DOSL7::profile return string "DOSL7::profile"

I have a problem with DOSL7::profile variable.

I have an small iRule:

when HTTP_REQUEST {

    set profile_name DOSL7::profile
}

when IN_DOSL7_ATTACK {
    log local0. "profile $profile_name, $DOSL7_ATTACKER"
}

$profile_name return "DOSL7::profile" string instead of DoS profile name assigned to VIP.

Question is: why? what's wrong with my small piece of code?