(define win appletwin)
(define TT (textfield "Hello, world!" 30))
(define butt (button "push here to see the author"))
(add (box(box(col TT butt))) win)
(validate win)
(show win)
(define (flash N)
          (write TT "The author is Yan Luo")
          (sleep 1000)
          (write TT "")
          (sleep 500)
          (if (> N 0) (flash (- N 1))
              (seq (write TT "Hello, world!")
                   (write butt "push here to see the author"))
          )
)
(define (s) (write butt "It will stop after 11 flashes")(flash 10))
(addCallback butt s win)