[Haskell-beginners] Heterogeneous Lists

Every OO language which supports generics allows a declaration such as List<Show> alist, where Show is an interface. Any type implementing Show can be put in alist, and any Show operation can be performed on the alist's members. No casts, wrappers, or other special types and plumbing are needed. Why isn't it possible to do this directly in Haskell?