Buggy Quicksort

;;
; partition
; ---------
; Takes in a list and a pivot value
; Returns the list split into two parts:
;     1) All elements <= p (but not including that specific p)
;     2) All elements > p
(define (partition lst p) (list
                               (append
                                (filter (lambda (n) (< n p)) lst)
                                (cdr (filter (lambda (n) (= n p)) lst)))
                               (filter (lambda (n) (> n p)) lst)))

;;
; quicksort
; ---------
; Quicksort implementation
(define (quicksort lst)
  (cond ((null? lst) lst) ; If the list is empty, return
        ((null? (cdr lst)) lst) ; If the list is a singleton, return
        (else (flatten (list ; Otherwise, return a new list, choosing a pivot value of (car lst)
                        (quicksort (car (partition lst (car lst)))) ; with the quick-sorted left side
                        (car lst) ; the pivot value
                        (quicksort (cdr (partition lst (car lst)))) ; and the quick-sorted right side
                        )
              )
        )
  )
)