Ex-1.46

(define (iterative-improve good-enough? improve-guess)
  (define (proc guess)
    (if (good-enough? guess) guess
        (proc (improve-guess guess))))
  proc)

;sqrt
(define (average x y)
  (/ (+ x y) 2.0))
(define (sqrt x)
  ((iterative-improve
    (lambda (guess)
      (< (abs (- (square guess) x)) 0.001))
    (lambda (guess)
      (average guess (/ x guess)))) x))

;fixed-point
(define tolerance 0.00001)
(define (fixed-point f first-guess)
  ((iterative-improve
    (lambda (guess)
      (< (abs (- guess (f guess))) tolerance))
    (lambda (guess) (f guess))) first-guess))