>> +  (match:substring (regexp-exec (profile-rx profile)
>> +                                (basename (readlink profile))) 1))

> Instead write:

>   (and=> (regexp-exec ...)
>          (cut match:substring <> 1))

> So that the thing returns #f when there are is no associated profile
> number.  OTOH, does that ever occur?

I doubt so, but I also think that it would be better to keep 'and=>' to
prevent possible problems.

> It should be based on rename(2) to be atomic.  See the ‘switchLink’
> function in Nix for how to do it.

Could you elaborate? Should I call C from Guile?

Nikita