[Nix-dev] newbie question: Which name is used for eclipse-sdk-4.4 in /etc/nixos/configuration.nix

[Niklaus Giger]

Hi everybody

Thanks to lwn pointing me to NixOS I decided to test drive using VirtualBox. I 
was quite impressed how much was available and how smooth my experience has 
been.

I am puzzleed that runnig
nix-env -i eclipse-sdk-4.4
works fine, but I was unable to add it /etc/nixos/configuration.nix with lines 
like
{
  environment.systemPackages =
    [ pkgs.eclipse-sdk-4.4
	]
}
failed. 

Similarly I was surprised that nix-env -i kdepim needed a item called 
pkgs.kde4.kdepim in /etc/nixos/configuration.nix.

Could anybody point give me an explanation or point me to where I find one for 
this behaviour? I did not find one under https://nixos.org/wiki/FAQ, 
http://nixos.org/nix/manual/ nor http://nixos.org/nixpkgs/manual/.

Best regards

Niklaus