(define-struct dir (name contents))

(defile (file? any)
  (symbol? any))

;;;;;;;;;;;;;;;;;;;;;;;;

; flatten-dir : directory symbol -> (directory or l-o-d-f)
; removes the named subdirectory, moving its contents up one level
(define (flatten-dir a-dir name)
  (cond
    [(symbol=? (dir-name a-dir) name)
     (dir-contents a-dir)]
    [else
     (make-dir (dir-name a-dir)
               (flatten-dir-in-lodf (dir-contents a-dir) name))]))

; flatten-dir-in-lodf : l-o-d-f symbol -> l-o-d-f
; removes the named subdirectory, moving its contents up one level
(define (flatten-dir-in-lodf a-lodf name)
  (cond
    [(empty? a-lodf)        empty]
    [(file? (first a-lodf)) (cons (first a-lodf)
				  (flatten-dir-in-lodf (rest a-lodf) name))]
    [(dir? (first a-lodf))  (flatten-helper
			      (flatten-dir (first a-lodf) name)
			      (flatten-dir-in-lodf (rest a-lodf) name))]))

; flatten-helper : (directory or l-o-d-f) l-o-d-f -> l-o-d-f
; combines (an item or list) and a list into a new list
(define (flatten-helper a-dir-or-lodf a-lodf)
  (cond [(dir? a-dir-or-lodf) (cons a-dir-or-lodf a-lodf)]
	[else                 (append a-dir-or-lodf a-lodf)]))