;testing for nothing
(defn null-v1? [lat]
  (or (empty? lat) (and (= (first lat) nil) (= (count lat) 1))))
(defn null-v2? [lat]
  (comp nil? lat))

;some sample lists
(def foods (list "owl curry" "rack of owl" "chicken-fried owl" "owl a la mode"))
(def reactions (list "delightful" "succulent" "paradoxical" "decadent"))

;a simple recursive function using a tail-recursive style
(defn eat [lat ladj null-pred?]
  (cond (null-pred? lat) "*burp*" (null-pred? ladj) "I'm afraid I must be leaving now. I'm barfing."
        :else (str "Mmm, " (first lat) ". How " (first ladj) ". " (eat (rest lat) (rest ladj) null-pred?))))

(time (eat foods reactions null-v1?))
;"Elapsed time: 0.08 msecs"
;=> "Mmm, owl curry. How delightful. Mmm, rack of owl. How succulent. Mmm, owl wellington. How extravagant. Mmm, chicken-fried owl. How velvety. Mmm, owl a la mode. How decadent. *burp*"
(time (eat foods reactions null-v2?))
;"Elapsed time: 0.043 msecs"
;=> "*burp*"