compute pi via monte carlo

pi.clj

(defn circle-test [x y]
   (not ( > ( + (* (- x 0.5) (- x 0.5)) (* (- y 0.5) (- y 0.5))) 0.25)))

  (defn error [est]
   (Math/abs (* (/ (- Math/PI est) Math/PI) 100)))

  (defn pi [n]
   (loop [hits 0 total 0]
    (let [x (rand) y (rand)]
     (if (< total n)
      (recur (if (circle-test x y) (inc hits) hits) (inc total))
      (* (/ hits total) 4.0)))))

  (defn estimate-pi [shots runs]
   (loop [r 0 vals ()]
    (let [est (pi shots)]
     (if (= r runs)
      (/ (reduce + vals) (count vals))
      (recur (inc r) (conj vals est))))))

  (defn print-estimate [est]
   (println est)
   (println (str (error est) "%")))