Personal tools

Zygohistomorphic prepromorphisms

From HaskellWiki

(Difference between revisions)
Jump to: navigation, search
m (Error in the use of « à la » (« la » is more or less the French for « the »))
 
Line 8: Line 8:
 
import Control.Functor.Extras
 
import Control.Functor.Extras
   
zygohistomorphic_prepromorphism :: Functor f => Algebra f b -> GAlgebra f (Cofree f) a -> (f :~> f) -> FixF f -> a
+
zygoHistoPrepro
zygohistomorphic_prepromorphism f = g_prepro (distZygoT (liftAlgebra f) (distHisto id))
+
:: (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.
 
-- unless you want a generalized zygomorphism.
 
</pre>
 
</pre>

Latest revision as of 21:03, 20 February 2011

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.