(defn r-squared [x y]
 (+ (* (- 0.5 x) (- 0.5 x))
    (* (- 0.5 y) (- 0.5 y))))


(defn calculate-pi [throws]
	(loop [hits 0
         throws-left throws] ; initial number of throws
      (zero? throws-left) (* 4.0 (/ hits throws)); all thrown, return value
      (<= (r-squared (rand) (rand)) 0.25) (recur (inc hits) (dec throws-left))
	  (> (r-squared (rand) (rand)) 0.25) (recur hits (dec throws-left))
	)
)

java.lang.UnsupportedOperationException: Can only recur from tail position (Assi
gnment1.clj:20)