Haskell Foldable Wats

[Henning Thielemann]

On Wed, 24 Feb 2016, Manuel Gómez wrote:

> To avoid this unhelpful outcome, if the community decided to forbid
> these instances, some language extension would have to be designed to
> forbid instance definitions.  This has been discussed previously.

It's possible to achieve this without language extensions.

>  If the community did this, it would break a lot of code that does use 
> these instances, and there would be no workaround,

The backwards-compatible work-around would be simple: Don't use fmap, but 
mapThd3 and friends.

It would be a good opportunity to cleanup code.