Recursion schemeという、foldr、unfoldrを一般化した概念があるらしいのでHaskellで色々実装してみた。あとchronomorphismのかっこよさは異常(←しつこい)。 {-# LANGUAGE StandaloneDeriving, UndecidableInstances #-} import Control.Monad import Control.Monad.Free import Control.Comonad import Control.Comonad.Cofree newtype Fix f = Fix (f (Fix f)) unfix (Fix f) = f deriving instance Show (f (Fix f)) => Show (Fix f) -- morphisms hylo :: Functor f => (f b ->
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