[Haskell-beginners] Editor choices

Greetings, So I find myself playing around with XMonad source code. I'm a long time Vim user and I've made a tags file to help me navigate the source code. I've got decent syntax highlighting. What I lack is insight into the libs. I'd like the editor/IDE to tell me the type of a thing, or at least the module it is defined in. Is this a sensible question for haskell? I just don't want to have to hunt for where lib functions are defined (tags take me around the xmonad sources with drama). So what editors/IDEs to people use for haskell to help with this? Or do you all just keep everything in your massive brains? :-) Cheers, Jeff