anchor.diff:  
     config = mkIf cfg.enable {
   
  -    environment.systemPackages = [ cfg.package ];
  +    environment.systemPackages = [ postgresql ];
   
       launchd.user.agents.postgresql =
  -      { path = [ cfg.package ];
  +      { path = [ postgresql ];
           script = ''
             # Initialise the database.
             if ! test -e ${cfg.dataDir}/PG_VERSION; then
  
positive.code: 
  let
    cfg = config.services.postgresql;
  
    configFile = pkgs.writeText "postgresql.conf"
      ''
  
negative.code:         '';
        };
  
        extraPlugins = mkOption {
          type = types.listOf types.path;
          default = [];
          example = literalExample "[ (pkgs.postgis.override { postgresql = pkgs.postgresql94; }) ]";
          description = ''
            When this list contains elements a new store path is created.
            PostgreSQL and the elements are symlinked into it. Then pg_config,
            postgres and pg_ctl are copied to make them use the new
            $out/lib directory as pkglibdir. This makes it possible to use postgis
            without patching the .sql files which reference $libdir/postgis-1.5.
          '';
        };
  
        extraConfig = mkOption {
          type = types.lines;
          default = "";
  