How to get Symbol in cmd+R to display for a new language?


I’ve recently added a new language support in atom (my company’s own programming language, with extension .fgl).
And unfortunately i cannot use cmd+R to display the function list.
It worked pretty well for other file extentions, e.g. .sql, .asp, and once I change my language file to a known extension I can see the function list using cmd+R.

I’ve tried ctag-gen and some other packages and still can’t get my function displayed.

Can anyone give me some hints please?