foo.rkt

;; a note is (make-note note-num frames frames)
(define-struct note (pitch time duration))

;; number -> number
;; converts seconds to frames
(define (s f)
  (* 44100 f))

(check-expect (s 10) 441000)

;; list-of-notes -> list-of-notes 
;; returns all notes that end in first 10 sec
(define (ten-sec l)
  (cond [(empty? l) empty]
        
        [(<= (+ (note-duration (first l)) (note-time (first l))) 
             (s 10))
         (cons (first l) (ten-sec (rest l)))]
        
        [else (ten-sec (rest l))]))

(check-expect (ten-sec
               (cons (make-note 60 4410000 25)
                     (cons (make-note 60 44000 25)
                           empty)))
              (cons (make-note 60 44000 25)
                    empty))