Why is there no Foldable instance for Either?

[Henning Thielemann]

On Thu, 30 May 2013, Gabriel Gonzalez wrote:

> This came up in the context of an issue raised on the `errors` package:
>
> https://github.com/Gabriel439/Haskell-Errors-Library/issues/16
>
> I could provide an orphan instance for `Either` in the `errors` package, but 
> I wanted to ask if it was possible to incorporate the instance directly into 
> `Data.Foldable`.

For my taste it is abuse to use Either for handling exceptions, thus it 
would be more abuse to support that with a Foldable instance.