1. [root@nixos:/home/neo]# nix-env -f "<nixpkgs>" -qaP -A haskellPackages Cabal
  2. haskellPackages.Cabal_1_18_1_7 Cabal-1.18.1.7
  3. haskellPackages.Cabal_1_20_0_4 Cabal-1.20.0.4
  4. haskellPackages.Cabal_1_24_2_0 Cabal-1.24.2.0
  5. haskellPackages.Cabal_2_0_0_2 Cabal-2.0.0.2