Working Through SICP Exercises

As I work through SICP exercises, I will post them there.

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SICP Exercise 1.22 search-for-primes

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Exercise 1.22.    Most Lisp implementations include a primitive called  runtime  that returns an integer that specifies the amount of time the system has been running (measured, for example, in microseconds). The following  timed-prime-test  procedure, when called with an integer  n , prints  n  and checks to see if  n  is prime. If  n  is prime, the procedure prints three asterisks followed by the amount of time used in performing the test. (define (timed-prime-test n)   (newline)   (display n)   (start-prime-test n (runtime))) (define (start-prime-test n start-time)   (if (prime? n)       (report-prime (- (runtime) start-time)))) (define (report-prime elapsed-time)   (display " *** ")   (display elapsed-time)) Using this procedure, ...
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SICP Exercise 4.9 do for while until

Exercise 4.9.    Many languages support a variety of iteration constructs, such as  do ,  for ,  while , and  until . In Scheme, iterative processes can be expressed in terms of ordinary procedure calls, so special iteration constructs provide no essential gain in computational power. On the other hand, such constructs are often convenient. Design some iteration constructs, give examples of their use, and show how to implement them as derived expressions. SOLUTION The code and tests are  here . I have implemented the following expressions: do-while do-until for while The 'do-while' construct can be as follows: (do   (<one or more statements>)   while (condition) ) Use the while block construct to convert it as follows: (begin   <statements>   (while (condition)   <statements>   ) ) The 'do-until' construct can be as follows: (do   (<one or more statements>) ...
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SICP Exercise 3.45 deadlock

Exercise 3.45.   Louis Reasoner thinks our bank-account system is unnecessarily complex and error-prone now that deposits and withdrawals aren't automatically serialized. He suggests that  make-account-and-serializer  should have exported the serializer (for use by such procedures as  serialized-exchange ) in addition to (rather than instead of) using it to serialize accounts and deposits as  make-account  did. He proposes to redefine accounts as follows: (define (make-account-and-serializer balance)   (define (withdraw amount)     (if (>= balance amount)         (begin (set! balance (- balance amount))                balance)         "Insufficient funds"))   (define (deposit amoun...
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