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notes14s - 6 8 10 6 8 2 Write a function an-atom-of that...

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CS61A Notes 14 – Your Father’s Worst Nightmare [Solutions v1.0] Of Pills And Other Euphoric Items QUESTIONS: What is printed at each line? 1. > (define x (+ 2 3)) > x ==> 5 > (define y ((lambda(a) a) (* 3 4))) > y ==> 12 > (define z ((lambda(b) (+ b 10)) y)) > z ==> 22 Note that, without mutation or assignment, lazy evaluation works just like normal STk. 2. > (define count 0) > (define (foo x y) (x y)) > (define z (foo (lambda(a) (set! count a) (* a a)) (begin (set! count (+ 1 count)) count))) > count ==> 0 > z ==> infinite loop (doh!) 3. > (define count 0) > (define (incr!) (set! count (+ count 1))) > (define (foo x) (let ((y (begin (incr!) count))) (if (<= count 1) (foo y) x) > (foo 10) ==> infinite loop Nondeterministic and Indecisive QUESTIONS 1. Suppose we type the following into the amb evaluator: > (* 2 (if (amb #t #f #t) (amb 3 4) 5)) What are all possible answers we can get?
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Unformatted text preview: 6, 8, 10, 6, 8 2. Write a function an-atom-of that dispenses the atomic elements of a deep list (not including empty lists). For example, > (an-atom-of ‘((a) ((b (c))))) ==> a > try-again ==> b (define (an-atom-of ls) (cond ((null? ls) (amb)) ((atom? ls) ls) (else (amb (an-atom-of (car ls)) (an-atom-of (cdr ls)))))) Chung Wu; CS61A, Spring 2004 1 3. Use an-atom-of to write deep-member? . (define (deep-member? X ls) (let ((maybe-x (an-atom-of ls))) (require (equal? x maybe-x)) #t)) 4. Fill in the blanks: > (define (choose-member L R) (cond ((null? R) (amb)) ((= (car L) (car R)) (car L)) (else (amb (choose-member L (cdr R)) (choose-member (cdr L) R))))) > (choose-member ‘(1 2 3) ‘(4 2 3)) 3 > try-again 2 > try-again 2 Chung Wu; CS61A, Spring 2004 2...
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