On Mon, Mar 9, 2015 at 10:33 PM, Rustom Mody <rustompmody@gmail.com> wrote:

My impression is that earlier
[] == []

used to give a type error.  Now it gives True.

So

1. Which instance of == is being used?

2. Is there some option controlling this behavior?

The instance being used is (), and it's controlled by -XExtendedDefaultRules.

https://downloads.haskell.org/~ghc/latest/docs/html/users_guide/interactive-evaluation.html#extended-default-rules