> Rather, I would do:

>   --delete-generations=3..9

> It’s easier to parse and to type.

> Likewise, it could even support:

>   --delete-generations=1month

Here’s what I decided to use:

--list-generations
--list-generations=10
--list-generations=1,32,9
--list-generations=4..10
--list-generations=11..
--list-generations=..13
--list-generations=first-month
--list-generations=last-month

I guess I have to write a parser for the “1,32,9” case, right?  Or is
there a simpler solution?

> Perhaps there could be several formats.  For instance,
> --list-generations would be equivalent to --list-generations=short:

>   generation 1     Dec. 16 2013
>   generation 2     May 7 2013

> And then --list-generations=long would do something like:

>   generation 1	   Dec. 16 2013
>     guile    2.0.7 out,debug    gnu/packages/guile.scm
>     hello    2.8   out          gnu/packages/base.scm

>   generation 2     May 7 2013
>     guile    2.0.9 out          gnu/packages/guile.scm

> WDYT?

OK, but how can I integrate this in the above scheme?  Will it be OK to
create an additional ‘--short’ switch or a new
‘--list-generations-short’ option?  Both solutions look ugly.

> I’ll have to disagree.  :-)

> There’s no such verb as “rollback”, I think, whereas “fallback” is a
> valid noun (and we don’t have the choice for “fallback”, since there are
> messages in the daemon that mention it.)

> Now, if you had --rollback as an alias, I won’t scream either...

See [1–4].  Would you like to keep ‘--roll-back’ anyway?

[1] https://en.wiktionary.org/wiki/rollback
[2] http://www.merriam-webster.com/dictionary/rollback
[3] http://www.thefreedictionary.com/rollback
[4] http://oxforddictionaries.com/us/definition/american_english/rollback