no base_path function

I tested this against Drupal 4.7 beta 4 ( ) and got this error:

Fatal error: Call to undefined function base_path() in /var/www/drupal/modules/sifr/sifr.module on line 614

...when I tried to add a rule, @

admin/settings/sifr/addrule

php --version
PHP 5.0.5-1.dotdeb.1 (cli) (built: Sep 7 2005 10:07:31)
Copyright (c) 1997-2004 The PHP Group
Zend Engine v2.0.5, Copyright (c) 1998-2004 Zend Technologies