anchor.diff:  
   let
     inherit (lib) mkIf mkOption singleton types;
  -  inherit (pkgs) coreutils exim;
  +  inherit (pkgs) coreutils;
     cfg = config.services.exim;
   in
   
  
positive.code:         spool_directory = ${cfg.spoolDir}
          ${cfg.config}
        '';
        systemPackages = [ exim ];
      };
  
      users.users = singleton {
  
negative.code:         '';
        };
  
        package = mkOption {
          type = types.package;
          default = pkgs.exim;
          defaultText = "pkgs.exim";
          description = ''
            The Exim derivation to use.
            This can be used to enable features such as LDAP or PAM support.
          '';
        };
  
      };
  
    };
  