"Haxl users at Facebook do a lot of development and testing inside GHCi. In fact, we’ve built a customized version of GHCi that runs code in our Haxl monad by default instead of the IO monad, and has a handful of extra commands to support common workflows needed by our developers."
https://github.com/ndmitchell/ghcid http://neilmitchell.blogspot.de/2014/09/ghcid-new-ghci-based...