Detect if node is half-dead with an iRule?

[root@ve1023:Active] config  b rule myrule list
rule myrule {
   when RULE_INIT {
   set static::response_timeout  5
}

when HTTP_REQUEST {
   log local0. "Received request, beginning response monitor interval. [clock seconds]"
   set monitor_id [\
      after $static::response_timeout {
         HTTP::retry [HTTP::request]
         log local0. "Timeout $static::response_timeout milliseconds elapsed without server response. [clock seconds]"
      }\
   ]
}

when HTTP_RESPONSE {
   log local0. "Received server response."
   if {[info exists monitor_id]} {
      log local0. "Canceling after script with id $monitor_id"
      after cancel $monitor_id
   }
}
}

 curl -i http://172.28.19.79
curl: (52) Empty reply from server

[root@ve1023:Active] config  tail -f /var/log/ltm
Nov 18 09:58:15 local/tmm info tmm[24220]: Rule myrule : Received request, beginning response monitor interval. 1321639095
Nov 18 09:58:15 local/tmm err tmm[24220]: 01220001:3: TCL error: myrule  - Illegal argument. Can't execute in the current context. (line 1)     invoked from within "HTTP::request"

[root@ve1023:Active] config  tcpdump -nni 0.0 port 80 or port 88
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on 0.0, link-type EN10MB (Ethernet), capture size 108 bytes
09:58:15.745873 IP 172.28.19.253.57665 > 172.28.19.79.80: S 2312572844:2312572844(0) win 5840 
09:58:15.745910 IP 172.28.19.79.80 > 172.28.19.253.57665: S 1192813388:1192813388(0) ack 2312572845 win 4380 
09:58:15.748842 IP 172.28.19.253.57665 > 172.28.19.79.80: . ack 1 win 46 
09:58:15.748861 IP 172.28.19.253.57665 > 172.28.19.79.80: P 1:155(154) ack 1 win 46 
09:58:15.748956 IP 200.200.200.10.57665 > 200.200.200.101.88: S 498213601:498213601(0) win 4380 
09:58:15.749863 IP 200.200.200.101.88 > 200.200.200.10.57665: S 2493742844:2493742844(0) ack 498213602 win 5792 
09:58:15.749871 IP 200.200.200.10.57665 > 200.200.200.101.88: . ack 1 win 4380 
09:58:15.749885 IP 200.200.200.10.57665 > 200.200.200.101.88: P 1:155(154) ack 1 win 4380 
09:58:15.751050 IP 200.200.200.101.88 > 200.200.200.10.57665: . ack 155 win 54 
09:58:15.754080 IP 200.200.200.10.57665 > 200.200.200.101.88: R 155:155(0) ack 1 win 4380
09:58:15.754088 IP 172.28.19.79.80 > 172.28.19.253.57665: R 1:1(0) ack 155 win 4534