That is already how it's defined in the `base` package right now though: class Eq a where (==), (/=) :: a -> a -> Bool x /= y

That is already how it's defined in the `base` package right now though: class Eq a where (==), (/=) :: a -> a -> Bool x /= y = not (x == y) x == y = not (x /= y) https://www.stackage.org/haddock/lts-18.17/ghc-prim-0.6.1/src/GHC-Classes.html#Eq https://www.stackage.org/haddock/lts-18.17/ghc-prim-0.6.1/sr... The way this works is that when you implement the `Eq` typeclass for a type, you can provide more specific implementations. A minimal complete implementation is to implement either == or /= for your type, and the other definition will apply. The way this breaks existing code (iiuc) is that as a top-level function, if you have imported the `Eq` type class but haven't imported the `Prelude` module implicitly (on by default but can be turned off), you will not have `/=` in scope anymore. I think people are upset by this less because of how hard it would be to fix, but more because of how it acts as a sort of signaling change ("they're willing to break my code for this, which I didn't want, but not for X which I did"). The most common value of X I've seen is removing or reworking the partial functions in the Prelude (e.g., head / tail on `[a]` raising an exception instead of returning `Maybe a`).