[plt-scheme] box contract

From: Mike T. Machenry (dskippy at ccs.neu.edu)
Date: Wed Jul 24 15:22:59 EDT 2002

Is there a proper way to contract a box to be a specific type of box?

;;i could easily contract it as such
  (number-changer (box? . -> . void?)))

;;this has more desirable expresability
  (number-changer ((box-of number?) . -> . void?)))


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