> Do you have a kind * implementation of Foldable? I'd be interested in
> seeing it, because I was unable to create a usable implementation (based
> upon the RMonad scheme) on my last attempt.
I was going to make it a subset of Foldable: fold, foldr, foldl, etc.
So you don't have a working implementation yet? I ended up thinking this is impossible, although I don't remember the reasoning that led me to that conclusion (and I could very well be wrong).
I would suggest that you check this before going too far along the restricted-monad path.
John