sicp: section 3.1

sicp/3/1/1.scm

+(define balance 100)
+
+(define (withdraw amount)
+  (if (>= balance amount)
+    (begin (set! balance (- balance amount))
+           balance)
+    "Insufficient funds"))
+
+(display (withdraw 25))
+(newline)
+(display (withdraw 25))
+(newline)
+(display (withdraw 60))
+(newline)
+(display (withdraw 15))
+(newline)
+
+(define new-withdraw
+  (let ((balance 100))
+    (lambda (amount)
+      (if (>= balance amount)
+        (begin (set! balance (- balance amount))
+               balance)
+        "Insufficient funds"))))
+
+(newline)
+(display (new-withdraw 25))
+(newline)
+(display (new-withdraw 25))
+(newline)
+(display (new-withdraw 60))
+(newline)
+(display (new-withdraw 15))
+(newline)
+
+(define (make-withdraw balance)
+  (lambda (amount)
+    (if (>= balance amount)
+      (begin (set! balance (- balance amount))
+             balance)
+      "Insufficient funds")))
+
+(define W1 (make-withdraw 100))
+(define W2 (make-withdraw 100))
+(newline)
+(display (W1 50))
+(newline)
+(display (W2 70))
+(newline)
+(display (W2 40))
+(newline)
+(display (W1 40))
+(newline)
+
+(define (make-account balance)
+  (define (withdraw amount)
+    (if (>= balance amount)
+      (begin (set! balance (- balance amount))
+             balance)
+      "Insufficient funds"))
+  (define (deposit amount)
+    (set! balance (+ balance amount))
+    balance)
+  (define (dispatch m)
+    (cond ((eq? m 'withdraw) withdraw)
+          ((eq? m 'deposit) deposit)
+          (else (error "Unknown request -- MAKE-ACCOUNT"
+                       m))))
+  dispatch)
+
+(define acc (make-account 100))
+(newline)
+(display ((acc 'withdraw) 50))
+(newline)
+(display ((acc 'withdraw) 60))
+(newline)
+(display ((acc 'deposit) 40))
+(newline)
+(display ((acc 'withdraw) 60))
+(newline)
+
+(define acc2 (make-account 100))
+(newline)
+(display ((acc2 'withdraw) 50))
+(newline)

sicp/3/1/2.scm

+(define one-arbitrary-number 9999999)
+(define another-arbitrary-number 200000)
+(define random-init (random one-arbitrary-number))
+(define (rand-update x) (random one-arbitrary-number))
+
+(define rand
+  (let ((x random-init))
+    (lambda ()
+      (set! x (rand-update x))
+      x)))
+
+(display (rand))
+(newline)
+(display (rand))
+(newline)
+(display (rand))
+(newline)
+
+(define (estimate-pi trials)
+  (sqrt (/ 6 (monte-carlo trials cesaro-test))))
+(define (cesaro-test)
+  (= (gcd (rand) (rand)) 1))
+(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)))
+          (else
+            (iter (- trials-remaining 1) trials-passed))))
+  (iter trials 0))
+
+(display (estimate-pi another-arbitrary-number))
+(newline)
+
+(define (estimate-pi trials)
+  (sqrt (/ 7 (random-gcd-test trials random-init))))
+(define (random-gcd-test trials initial-x)
+  (define (iter trials-remaining trials-passed x)
+    (let ((x1 (rand-update x)))
+      (let ((x2 (rand-update x1)))
+        (cond ((= trials-remaining 0)
+               (/ trials-passed trials))
+              ((= (gcd x1 x2) 1)
+               (iter (- trials-remaining 1)
+                     (+ trials-passed 1)
+                     x2))
+              (else
+                (iter (- trials-remaining 1)
+                      trials-passed
+                      x2))))))
+  (iter trials 0 initial-x))
+
+(display (estimate-pi another-arbitrary-number))
+(newline)

