Re: [I18nrp] Mappings for IDNA2008 ?

[Martin J. Dürst <[e-mail]>]

Hello Patrick, others,

On 2019/02/09 04:16, Patrik Fältström wrote:
> On 8 Feb 2019, at 9:20, Martin J. Dürst wrote:

>> If we take the case of Turkish, then the generic mapping tables are useful because once we have them, a suitable Turkish mapping can be defined as a small delta (e.g. a small preprocessing step) to the generic mapping tables.

> As you need this extra local delta, JUST using the plain mapping is wrong, include errors, and can not be used.
> 
> You MUST use the generic mapping (as you name it) PLUS the specific exceptions.
> 
> And it is definitely not the case that you can do f(x) and then f'(x), i.e. f(f'(x)) but instead you need to use y(x) as the function where y(x) is as you write f(x) modified with the delta that the LOCALE defines.
> 
> If one could do f(f'(x)) then it would be easy.

If f(x) is the generic mapping, and f'(x) is the mapping of the 
exceptions, then f(f'(x)), which applies f' *before* f, should do the job.

Proof: If it doesn't, just change f' to include the cases that were not 
taken into account correctly. You may have to do this several times. In 
the end, you may end up with f' doing all the work, and f no longer 
having to do anything, but there should not be any such cases in 
practice (not the least because each locale will leave mappings for 
scripts and characters not used in that locale to the generic mapping).

As an example, if f' for Turkish is defined as follows:
f'(I) → ı
f'(İ) → i
f'(_x_) → _x_     # leave everything else alone

then things should work for Turkish.

Regards,   Martin.