Is current_user a function ?

Hi,

As for some current_*** functions, "select current_user;" seems to
work, but "select current_user();" doesn't . Though current_user is
defined as one of functions, why does such an error occur ?

renew=# select current_user();
ERROR: parser: parse error at or near "(" at character 20

Regards,
Masaru Sugawara

renew=# \df
List of functions
Result data type | Schema | Name | Argument data types
---------------------+------------+-----------------------+-----------
...
name | pg_catalog | current_database |
name | pg_catalog | current_schema |
name[] | pg_catalog | current_schemas | boolean
text | pg_catalog | current_setting | text
name | pg_catalog | current_user |
...

renew=# select current_user();
ERROR: parser: parse error at or near "(" at character 20

renew=# select current_database();
current_database
------------------
renew
(1 row)

renew=# select current_schema();
current_schema
----------------
public
(1 row)

renew=# select current_schema(true);
current_schemas
---------------------
{pg_catalog,postgres,public}
(1 row)

renew=# select current_schema(false);
current_schemas
---------------------
{postgres,public}
(1 row)

renew=# select current_setting('search_path');
current_setting
-----------------
$user,public
(1 row)