[luatex] Simple bidi

[Javier Bezos]

I was intrigued by the possibility to devise a simple bidi algorithm
based on some assumptions -- Arabic by default, flat text (ie, no
nested directions), no math, etc. Since TeX is a markup language, I've
just ignored LRE, PDF end the like. One of my aims was to set
directions with just one loop, instead a series of them.

I managed to do it, with a second smaller loop for a special
case. Attached is the resulting code, which works in typical cases. I
tried to emulate the unicode behavior, but I'm not sure it's fully
compliant (I'd say it's not, but who knows :-)).  I have to add a few
things (eg, NSM, but little more, I hope).

Please, let me know if you find cases where the result is not what you
would expect, to improve it. The text has been copy-pasted from
Wikipedia (the only changes are % -> \%, and an extra [; I think
%68.3- has been wrongly entered).

(The bidi database is that by Khaled Hosny.)

Javier

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