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category-theory-presentation/categories/30_How/300_Catamorphisms/060_morphism_missing_information_retrieved.md
Yann Esposito (Yogsototh) 60135c8697 initial commit see my ykeynote repo for history
2013-02-28 16:49:12 +01:00

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κατα-morphism: missing information retrieved

type Algebra f a = f a -> a
instance Functor (StrF a) =
	fmap f (Cons c x) = Cons c (f x)
	fmap _ Nil = Nil

cata :: Functor f => Algebra f a -> Mu f -> a
cata f = f . fmap (cata f) . outF