From the description: "This means that being r = result, r^n = x;"

is not really clear. Waybe reword to (root x n)^n = x?

The description of the kata is all messed up.

Isn't there are some issues with writing an instance of Ord like this? Some hands will be tied according to Poker rules, and I guess EQ will be returned in those cases. However, this means that the Ord instance will not be a total order (indeed, not even a partial order). This means that you can't store hands realiably in a container relying on Ord, e.g. Data.Map or Data.Set.

It feels a bit clunky to have a fold function that takes seven functions. But you are of course correct.

The function called "i" in the text and code should be named "l", since this is what the test expects.

Sounds like a great idea!

Maybe. On the other hand, it is meant to be easy.

Absolutely, thank you.

Thank you for your feedback ajnsit. I have added a link to HaskellWiki about newtype. However, I do not see the point of the hiding the declaration; you would never have that situation when actually programming.

This seems really interesting to me, but I am not sure I grasp all the language features used here.
I think one of the major stumbling blocks for me is the line:
type Term a = forall r h . Language r => r h a

What does this mean? Is there maybe a Haskell wiki page that can be linked to explain this?
Maybe the author wants the user to find this by him- or herself, in which case it is of course fine, but I think that if you want people to learn from this, some basic links could wouldn't hurt.

What should happen with a singleton list?