1: { }: 2: with builtins; 3: with { 4: nixpkgs = with tryEval <nixpkgs>; 5: if success then value else abort "Don't have <nixpkgs>?!"; 6: }; 7: 8: new: env: 9: env // { 10: NIX_PATH = "nixpkgs=${toString new}:real=${toString nixpkgs}"; 11: }