Yes, these ones:

{-#LANGUAGE TypeOperators, RankNTypes #-} import Control.Morphism.Zygo import Control.Morphism.Prepro import Control.Morphism.Histo import Control.Functor.Algebra import Control.Functor.Extras import Control.Functor.Fix import Control.Comonad.Cofree zygohistomorphic_prepromorphism :: Functor f => Algebra f b -> GAlgebra f (ZygoT (Cofree f) b) a -> (f :~> f) -> FixF f -> a zygohistomorphic_prepromorphism f = g_prepro (distZygoT (liftAlgebra f) (distHisto id))

Yes, I know that they're a (HHOS) joke. I'm looking for a real-world example for simple hack value and last, but not least, to add it to the wiki saying "This is the idiomatic way to express XYZ". I will put a bounty on this should you fail to come up with a solution. If you're completely lost on what they're about, Edward posted a short explanation on reddit.

Eligible Answers must:

do something at least remotely and theoretically computationally useful. That is, answers that reduce to id are out. use all the features of the scheme, no passing in of id, or const, or equivalent. not equally well be expressible by a simple, vanilla fold or such, so don't merely implement product in a meandering way.

Bonus points will be given to:

Well-known problem or algorithm

solved, respectively expressed, in an unusual way that gains

clarity and/or performance

and/or hack value

and/or lulz, in roughly that order, as well as

high-ranking answers (yay democracy)

Please also note Edward's answer below. What ZHPM implementation you use is your choice.