[Haskell-cafe] Usage of rewrite rule specialization in Hackage

I'm looking for "real" code that uses the kind of GHC rewrite rule that specializes a polymorphic function with another one, as described here <http://www.haskell.org/ghc/docs/latest/html/users_guide/rewrite- rules.html#rule-spec>. Can anyone point me to any popular packages in Hackage that make use of this? Thanks, Scott