[Nix-dev] two versions of emacs installed

[Bryan Murdock]

The most intriguing feature of nixos for me is being able to have
multiple versions of the same software installed.  I just got nixos
running as a virtualbox guest and that's the first thing I tried and
it didn't work.  I installed emacs 23:

nix-env -i emacs-23.2

and that worked just fine.  Then I tried to install emacs 22:

nix-env --preserve-installed -i emacs-22.3

But I got errors:

Collission between
'/nix/store/sdfx8jya9ijci7d7xm70fk7wv8zw5z3v-emacs-22.3/bin/b2m' and
'/nix/store/nhkyz3ls880i21319wmr17qyrgzzmn98-emacs-23.2/bin/b2m'.
Suggested solution: use 'nix-env --set-flag priority NUMBER PKGNAME'
to change the priority of one of the conflicting packages.
builder for '/nix/store/wj8jgvrjaf6ki5qs2kcg3kfbhnccjppr-user-environment.drv'
failed with exit code 255
error: build of
'/nix/store/wj8jgvrjaf6ki5qs2kcg3kfbhnccjppr-user-environment.drv'
failed

I honestly would be fine without b2m, but I'm confused as to what is
going on and how to resolve it.

Bryan