1 665c255d 2023-08-04 jrmu 
 2 665c255d 2023-08-04 jrmu Exercise 3.52.  Consider the sequence of expressions
 3 665c255d 2023-08-04 jrmu 
 4 665c255d 2023-08-04 jrmu (define sum 0)
 5 665c255d 2023-08-04 jrmu (define (accum x)
 6 665c255d 2023-08-04 jrmu   (set! sum (+ x sum))
 7 665c255d 2023-08-04 jrmu   sum)
 8 665c255d 2023-08-04 jrmu (define seq (stream-map accum (stream-enumerate-interval 1 20)))
 9 665c255d 2023-08-04 jrmu (define y (stream-filter even? seq))
10 665c255d 2023-08-04 jrmu (define z (stream-filter (lambda (x) (= (remainder x 5) 0))
11 665c255d 2023-08-04 jrmu                          seq))
12 665c255d 2023-08-04 jrmu (stream-ref y 7)
13 665c255d 2023-08-04 jrmu (display-stream z)
14 665c255d 2023-08-04 jrmu 
15 665c255d 2023-08-04 jrmu What is the value of sum after each of the above expressions is evaluated? What is the printed response to evaluating the stream-ref and display-stream expressions? Would these responses differ if we had implemented (delay <exp>) simply as (lambda () <exp>) without using the optimization provided by memo-proc ? Explain.