#lang sicp
(define (iterative-improve good-enough?
                           improve)
  (define (rec-procedure guess)
    (define new-guess (improve guess))
    (if (good-enough? guess new-guess)
        new-guess
        (rec-procedure new-guess)))
  rec-procedure)

(define (square x)
  (* x x))

(define (average a b)
  (/ (+ a b)
     2))

(define (sqrt x)
  (define tolerance 0.000001)
  (define (good-enough? guess)
    (< (abs (- (square guess) x)) tolerance))
  (define (improve guess)
    (average guess (/ x guess)))
  (iterative-improve good-enough? improve))