That's bad.  It seems, I forgot to add the fallbacks properly.  I will reach out to the designer to add those chars.

On Fri, Mar 12, 2021 at 12:32 PM Hans Hagen <j.hagen@xs4all.nl> wrote:

On 3/11/2021 2:05 AM, Mohammad Hossein Bateni wrote:
> Hi,
>
> Since most fonts do not have the standard tex ligatures built in, I tend
> to add them when I load the fonts.  Once in a while, I run into fonts
> where this does not work.
>
> See the attached tex/pdf files.  I basically load the font as follows:
>
> \definefontfeature[tf][arabic][tlig=yes]
> \definedfont[dejavusansmono*tf]
>
> This works fine for DejaVuSansMono and for one Farsi font I use
> (https://github.com/rastikerdar/vazir-font/blob/master/dist/Vazir-Regular.ttf
> <https://github.com/rastikerdar/vazir-font/blob/master/dist/Vazir-Regular.ttf>)
> but not for this other Farsi font
> (https://github.com/aminabedi68/Mikhak/blob/master/Font/ttf/Mikhak-Medium.ttf
> <https://github.com/aminabedi68/Mikhak/blob/master/Font/ttf/Mikhak-Medium.ttf>). 
> Perhaps this is because the last font is not standard, but
> TrueType/OpenType standard is sometimes up for interpretation.
>
> I see two strange symptoms here:
>
> \showotfcomposition displays the tlig feature differently for the last
> font.  It appears in the "extra" list, not in "basic".  Why is that? 
> What does this mean anyway?

The font doesn't have endash and emdash so there is nothing to construct
from the double -

\starttext
     \definedfont[file:Mikhak-Medium.ttf*default] foo--bar
     [\char"2013]
     [\char"2014]
\stoptext

Just ask the author to add these characters and you're fine.

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------