[tex-hyphen] versioning hyphenation patterns

[Stephan Hennig]

Werner LEMBERG schrieb:
>> > Mojca, have you ever thought about pattern versions?  One of the
>> > very first emails to the tex-hyphen mailing list discusses that.
>> > Since luatex will support selection of patterns as a run-time
>> > operation (at least this is what I remember), this might become an
>> > issue.
>>
>> At the very beginnig Karl said something like:
>> - please no pattern version in the name
> 
> Hmm.  In german-x, we'll have the following:
> 
>   dehypht-x.tex
>   dehypht-x-2008-06-15.tex
> 
> The former loads the latter, thus for the end user it's always
> `dehypht-x.tex'.  All those files are generated automatically by the
> project's Makefile.
> 
>> Do you have any suggestion about how to use the versioned files?
> 
> No.  First, we need a TeX system which supports hyphenation pattern
> selection at run-time.

This is not entirely true.  Heiko Oberdiek has recently contributed
package hyphsubst that can replace the patterns bound to a language
identifier.  This works for all patterns that are loaded in a format.
As an example, the code

\RequirePackage{hyphsubst}
\documentclass{article}
\HyphSubstLet{ngerman}{english}
\usepackage[ngerman]{babel}
\begin{document}
\showhyphens{Hyphenation}
\end{document}

actually uses English patterns, despite the fact that German language is
active (as far a Babel is concerned).

That is, using versioned patterns we need unique identifiers for all
patterns (for 8-bit TeX).  We're currently simply appending the package
date to language and pattern file names.  But for users, I think simple
version numbers are more easy to remember than ISO dates.

For 16-bit TeX I don't think all pattern version have to be built into
the format.  So a package (polyglossia?) could provide a key, say
version, for controlling loading of pattern files.  Using versioned
patterns shouldn't be the standard uses case.

Best regards,
Stephan Hennig

BTW, is LuaTeX able to merge different pattern files on the fly, e.g., a
language pattern file with a pattern file for domain specific notions?