factoring out the common part as Jim suggested, the
NoViableAltException went away. I don't yet understand why, but until my
understanding matures, I'll check for left-factoring opportunities when I
run into problems!

Thanks,
Tom.
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