; list homework (define (len xs) (if (null? xs) 0 (+ (len (cdr xs)) 1))) (display (len '(1 2 3 4 5))) (newline) (define (len-aux xs len) (if (null? xs) len (len-aux (cdr xs) (+ len 1)))) (define (len xs) (len-aux xs 0)) (display (len '(1 2 3 4 5))) (newline) (define (rev-aux xs zs) (if (null? xs) zs (rev-aux (cdr xs) (cons (car xs) zs)))) (define (rev xs) (rev-aux xs '())) (display (rev '(1 2 3 4 5))) (newline)