SICP exercise 1.35

sicp_exercise_1_35.scm

(define (expect actual expectation expected)
  (display "• ")
  (display actual)
  (display " should equal ")
  (display expected)
  (display ": ")
  (expectation actual expected)
  (display "pass\n")
  )
  
(define (to-equal actual expected)
  (assert (= actual expected)))
  
(define (to-be-close actual expected)
  (assert (< (abs (- actual expected)) 0.0001)))

(define (to-be actual expected)
  (if expected
    (assert actual)
    (assert (not actual))))

(define tolerance 0.00001)

(define (fixed-point f first-guess)
  (define (close-enough? v1 v2)
    (< (abs (- v1 v2)) tolerance))
  (define (try guess)
    (let ((next (f guess)))
      (if (close-enough? guess next)
        next
        (try next))))
  (try first-guess))
  
(expect (fixed-point cos 1.0) to-be-close 0.7391)

(expect (fixed-point (lambda (x) (+ 1 (/ 1 x))) 1.0) to-be-close 1.61803399)