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.