anchor.diff:  
         enable = mkEnableOption "File Roller, an archive manager for GNOME";
   
  +      package = mkOption {
  +        type = types.package;
  +        default = pkgs.gnome.file-roller;
  +        defaultText = literalExpression "pkgs.gnome.file-roller";
  +        description = "File Roller derivation to use.";
  +      };
  +
       };
   
     };
  
positive.code: 
    ###### implementation
  
    config = mkIf config.programs.file-roller.enable {
  
      environment.systemPackages = [ pkgs.gnome.file-roller ];
  
      services.dbus.packages = [ pkgs.gnome.file-roller ];
  
    };
  
  
negative.code: 
  with lib;
  
  let cfg = config.programs.file-roller;
  
  in {
  
    # Added 2019-08-09
    imports = [
  