Write a scheme function named longer-list that takes two list arguments and retu

Question

Write a scheme function named longer-list that takes two list arguments and returns the longer list of the two inputs. If the two lists are equal in length, the function returns #t, and if one of the arguments is not a list, the function should return #f.

Note: You are not allowed to use the predefined length function; however, you can write your version of length or other helper functions that you may want to call from longer-list.

Sample runs:

(longer-list '(1 2 3 4) '(a b c d e)) returns (a b c d e)

(longer-list '(d e f) '(4 5 6)) returns #t (or true)

(longer-list '(g h i) 3) returns #f (or false)

Explanation / Answer

(define (longer-list x y)

(and (list? x)

       (list? y)

       (let ll ((xx x) (yy y))

         (cond          

           ((and (null? xx) (null? yy)) #t)

           ((null? xx) y)

           ((null? yy) x)

           (else (ll (cdr xx) (cdr yy)))))))

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