Hi,

I'm attaching a slightly modified version.

> Yeah, that’s expected.  Basically, if you do

>   guix-package -p /dev/null --roll-back

> it should fail with an error message saying that there is no previous
> profile or something like that.

'profile-number' will fail if I call it with a bogus file name.

For instance:

scheme@(guile-user)> (profile-number "/foo/bar")
ERROR: In procedure readlink:
ERROR: In procedure readlink: No such file or directory

What should I use to handle this error?  Please show an example.  The
ones from the manual aren't helpful.

I don't understand how to add a command-line option that should accept
an optional argument.  I commented out my attempts.

Nikita