otf ligature rendering support?

[Yuri D'Elia]

Hi everyone,

I'm not fully aware of how much otf is supported in emacs, but I found a
good reason to want ligatures in a monospaced font:

http://www.fsd.it/fonts/pragmatapro/PragmataPro_Haskell_liga.png

PragmataPro supports ligatures for a good set of common operators. This
makes it much less troublesome than "prettify-symbols-mode" since
indentation/spacing is not changed.

How would I enable the proper GSUB feature in emacs? Are ligatures
supported at all?

I can specify otf parameters in `font-spec', but the following:

(set-fontset-font nil 'latin
                  (font-spec :family "PragmataPro"
                             :otf '(latn nil (liga))))

Doesn't really show any ligatures (or any other otf feature).
Am I doing something wrong?