TCL error for basic ACL iRule

Can simplify it a bit:

when RULE_INIT {
     v1.0 - basic ACL.
     January, 2014
    
     Purpose: 
       Bind this rule to a virtual server to simply allow or disallow traffic based on source IP. 
       This rule expects a datagroup that lists the addresses you wish to allow. 
       By default, traffic will be dropped.
    }
    when CLIENT_ACCEPTED  {
            if { ! [class match [IP::client_addr] equals allowed_datagroup] }{
                    log local0. "Invalid client IP: [IP::client_addr] - discarding"
                    discard
            }
    }