moving Foldable and Traversable to Prelude

[Henning Thielemann]

On Wed, 15 May 2013, David Luposchainsky wrote:

> +1. I think the Prelude should be a general module of the most commonly
> needed functions, which (generalized) folds and traversals are certainly
> part of; right now it feels more like a beginner module at times.

It is certainly a kind of beginner module, but that's good. Experts know 
how to import. Putting the most general functions into Prelude does not 
work because:

1. There are often multiple sensible generalizations of a Prelude 
function.

2. You have to add more type annotations since types cannot be infered 
from the functions.


There is simply no need to change Prelude and all packages that rely on 
specific types. Just don't be lazy and import the stuff you need!

I should change my vote to:

  -10