[Haskell-cafe] self-referential data

From https://secure.wikimedia.org/wikipedia/en/wiki/Bencoding , I think I should code

data BValue = BString String | BInteger Integer | BList [BValue] | BDictionary (M.Map BString BValue) but: Not in scope: type constructor or class `BString' The implementations I've found just implemented BDictionary's map key as String, but I think that's kind of wrong.