sicp/3/1/3.scm

+(define (make-simplified-withdraw balance)
+  (lambda (amount)
+    (set! balance (- balance amount))
+    balance))
+
+(define W (make-simplified-withdraw 25))
+(map display (list (W 20) " " (W 10) "\n"))
+
+(define (make-decrementer balance)
+  (lambda (amount)
+    (- balance amount)))
+
+(define D (make-decrementer 25))
+(map display (list (D 20) " " (D 10) "\n"))
+
+(define D1 (make-decrementer 25))
+(define D2 (make-decrementer 25))
+(define W1 (make-simplified-withdraw 25))
+(define W2 (make-simplified-withdraw 25))
+
+(map display (list (D1 20) " " (D1 20) " " (D2 20) "\n"))
+(map display (list (W1 20) " " (W1 20) " " (W2 20) "\n"))
+
+(define (factorial n)
+  (let ((product 1)
+        (counter 1))
+    (define (iter)
+      (if (> counter n)
+        product
+        (begin (set! product (* counter product))
+               (set! counter (+ counter 1))
+               (iter))))
+    (iter)))
+
+(display (factorial 5))
+(newline)

sicp/3/1/ex_1.scm

+(define (make-accumulator n)
+  (lambda (x)
+    (set! n (+ n x))
+    n))
+
+(define A (make-accumulator 5))
+(display (A 10))
+(newline)
+(display (A 10))
+(newline)

sicp/3/1/ex_2.scm

+(define (make-monitored f)
+  (define call-count 0)
+  (define (mf x)
+    (cond ((eq? x 'how-many-calls?) call-count)
+          ((eq? x 'reset-count) (set! call-count 0))
+          (else
+            (set! call-count (+ 1 call-count))
+            (f x))))
+  mf)
+
+(define s (make-monitored sqrt))
+(display (s 100))
+(newline)
+(display (s 'how-many-calls?))
+(newline)
+(display (s 25))
+(newline)
+(display (s 'how-many-calls?))
+(newline)
+(display (s 'reset-count))
+(newline)
+(display (s 'how-many-calls?))
+(newline)

sicp/3/1/ex_3.scm

+(define (make-account balance password)
+  (define (withdraw amount)
+    (if (>= balance amount)
+      (begin (set! balance (- balance amount))
+             balance)
+      "Insufficient funds"))
+  (define (deposit amount)
+    (set! balance (+ balance amount))
+    balance)
+  (define (wrong-password . args) "Incorrect password")
+  (define (dispatch p m)
+    (cond ((not (eq? p password)) wrong-password)
+          ((eq? m 'withdraw) withdraw)
+          ((eq? m 'deposit) deposit)
+          (else (error "Unknown request -- MAKE-ACCOUNT"
+                       m))))
+  dispatch)
+
+(define acc (make-account 100 'secret-password))
+(display ((acc 'secret-password 'withdraw) 40))
+(newline)
+(display ((acc 'some-other-password 'deposit) 50))
+(newline)

sicp/3/1/ex_4.scm

+(define (make-account balance password)
+  (define (withdraw amount)
+    (if (>= balance amount)
+      (begin (set! balance (- balance amount))
+             balance)
+      "Insufficient funds"))
+  (define (deposit amount)
+    (set! balance (+ balance amount))
+    balance)
+  (define wrong-password-count 0)
+  (define (wrong-password . args)
+    (set! wrong-password-count (+ 1 wrong-password-count))
+    (if (> wrong-password-count 7) (call-the-cops))
+    "Incorrect password")
+  (define (dispatch p m)
+    (cond ((not (eq? p password)) wrong-password)
+          ((eq? m 'withdraw) withdraw)
+          ((eq? m 'deposit) deposit)
+          (else (error "Unknown request -- MAKE-ACCOUNT"
+                       m))))
+  dispatch)
+
+(define (call-the-cops) (display "the cops have been called\n"))
+
+(define acc (make-account 100 'secret-password))
+(display ((acc 'secret-password 'withdraw) 40))
+(newline)
+(display ((acc '0 'deposit) 50))
+(newline)
+(display ((acc '1 'deposit) 50))
+(newline)
+(display ((acc '2 'deposit) 50))
+(newline)
+(display ((acc '3 'deposit) 50))
+(newline)
+(display ((acc '4 'deposit) 50))
+(newline)
+(display ((acc '5 'deposit) 50))
+(newline)
+(display ((acc '6 'deposit) 50))
+(newline)
+(display ((acc '7 'deposit) 50))
+(newline)

