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Steven Rowe commented on LUCENE-1126:
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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 StandardTokenizerImpl.java 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?
Yes, you're right - I was conceiving of the resulting lexer building the tables
at runtime, but looking at the code in StandardTokenizerImpl.java, that's
patently false - this, as you point out, is a compile-time operation.
And when I compile with 1.4.2, the resulting StandardTokenizerImpl.java file is
significantly different from the result with 1.5.0.
I'm quite sure, despite this, that switching to the (compile-time) JVM's
Unicode version's definitions of letters and digits is a better policy than
depending on a non-existent update mechanism for the grammar.
> Simplify StandardTokenizer JFlex grammar
> ----------------------------------------
>
> Key: LUCENE-1126
> URL: https://issues.apache.org/jira/browse/LUCENE-1126
> Project: Lucene - Java
> Issue Type: Improvement
> Components: Analysis
> Affects Versions: 2.2
> Reporter: Steven Rowe
> Priority: Minor
> Fix For: 2.4
>
>
> 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|http://jflex.de/manual.html]:
> 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 letters.
> 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 to.
> 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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