nasty things possible with generalized newtype deriving

Wolfgang Jeltsch g9ks157k at
Tue Mar 9 04:44:21 EST 2010

Hello guys,

are you following this Haskell Cafe thread:


Seems that you can do ugly things with GHC’s current implementation of 
generalized newtype deriving. For example, you can easily construct sets with 
corrupted internal structure even if there are no bogus Ord instances.

Best wishes,

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