Reading the other thread (Adding Applicative/Functor instances to all Monads in GHC) I was wondering if there was infrastructure for testing what effect making the often-discussed Functor/Monad change would have: How many packages on hackage would break etc. I have read a few times that people have "compiled all of hackage" to see the impact of whatever. How do you do that? Do you just run a loop around cabal install or have you built some more advanced tools to visualize the results better or compile the packages "from ground up", in order of their dependencies? I'm interested in anything in this direction.