[luatex] \predisplaydirection from etex in luatex has no effect

Taco Hoekwater taco at elvenkind.com
Thu Apr 8 12:10:50 CEST 2010

Vafa Khalighi wrote:
>     >From your description, wouldn't it make more sense if there is a
>     separate switch setting whether placing of \eqno and \leqno is
>     interchanged? That is, one that does not follow \mathdir but is
>     independent of it? A polyglossia- or babel-like package could then set
>     this correctly for the language in question.
> Yes but consider two things
> 1- the spacing of \eqno and \leqno are different. You can usually save
> some vertical space with \eqno but you can not with \leqno
> 2- We need to have some kind of primitive that actually interchanges
> \eqno and \leqno (I think) and the rest can be done in bidi.

It follows (if I understand everything correctly) that luatex itself
should *not* initialize \predisplaydirection based on the current
directions, but just set it to zero. Then, when it comes time to place
an equation number, it should base itself on \mathdir, but swap the
left&right if \pdfdisplaydirection=-1 (as set by the user).

Best wishes,

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