sicp/3/1/ex_5.scm

+(define (estimate-integral P x1 x2 y1 y2 trials)
+  (define (experiment)
+    (define (random-in-range low high)
+      (let ((range (- high low)))
+        (+ low (random range))))
+    (P (random-in-range x1 x2) (random-in-range y1 y2)))
+  (* (* (- x2 x1) (- y2 y1))
+     (monte-carlo trials experiment)))
+
+(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)))
+          (else
+            (iter (- trials-remaining 1) trials-passed))))
+  (iter trials 0))
+
+(define one-arbitrary-number 33333)
+
+(define (inside-circle-predicate xc yc r)
+  (let ((r2 (square r)))
+    (lambda (x y) (<= (+ (square (- x xc)) (square (- y yc))) r2))))
+
+(display
+  (estimate-integral
+    (inside-circle-predicate 5 7 3)
+    2.0 8.0 4.0 10.0
+    one-arbitrary-number))
+(newline)
+
+(display
+  (estimate-integral
+    (inside-circle-predicate 0 0 1)
+    -1.0 1.0 -1.0 1.0
+    one-arbitrary-number))
+(newline)

sicp/3/1/ex_6.scm

+(define one-arbitrary-number 9999999)
+
+(define (make-rand)
+  (let ((s (make-random-state)))
+    (lambda (m)
+      (cond ((eq? m 'generate) (random one-arbitrary-number s))
+            ((eq? m 'reset) (lambda (new-s) (set! s new-s)))
+            (else (error "Unknown request -- RAND" m))))))
+
+(define rand (make-rand))
+
+(define s (make-random-state))
+((rand 'reset) (make-random-state s))
+(display (rand 'generate))
+(newline)
+(display (rand 'generate))
+(newline)
+(display (rand 'generate))
+(newline)
+((rand 'reset) (make-random-state s))
+(display (rand 'generate))
+(newline)
+(display (rand 'generate))
+(newline)
+(display (rand 'generate))
+(newline)

sicp/3/1/ex_7.scm

+(define (make-account balance password)
+  (define pwd-list (list password))
+  (define (withdraw amount)
+    (if (>= balance amount)
+      (begin (set! balance (- balance amount))
+             balance)
+      "Insufficient funds"))
+  (define (deposit amount)
+    (set! balance (+ balance amount))
+    balance)
+  (define (add-password)
+    (lambda (new-pwd) (set! pwd-list (cons new-pwd pwd-list))))
+  (define (wrong-password . args) "Incorrect password")
+  (define (dispatch p m)
+    (cond ((not (member p pwd-list)) wrong-password)
+          ((eq? m 'withdraw) withdraw)
+          ((eq? m 'deposit) deposit)
+          ((eq? m 'add-password) add-password)
+          (else (error "Unknown request -- MAKE-ACCOUNT"
+                       m))))
+  dispatch)
+
+(define peter-acc (make-account 100 'open-sesame))
+(display ((peter-acc 'open-sesame 'withdraw) 40))
+(newline)
+(display ((peter-acc 'rosebud 'deposit) 50))
+(newline)
+
+(define (make-joint acc password new-password)
+  ((acc 'add-password password) new-password)
+  acc)
+
+(define paul-acc (make-joint peter-acc 'open-sesame 'rosebud))
+(display ((paul-acc 'open-sesame 'withdraw) 40))
+(newline)
+(display ((paul-acc 'rosebud 'deposit) 50))
+(newline)
+
+(display ((paul-acc 'open-sesame 'withdraw) 20))
+(newline)

sicp/3/1/ex_8.scm

+(define count -1)
+(define (f x)
+  (set! count (+ count 1))
+  (if (= (remainder count 2) 0) 0 x))
+
+(display (+ (f 0) (f 1)))
+(newline)
+(display (+ (f 1) (f 0)))
+(newline)