From HaskellWiki

Used when you really need both semi-mutual recursion and history and to repeatedly apply a natural transformation as you get deeper into the functor. Zygo implements semi-mutual recursion like a zygomorphism. Para gives you access to your result à la paramorphism.

import Control.Morphism.Zygo import Control.Morphism.Prepro import Control.Morphism.Histo import Control.Functor.Algebra import Control.Functor.Extras zygoHistoPrepro :: (Unfoldable t, Foldable t) => (Base t b -> b) -> (forall c. Base t c -> Base t c) -> (Base t (EnvT b (Stream (Base t)) a) -> a) -> t -> a zygoHistoPrepro f g t = gprepro (distZygoT f distHisto) g t -- unless you want a generalized zygomorphism.