SICP_3.5-3.6

(#%require (only racket/base random))

;;;;;;;;;3.5
(define (estimate-integral expriment x1 x2 y1 y2 trials)
  (let ((length (abs (- x2 x1)))
        (high (abs (- y2 y1))))
    (* (* high length) (monte-carlo trials expriment))))

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

;(define p1
;  (let ((x (random-in-range -1 1))
;        (y (random-in-range -1 1)))
;    (<= (+ (square x) (square y)) 1)))
(#%require (only racket/base random))

;;;;;;;;;3.5
(define (estimate-integral expriment x1 x2 y1 y2 trials)
  (let ((length (abs (- x2 x1)))
        (high (abs (- y2 y1))))
    (* (* high length) (monte-carlo trials expriment))))

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

;(define p1
;  (let ((x (random-in-range -1 1))
;        (y (random-in-range -1 1)))
;    (<= (+ (square x) (square y)) 1)))

(define p
  (lambda ()
    (let ((x (random-in-range 0 2))
          (y (random-in-range 0 2)))
      (>= 1 (+ (square (- x 1)) (square (- y 1)))))))

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

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

(exact->inexact (estimate-integral p 0 2 0 2 1000))

;;;;;;;;3.6
(define rand-init 1)

(define rand-update
  (lambda (x)
    (+ x 1)))

(define rand
  (let ((x rand-init))
    
    (define reset
      (lambda (value)
        (set!  x value)))

    (define generate
        (begin(set! x (rand-update x))
        x))

    (define (dispatch x)
      (cond ((eq? x 'generate) generate)
            ((eq? x 'reset) reset)
            (else (error "No such method -- rand" a))))
    dispatch))

(define rand1 
   (let ((x rand-init)) 
     (define (dispatch message) 
       (cond ((eq? message 'generate) 
               (begin (set! x (rand-update x)) 
                      x)) 
             ((eq? message 'reset) 
               (lambda (new-value) (set! x new-value))))) 
     dispatch))

(define rand2
  (let ((x rand-init))
    (define (generate)
      (set! x (rand-update x))
      x)
    (define (reset n)
      (set! x n))
    (define (dispatch a)
      (cond ((eq? 'generate a) (generate))
            ((eq? 'reset a) reset)
            (else (error "No such method -- rand" a))))
    dispatch))



;(rand 'generate)
;(rand 'generate)
;(rand 'generate)
;((rand 'reset) 3)
;(rand 'generate)

(rand2 'generate)
(rand2 'generate)
(rand2 'generate)
((rand2 'reset) 3)
(rand2 'generate)

1.被注释掉的p 不是一个过程，而是一个值 如果把rand-in-range 放后面会报错

2.也是同样的情况被注释掉的rand过程中 我试图直接把generate做成一个值，但是总是得不到正确的结果，

我想可能是因为，当generate 为数值时，它的数值的取决于rand中的x，而在这里就会 出现 x一直为

rand-init。如果把generate 做成一个无参过程，除了开始之外就不会依赖于rand 中的x了，从而每次都会update

自己的x了，可能和作用域有关