[antlr-interest] Possible bug in subrule invertion
Terence Parr
parrt at cs.usfca.edu
Fri Apr 9 10:26:20 PDT 2004
On Apr 9, 2004, at 10:09 AM, Mike Lischke wrote:
> Hi all,
>
> It seems like I found a bug in the subrule invertion parser. When I
> try to invert a set of tokens like:
>
> ~('*' | LINE_FEED)
>
> Where LINE_FEED is a (lexer) token defined as '\r'. ANTLR throws an
> error ("This subrule cannot be inverted....") however when I use
>
> ~('*' | '\r')
>
> The construct is accepted. So to me it looks like a bug. Is this a
> known problem?
If this is in the lexer, you cannot invert "rules" such as LINE_FEED.
Done on purpose, I'm afraid. ;)
> Btw.: It would be very helpful if we could do some "token set maths"
> like
>
> DIGIT: '0'..'9';
> OCTAL_DIGIT: DIGIT - ['8', '9'];
>
> In this simple example it would be easy to replace the octal digit
> rule however for large sets like Unicode it is necessary to
> selectively take out arbitrary ranges of code points as they are not
> defined yet.
Ah. Like a set intersection operator and such?
Ter
>
> Mike
> --
> www.soft-gems.net
>
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