[Nix-dev] undefined variable 'config', in '/etc/nixos/configuration.nix'

[Bryan Murdock]

I'm using nixos-0.1pre22440-i686-linux.iso to install nix as a
VirtualBox guest.  At the step where I run nixos-install it exits
early with this output:

building the system configuration...
error: undefined variable 'config', in '/etc/nixos/configuration.nix'

The file /etc/nixos/configuration.nix is this:

{config, pkgs, ...}:

{
  require = [./nixos/modules/installer/cd-dvd/installation-cd-graphical.nix];

  # Add your own options below nad run "nixos-rebuild switch".
  # E.G.,
  #    services.openssh.enable = true;
}

Bryan