[racket] Error Message

Hello, 

Whenever, I try to create a Gui I keep getting "read: illegal use of open square bracket” for the following code: 

; Make a frame by instantiating the frame% class
(define frame (new frame% [label "Example"]))
 
; Show the frame by calling its show method
(send frame show #t)


I am using racket 6.0 

Thanks, KK 
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