Proposal: Add a few extra members to Foldable and Traversable classes

[Henning Thielemann]

On Fri, 19 Sep 2014, David Feuer wrote:

> Joachim, you may be right about sum and product; I really don't know. 
> Henning: this doesn't change the Data.Foldable API at all. Data.Foldable 
> already exports all of these functions, and the class would give each of 
> them a valid default implementation.

For consumers of the functions it would not change much. However, user 
instances with custom implementations of the new methods cannot be used 
with older Prelude versions anymore.