clojure.lang.LazySeq cannot be cast to clojure.lang.IFn

Question

I'm new to Riemann and Clojure. All I want to do is to send email notifications to three email groups when some service's TTL is expired. I created some sort of config file where I store a list of emails:

{
  :email_group_1 (
                  "[email protected]"
                  "[email protected]"
                 )
  :email_group_2 (
                  "[email protected]"
                 )
}

My riemann config looks like this:

(logging/init {:console true})
(import org.apache.log4j.Level)
(logging/set-level Level/DEBUG)

(require '[clojure.java.io :as io])
(import '[java.io PushbackReader])

(let [host "0.0.0.0"]
  (tcp-server {:host host :port 60001})
  (udp-server {:host host})
  (ws-server  {:host host :port 60003}))
(repl-server  {:host "127.0.0.1"})

(def cwd (System/getProperty "user.dir"))

(def emails
  (with-open [r (io/reader (str cwd "/etc/emails.clj"))]
             (read (PushbackReader. r))))

(periodically-expire 5)

(def email (mailer))

(defn notify [& egroups]
  (for [egroup egroups]
    (rollup 1 60 (apply email (emails egroup)))))

(let [index (index)]
  (streams
    (default :ttl 60
      index

      (expired
          (where (service "service_connect_active")
                    #(info "expired" %)
                    (notify :email_group_1 :email_group_2))))))

Code looks good (for me), but when this service is expired I get the following error:

09:45:39 riemann.1      | INFO [2015-05-08 10:45:39,313] Thread-5 - riemann.config - expired {:ttl 60, :time 357766884827/250, :state expired, :service service_connect_active, :host ava.local}
09:45:39 riemann.1      | WARN [2015-05-08 10:45:39,319] Thread-5 - riemann.config - clojure.lang.LazySeq@841649b8 threw
09:45:39 riemann.1      | java.lang.ClassCastException: clojure.lang.LazySeq cannot be cast to clojure.lang.IFn
09:45:39 riemann.1      |   at riemann.config$eval66$stream__70$fn__75.invoke(riemann.development.config:34)
09:45:39 riemann.1      |   at riemann.config$eval66$stream__70.invoke(riemann.development.config:45)
09:45:39 riemann.1      |   at riemann.streams$match$stream__3514$fn__3525.invoke(streams.clj:1209)
09:45:39 riemann.1      |   at riemann.streams$match$stream__3514.invoke(streams.clj:1209)
09:45:39 riemann.1      |   at riemann.streams$default$stream__3731$fn__3742.invoke(streams.clj:1328)
09:45:39 riemann.1      |   at riemann.streams$default$stream__3731.invoke(streams.clj:1328)
09:45:39 riemann.1      |   at riemann.core$stream_BANG_$fn__4415.invoke(core.clj:19)
09:45:39 riemann.1      |   at riemann.core$stream_BANG_.invoke(core.clj:18)
09:45:39 riemann.1      |   at riemann.core$reaper$worker__4529$fn__4539.invoke(core.clj:303)
09:45:39 riemann.1      |   at riemann.core$reaper$worker__4529.invoke(core.clj:297)
09:45:39 riemann.1      |   at riemann.service.ThreadService$thread_service_runner__1973$fn__1974.invoke(service.clj:71)
09:45:39 riemann.1      |   at riemann.service.ThreadService$thread_service_runner__1973.invoke(service.clj:70)
09:45:39 riemann.1      |   at clojure.lang.AFn.run(AFn.java:22)
09:45:39 riemann.1      |   at java.lang.Thread.run(Thread.java:745)

Could someone please help me? Thanks.

Answer 1

The "cannot to be cast to clojure.lang.IFn" error invariably points to something that is expecting a function being given something that cannot be treated as such...

(defn notify [& egroups]
  (for [egroup egroups]
    (rollup 1 60 (apply email (emails egroup)))))

This returns a for-generated LazySeq of rollup streams, not an actual stream (in Riemann a stream is-an IFn). So when Riemann tries to invoke the stream as an IFn your error occurs...

How about something like:

(defn notify [& egroups]
  (rollup 1 60 (apply email (mapcat emails egroups))))

Here we just convert the list of groups to a list of emails upfront and then get on with our lives.

Alternatively if you really want multiple streams (avoiding shared To: lines for example), then apply them to the rollup.

(defn notify [& egroups]
  (apply rollup 1 60 (map email (map emails groups))))

Hope this helps, I obviously don't have your whole config replicated.