Philippe,

Philippe Veber wrote:
> I'm getting started with guix, and so far it's been just fine.

Welcome!

> I would like to see all available versions for a given package.
> Is there a command that would help me with that?

There is:

  $ guix package --list-available=^glibc$
  glibc	2.25	out,debug,static 
  gnu/packages/base.scm:921:2
  glibc	2.22	out,debug,static 
  gnu/packages/base.scm:980:2
  …

For easier interactive use, you can use the short option ‘-A’.

Note that this option takes a regular expression as argument. 
That makes it powerful, but means you'll have to enclose the name 
in ‘^…$’ if you want to match one specific package.

Kind regards,

T G-R