On Mar 14, 2012, at 3:53 AM, Roelof Wobben wrote: > Hello, > > I have to make a function which do nothing with the special key's. > According to the manual I can use this : > > > Here is a typical key-event handler: > (define (change w a-key) > (cond > [(key=? a-key "left") (world-go w -DELTA)] > [(key=? a-key "right") (world-go w +DELTA)] > [(= (string-length a-key) 1) w] ; order-free checking > [(key=? a-key "up") (world-go w -DELTA)] > [(key=? a-key "down") (world-go w +DELTA)] > [else w])) > > But Can I use this if I want that if a special-key is used nothing happens. > > > [key?a-key "/t") ()] >
You need to complete the phrase "nothing happens" and then you will see how you went wrong: "nothing happens to the world". You should also look at the signature of this function, which is World -> World i.e. it always takes a world and returns one (possibly a different one than it got or the same one). ____________________ Racket Users list: http://lists.racket-lang.org/users
