(define (mode L)
   (mode-helper '() L))

(define (mode-helper run L)
 (define (next-run L)
     (if    (and (list? (cdr L)) (equal? (car L) (cadr L)))
;;the list test is to make sure
;;cadr will not return an error
        (cons (car L) (next-run (cdr L)))
        (cons (car L) '())))
  (cond ((null? L) run)
    ((> (count (next-run L)) (count run))
     (mode-helper (next-run L) (cdr L)))
    (else (mode-helper run (cdr L)))))
;;here (cdr L) could be (but-next-run L (next-run L)
;;return the cdr of both until (next-run L) is null
;;the make the function more effecient
;;also you could use a let to avoid calulation (next-run L)
;;multiple times

(define (count L)
    (if (null? L)
    0
    (+ 1 (count (cdr L)))))

(mode '(1 2 2 3 3 3 4))