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Computer Science 61A - Fall 1997 - Harvey - Midterm 3

# Computer Science 61A - Fall 1997 - Harvey - Midterm 3 - CS...

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CS 61A, Midterm #3, Fall, 1997 CS 61A, Fall 1997 Midterm 3 Professor Harvey Problem #1 What will the Scheme interpreter print in response to each of the following expressions? Also, draw a "box and pointer" diagram for the result of each expression. Hint: It'll be a lot easier if you draw the box and pointer diagram first! (let ((x (list 1 2 3 4))) (set-cdr! x (cdr x)) x) (let ((x (list 1 2 3 4))) (set-car! (cddr x) (cdr x)) x) (let ((x (list 1 2 3 4))) (set-cdr! (cdr x) (cadr x)) x) Problem #2 An improper list is a data structure made of pairs, in which the cdr of some pair is anything other than a pair or the empty list. Write the procedure deep-fix! that takes a pair as its argument, examines the data structure headed by that pair, and replaces any improper cdr with the empty list. For example: > (deep-fix! '(1 2 (3 4 .5) (6 (7 . 8) 9) 10 . 11)) (1 2 (3 4) (6 (7) 9) 10) (In the example I've broken the rule about not mutating quoted data, in order to make the example easier for you to read.) NOTE: Do not allocate any new pairs in your solution. Modify the existing pairs.

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