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From "Steven Rowe (JIRA)" <>
Subject [jira] Commented: (LUCENE-1126) Simplify StandardTokenizer JFlex grammar
Date Fri, 11 Jan 2008 13:49:34 GMT


Steven Rowe commented on LUCENE-1126:

In part my imprecise characterization of the process comes from what is likely a misunderstanding
of the Lucene-Java release process - when you said:

bq. I'm not positive, but couldn't this result in situations where a committer using a 1.5
JVM could generate and commit a that had would have a different
behavior then if he was using 1.4 - all of which would be completely independent of whether
or not the release engineer of the next release compiled the resulting grammer using 1.4?

I assumed you meant that during the release process, the lexical scanner source (.java file)
would be regenerated from the grammar (.jflex file).  And in this scenario, I meant to refer
to "compile-time" as the entire build process - raw source to jar assembly, *including* lexical
scanner generation - undertaken when producing a binary release.

But of course you're right :) .  The JVM version being used during source-generation-time
(occurring prior to, and potentially not contiguously with, bytecode-generation-time) determines
the version of Unicode used to define the meaning of "letter" and "digit".

> Simplify StandardTokenizer JFlex grammar
> ----------------------------------------
>                 Key: LUCENE-1126
>                 URL:
>             Project: Lucene - Java
>          Issue Type: Improvement
>          Components: Analysis
>    Affects Versions: 2.2
>            Reporter: Steven Rowe
>            Priority: Minor
>             Fix For: 2.4
>         Attachments: LUCENE-1126.patch
> Summary of thread entitled "Fullwidth alphanumeric characters, plus a question on Korean
ranges" begun by Daniel Noll on java-user, and carried over to java-dev:
> On 01/07/2008 at 5:06 PM, Daniel Noll wrote:
> > I wish the tokeniser could just use Character.isLetter and
> > Character.isDigit instead of having to know all the ranges itself, since
> > the JRE already has all this information.  Character.isLetter does
> > return true for CJK characters though, so the ranges would still come in
> > handy for determining what kind of letter they are.  I don't support
> > JFlex has a way to do this...
> The DIGIT macro could be replaced by JFlex's predefined character class [:digit:], which
has the same semantics as java.lang.Character.isDigit().
> Although JFlex's predefined character class [:letter:] (same semantics as java.lang.Character.isLetter())
includes CJK characters, there is a way to handle this using JFlex's regex negation syntax
{{!}}.  From [the JFlex documentation|]:
> bq. [T]he expression that matches everything of {{a}} not matched by {{b}} is !(!{{a}}|{{b}})

> So to exclude CJ characters from the LETTER macro:
> {code}
>     LETTER = ! ( ! [:letter:] | {CJ} )
> {code}
> Since [:letter:] includes all of the Korean ranges, there's no reason (AFAICT) to treat
them separately; unlike Chinese and Japanese characters, which are individually tokenized,
the Korean characters should participate in the same token boundary rules as all of the other
> I looked at some of the differences between Unicode 3.0.0, which Java 1.4.2 supports,
and Unicode 5.0, the latest version, and there are lots of new and modified letter and digit
ranges.  This stuff gets tweaked all the time, and I don't think Lucene should be in the business
of trying to track it, or take a position on which Unicode version users' data should conform
> Switching to using JFlex's [:letter:] and [:digit:] predefined character classes ties
(most of) these decisions to the user's choice of JVM version, and this seems much more reasonable
to me than the current status quo.
> I will attach a patch shortly.

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