On May 28, 2013, at 12:36 AM, harry <voldermort@hotmail.com> wrote:

> 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?

My impression is that you often don't have this requirement, since functions are first-class values and you can treat them as closures.