[racket] How to use abstract classes?

From: Alexander Kasiukov (kasiuka at sunysuffolk.edu)
Date: Wed Aug 24 10:31:00 EDT 2011

Dear Racket users,

What is the best way to make a class in Racket abstract? I would like to 
have a class which

     never gets instantiated
     implements certain methods common to all of its children
     needs to call some of the methods implemented in the children.

Sincerely yours,

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