SICP Chapter 3.1

sicp_chapt3.1.scm

;; 3.1
(define (make-accumulator sum)
  (lambda (n) (set! sum (+ sum n))))

;; 3.2
(define (make-monitored f)
  (let ((count 0))
    (lambda (param)
      (cond ((eq? 'how-many-calls? param) count)
            ((eq? 'reset param) (set! count 0))
            (else (set! count (+ 1 count))
              (f param))))))

;; 3.3
(define (make-account balance passwd)
  (define (withdraw amount)
    (if (>= balance amount)
      (begin (set! balance (- balance amount)))
      "Insufficient founds"))
  (define (deposit amount)
    (set! balance (+ balance amount)))
  
  (lambda (pass m)
    (if (eq? pass passwd)
      (cond ((eq? m 'withdraw) withdraw)
            ((eq? m 'deposit) deposit))
      "Incorrect Password")))

;; 3,4		
(define (call-the-cops) (print "Cop! Here!!"))

(define (make-account2 balance passwd)
  (define (withdraw amount)
    (if (>= balance amount)
      (begin (set! balance (- balance amount)))
      "Insufficient founds"))
  (define (deposit amount)
    (set! balance (+ balance amount)))
  
  (let ((count 0))
    (lambda (pass m)
	  (if (eq? pass passwd)
        (cond ((eq? m 'withdraw) (set! count 0) withdraw)
              ((eq? m 'deposit)  (set! count 0) deposit))
        (begin (set! count (+ count 1)) 
               (if (= count 7) (lambda (m) (call-the-cops))
                   (lambda (m) "Incorrect password")))))))

;; 3.5
(use data.random)
(use gauche.generator)

(define (random-in-range lo hi)
  (+ (* (car (generator->list (reals-between$ 0 1) 1)) (- hi lo)) lo))


(define is-in-circle
  (lambda ()
    (<= (+ (square (- (random-in-range 2 8) 5)) 
           (square (- (random-in-range 4 10) 7)))
      (square 3))))
      

(define (monte-carlo trial expr)
  (define (iter n success)
    (cond ((>= n trial) (/ success trial))
          ((expr) (iter (+ n 1) (+ success 1)))
          (else (iter (+ n 1) success))))
  (iter 0 0))


;; 3.6
(define rand
  (let ((x 4112))
    (lambda (cmd)
      (cond ((eq? 'reset cmd) (lambda (new-val) (set! x new-val)))
            ((eq? 'generate cmd) (set! x (mod (+ (* 134214 x) 421441) 1000))
                                 (inexact (/ x 1000)))
            (else (error "Invarid Command"))))))

;;3.7

;;3.8
(define f
  (let ((b4 9999))
    (lambda (p)
      (cond ((= b4 9999) (begin (set! b4 p) 0))
            ((= b4 0) 0)
            (else 1)))))