(defn square [x] (* x x))

(defn good-enough? [previous current]
  (>=
    (* current 0.0001)
    (math/abs (- current previous))))

(defn improve [guess x]
  (/
    (+ (* 2 guess) (/ x (square guess)))
    3))

(defn cbrt-iter [prev guess x]
  (if (good-enough? prev guess)
          guess
          (cbrt-iter guess (improve guess x) x)))

(defn cube-root [x]
  (cbrt-iter 0.0 x x))

(var i 0.0000001)
(while (<= i 1000000000000.0)
  (def meas (cube-root i))
  (def rel (/ (- meas (math/cbrt i)) meas))
  (print (string/format "Relative error %f=%f, %f" (math/cbrt i) meas rel))
  (set i (* i 3.141519)))