# Difference between revisions of "Zygohistomorphic prepromorphisms"

From HaskellWiki

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import Control.Morphism.Histo |
import Control.Morphism.Histo |
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import Control.Functor.Algebra |
import Control.Functor.Algebra |
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+ | import Control.Functor.Extras |
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zygohistomorphic_prepromorphism :: Algebra f b -> GAlgebra f (Cofree f) a -> (f :~> f) -> FixF f -> a |
zygohistomorphic_prepromorphism :: Algebra f b -> GAlgebra f (Cofree f) a -> (f :~> f) -> FixF f -> a |

## Revision as of 01:39, 9 June 2008

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 ala a paramorphism.

import Control.Morphism.Zygo import Control.Morphism.Prepro import Control.Morphism.Histo import Control.Functor.Algebra import Control.Functor.Extras zygohistomorphic_prepromorphism :: Algebra f b -> GAlgebra f (Cofree f) a -> (f :~> f) -> FixF f -> a zygohistomorphic_prepromorphism f = g_prepro (distZygoT (liftAlgebra f) (distHisto id)) -- unless you want a generalized zygomorphism.