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 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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SICP Exercise 4.18 a alternative strategy for interpreting internal definitions

Exercise 4.18.   Consider an alternative strategy for scanning out definitions that translates the example in the text to (lambda < vars >   (let ((u '*unassigned*)         (v '*unassigned*))     (let ((a < e1 >)           (b < e2 >))       (set! u a)       (set! v b))     < e3 >)) Here  a  and  b  are meant to represent new variable names, created by the interpreter, that do not appear in the user's program. Consider the  solve  procedure from section  3.5.4 : (define (solve f y0 dt)   (define y (integral (delay dy) y0 dt))   (define dy (stream-map f y))   y) Will this ...
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