Re: [emacs-bidi] reordering based on implicit levels

[Eli Zaretskii]

On Mon, 12 Nov 2001, Alex Schroeder wrote:

> >> (when bidi-testing
> >>   (assert (string=
> >>       (bidi-reorder-string
> >>        "FOO is a word for FOOLS."
> >>        (bidi-resolve-implicit-levels
> >>         (bidi-resolve-weak-types
> >>          (bidi-get-types "FOO is a word for FOOLS."))))
> >>       "OOF is a word for SLOOF."))
> > 
> > Is this a left-to-right paragraph or a right-to-left one?  The result
> > is correct for the former.
> 
> This should be left to right.

Okay.  You should be aware, though, that by default, a logical
paragraph which begins with a strong R2L character will be displayed
as right-to-left (that's clause P1 in UAX#9).

> If you have a right to left paragraph,
> you need to pass an additional parameter to bidi-resolve-weak-types.
> 
>  (bidi-reorder-string
>   "FOO is a word for FOOLS."
>   (bidi-resolve-implicit-levels
>    (bidi-resolve-weak-types
>     (bidi-get-types "FOO is a word for FOOLS.")
>     t)))
> 
>  => " OOFis a word for.SLOOF "
> 
> This is obviously wrong.

I think you should invert the entire string first, if the paragraph is
right-to-left.  _Then_ apply your code to the inverted string.

The correct result for the above example is this:

  .SLOOF is a word for OOF

(I didn't actually test this, so the period could be a problem.)

> Yes, I think my main problem is that I implemented logical to visual
> conversion without explicit levels, and I'm not sure what needs to be
> changed exactly in order to make that a visual to logical conversion.
> :)

I think, except for the inversion I mentioned, you shouldn't need
anything.