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🔥 CVAlgebra handling.

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We run the risk of making paramorphisms quadratic if we use histomorphisms to decorate, so we compromise on the added flexibility.
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Rob Rix 2017-04-25 12:10:48 -04:00
parent 2b703d1f31
commit 7bf60eb2ff
1 changed files with 1 additions and 15 deletions
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16
src/Language/Ruby/Syntax.hs
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@ -1,7 +1,7 @@
{-# LANGUAGE DataKinds, GeneralizedNewtypeDeriving, TemplateHaskell, TypeOperators #-}
module Language.Ruby.Syntax where
import Data.Functor.Foldable (Base, Corecursive(..))
import Data.Functor.Foldable (Base)
import Data.Functor.Union
import Data.Record
import qualified Data.Syntax as Syntax
@ -115,24 +115,10 @@ type FAlgebra f a = f a -> a
-- | An R-algebra on some carrier functor 'f' of its fixpoint type 't'.
type RAlgebra f t a = f (t, a) -> a
-- | A CV-algebra (Course of Value) on some carrier functor 'f'; an algebra which provides its references upon request.
type CVAlgebra f a = f (Cofree f a) -> a
-- | Promote an FAlgebra into an RAlgebra (by dropping the original parameter).
fToR :: Functor (Base t) => FAlgebra (Base t) a -> RAlgebra (Base t) t a
fToR f = f . fmap snd
-- | Promote an FAlgebra into a CVAlgebra (by dropping all results except the head).
fToCV :: Functor f => FAlgebra f a -> CVAlgebra f a
fToCV f = f . fmap extract
-- | Promote an RAlgebra into a CVAlgebra (by dropping all values except the most recent).
--
-- Note that this is in general O(n), since it must visit each node of the term in order to reconstruct the original term; and thus, a histomorphism performed with the resulting algebra will be O(n²).
rToCV :: (Functor (Base t), Corecursive t) => RAlgebra (Base t) t a -> CVAlgebra (Base t) a
rToCV r = r . fmap (cata (embed . tailF) &&& extract)
{-# DEPRECATED rToCV "rToCV is asymptotically inefficient. Suggest refactoring to an FAlgebra or CVAlgebra." #-}
-- | Produce a list of identifiable subterms of a given term.
--
-- By “identifiable” we mean terms which have a user-assigned identifier associated with them, & which serve as a declaration rather than a reference; i.e. the declaration of a class or method or binding of a variable are all identifiable terms, but calling a named function or referencing a parameter is not.