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