[tex-hyphen] Hyphenation of Uyghur

[Jonathan Kew]

On 26/02/2021 22:00, Yannis Haralambous wrote:
> dear TeX-hyphen members,
> 
> I'm new to this list (although not necessarily new to TeX hyphenation :-)
> 
> Here is the problem: we are preparing hyphenation patterns for Uyghur, 
> written in Arabic script.
> As letters must be in initial/medial form before the hyphen and 
> medial/final form on the next line begin,
> I was wondering if we could change TeX internals so that instead of one, 
> three hyphenchars are used:
> ^^^^200d and `-' on the upper line and ^^^^200d on the lower line, in 
> order to obtain the equivalent
> of \discretionary{^^^^200d-}{^^^^200d}{}

The problem with this is that it wouldn't be the appropriate 
\discretionary in the case where the letter before the hyphenation 
position is a right- (rather than dual-) joining character.

So it's not sufficient to just have an extended form of \hyphenchar; we 
would also need hyphenation patterns to record two different types of 
break position: one for a break between joined letters, and one for a 
break between non-joined letters.

Or else the engine needs to know (perhaps from the Unicode properties of 
the adjacent characters) which form to use -- but if we accept that the 
engine can use knowledge of specific Unicode properties here, then it 
can take responsibility for inserting the ZWJs internally, without 
needing to change \hyphenchar.

(On re-reading, perhaps that's more like what you meant anyway?)

JK

> 
> Arthur said he would have a different solution.
> 
> I would personally play with the DVI (resp. XDV) file, even though the 
> widths of initial/medial forms
> are quite different from those of final/isolated forms, which would 
> require a global redistribution of
> space in the line.
> 
> Cheers,
> 
> Yannis