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POReal-world applications of zygohistomorphic prepromorphisms
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copied!<p>Yes, <a href="http://www.haskell.org/haskellwiki/Zygohistomorphic_prepromorphisms" rel="nofollow noreferrer">these ones</a>:</p> <pre><code>{-#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)) </code></pre> <p>Yes, I know that they're a (<a href="http://www.catb.org/jargon/html/H/ha-ha-only-serious.html" rel="nofollow noreferrer">HHOS</a>) 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 <em>will</em> 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 <a href="http://www.reddit.com/r/programming/comments/6ml1y/a_pretty_useful_haskell_snippet/c04ako5" rel="nofollow noreferrer">short explanation</a> on reddit.</p> <p>Eligible Answers must:</p> <ol> <li><p>do something at least remotely and theoretically computationally useful. That is, answers that reduce to <code>id</code> are out.</p></li> <li><p>use all the features of the scheme, no passing in of id, or const, or equivalent.</p></li> <li><p>not equally well be expressible by a simple, vanilla fold or such, so don't merely implement <code>product</code> in a meandering way.</p></li> </ol> <p>Bonus points will be given to:</p> <ul> <li><p>Well-known problem or algorithm</p></li> <li><p>solved, respectively expressed, in an unusual way that gains</p></li> <li><p>clarity and/or performance</p></li> <li><p>and/or hack value</p></li> <li><p>and/or lulz, in roughly that order, as well as</p></li> <li><p>high-ranking answers (yay democracy)</p></li> </ul> <p>Please also note <a href="https://stackoverflow.com/questions/5057136/real-world-applications-of-zygohistomorphic-prepromorphisms/5058725#5058725">Edward's answer</a> below. What ZHPM implementation you use is your choice.</p>

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