(define (monte-carlo trials experiment)
  (define (iter trials-remaining trials-passed)
    (cond ((= trials-remaining 0)
           (/ trials-passed trials))
          ((experiment)
           (iter (- trials-remaining 1) (+ trials-passed 1.0)))
          (else
           (iter (- trials-remaining 1) trials-passed))))
  (iter trials 0.0))

(define (random-in-range low high)
  (let ((range (- high low)))
    (+ low (random range))))

(define (estimate-integral p x1 x2 y1 y2 trials)
  (define rectangle-area (* (- x2 x1) (- y2 y1)))
  (define (experiment)
    (let ((x (random-in-range x1 x2))
          (y (random-in-range y1 y2)))
      (p x y)))
  (* (monte-carlo trials experiment)
     rectangle-area))

(define (estimate-pi trials)
  (estimate-integral (lambda (x y) (< (+ (* x x) (* y y)) 1))
                     -1.0 1.0
                     -1.0 1.0
                     trials))

; 1 ]=> (map estimate-pi (iota 10 1 1000))
; 
; ;Value: (4. 3.1888111888111887 3.1284357821089457 3.14161946017994 3.1342164458885278 3.1401719656068785 3.1421429761706383 3.1418368804456507 3.1466066741657293 3.15120542161982)