what does -> do in clojure, when I want to update keys in a map and pass that down? Does it re-bind?

try-a-threading-in-clojure

(def file-config-map {"channel-queue-size" "128", 
  "send-dir" "/tmp/foo/send", 
  "spool-dir" "/tmp/foo", 
  "file-rotation-period-ms" "1000", 
  "temp-dir" "/tmp/foo/temp", 
  "channel-timeout" "250", 
  "lineproto-port" "2003", 
  "target-list" "host-a,host-b,host-c,host-d"})

(defn parse-int [maybe-a-string]
  (println "Trying the number " maybe-a-string)
  (cond
   (number? maybe-a-string) maybe-a-string
   (nil? maybe-a-string) 0
   :else (Integer/parseInt maybe-a-string)))

(defn fix-config-types
  "All config types are read from disk as strings.  When they're
used, we need them to be other things - so far numbers and lists.
Convert those keys we know need to be convered here.  Note that this
currently doesn't allow for e.g. nested keys to be modified"
  [config]
  (-> config
      (into (for [k [config-numbers]] [k (parse-int (config k))]))
      (into (for [k [config-lists]] [k (clojure.string/split (config k) #"\s*,\s*")]))))