Structure and Interpretation of Computer Programs by Harold Abelson & Gerald Jay Sussman & Julie Sussman

Author:Harold Abelson & Gerald Jay Sussman & Julie Sussman
Language: eng
Format: epub
ISBN: 0-262-01153-0
Publisher: MIT Press

(define x (stream-map show (stream-enumerate-interval 0 10)))

(stream-ref x 5)

(stream-ref x 7)

Exercise 3.52. Consider the sequence of expressions

(define sum 0)

(define (accum x)

(set! sum (+ x sum))

sum)

(define seq (stream-map accum (stream-enumerate-interval 1 20)))

(define y (stream-filter even? seq))

(define z (stream-filter (lambda (x) (= (remainder x 5) 0))

seq))

(stream-ref y 7)

(display-stream z)

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.

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