I want use date() in Plugin

[SANBOR]

hi
I Want Replases function date() With jdate()
but i insert new plugin and i give error

Fatal error: Cannot redeclare date() in D:\xampp\htdocs\vbulletin\global.php(29) : eval()'d code on line 6

my new plugin is :
hook = global_start

function date($format, $timestamp = TIMENOW, $doyestoday = false, $locale = true, $adjust = true, $gmdate = false, $userinfo = '')
{
require_once(DIR . '/includes/jalali.php');
global $vbulletin, $calendarinfo, $vbphrase, $serveroffset, $blog, $start, $forum, $thread;
return jdate($format ,$timestamp=' ',$none='' ,$time_zone=''  ,$tr_num='fa');
}

how do ?