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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 #-} {-# LANGUAGE DataKinds, GeneralizedNewtypeDeriving, TemplateHaskell, TypeOperators #-}
module Language.Ruby.Syntax where module Language.Ruby.Syntax where
import Data.Functor.Foldable (Base, Corecursive(..)) import Data.Functor.Foldable (Base)
import Data.Functor.Union import Data.Functor.Union
import Data.Record import Data.Record
import qualified Data.Syntax as Syntax 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'. -- | An R-algebra on some carrier functor 'f' of its fixpoint type 't'.
type RAlgebra f t a = f (t, a) -> a 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). -- | 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 :: Functor (Base t) => FAlgebra (Base t) a -> RAlgebra (Base t) t a
fToR f = f . fmap snd 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. -- | 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. -- 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.