Question

In racket, Given the function definition:

(define (guess   a_list)                                     

    (if (null? a_list)

   0

   (+ 1 (guess (cdr a_list)))

))

(a) write the derivation of the following function call:  (guess ‘(3 1 2 5)) =>

(b) explain what this function is doing when given a parameter a_list (NOT the steps of execution, but the result).

Answer 1

Solution:

Given function definition:

(define (guess   a_list)                                     

    (if (null? a_list)

   0

   (+ 1 (guess (cdr a_list)))

))

a.Ans:

(guess ‘(3 1 2 5))

= 1 + (guess (1 2 5))

= 1 + 1 + (guess (2 5))

= 1 + 1 + 1 + (guess (5))

= 1 + 1 + 1 + 1 + (guess ())

= 1 + 1 + 1 + 1 + 0

= 4

b.Ans:

(guess ‘(3 1 2 5))

calls the guess function here the list is [3 1 2 5]

if the list is empty then return 0

else add 1 to the recursive guess function until the list becomes 0

Finally the result will be 4 as there are 4 elements in the list.