anchor.diff:  
   For reference, the Haskell recursive quicksort looks like this:
   
  -[code,haskell]
  +[source,haskell]
   ----
   quicksort :: (Ord a) => [a] -> [a]
   quicksort [] = []
  
positive.code: To be able to get a similarly powerful, if not as convenient function,
  we have to upgrade our Racket version a bit:
  
  [code,scheme]
  ----
  (define (qs-2 fun lst)
    (if (empty? lst)
  
negative.code: quicksort can readily handle numbers, strings, or lists of chars, all
  thanks to the power of this line right here:
  
  [source,haskell]
  ----
  quicksort :: (Ord a) => [a] -> [a]
  ----
  