"panic! (the `impossible' happened): " again

[George Russell]

Glasgow Haskell seems to be good at doing the impossible . .  .

panic! (the `impossible' happened):
        mkWWcpr: not a product
    w{-rIZ-}
    -> e{-rJ1-}
    -> Listener.DispatchMode{-rgO,i-}
    -> ExternalEvent.IA{-rgh,i-} GUIEvent.EventInfo{-rsx,i-}

Let me know if you want the source file and all constituent .hi files . . .