Hi everybody! I have just released a handy package on Hackage that will interest you if you've ever used unordered-containers with a custom type. In order to do such a thing, you'd need to define an instance of Hashable. This process could easily be automated. And so I did. {-# LANGUAGE DeriveGeneric #-} module ThisIsPrettyNeat where import Data.Hashable.Generic import GHC.Generics data MyCoolType a = MCT0 | MCT1 (Either Int a) | MCT2 (MyCoolType a) (MyCoolType a) deriving Generic instance Hashable a => Hashable MyCoolType where hashWithSalt s x = gHashWithSalt s x {-# INLINEABLE hashWithSalt #-} and voila. You have a very performant instance of Hashable, with minimal boilerplate, no template haskell, and no subtle bugs. If you want to play with it, here it is: http://hackage.haskell.org/package/hashable-generics-1.1.6 Have fun! - Clark Oh yeah, and if anyone wants to help me figure out why it's 1.3x slower than my hand-rolled instances, that would be really helpful.