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Define synonyms for open-recursive F- and R-algebras.

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Rob Rix 2017-11-24 13:58:46 -05:00
parent b70e5ead7e
commit 58dc2d7b75
1 changed files with 9 additions and 1 deletions
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src/Decorator.hs
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@ -1,7 +1,9 @@
{-# LANGUAGE DataKinds, GADTs, GeneralizedNewtypeDeriving, MultiParamTypeClasses, ScopedTypeVariables, TypeFamilies, TypeOperators, UndecidableInstances #-}
{-# LANGUAGE DataKinds, GADTs, GeneralizedNewtypeDeriving, MultiParamTypeClasses, RankNTypes, ScopedTypeVariables, TypeFamilies, TypeOperators, UndecidableInstances #-}
module Decorator
( FAlgebra
, RAlgebra
, OpenFAlgebra
, OpenRAlgebra
, fToR
, decoratorWithAlgebra
, identifierAlgebra
@ -37,6 +39,12 @@ type FAlgebra t a = Base t a -> a
-- | An R-algebra on some 'Recursive' type @t@.
type RAlgebra t a = Base t (t, a) -> a
-- | An open-recursive F-algebra on some 'Recursive' type @t@.
type OpenFAlgebra t a = forall b . (b -> a) -> Base t b -> a
-- | An open-recursive R-algebra on some 'Recursive' type @t@.
type OpenRAlgebra t a = forall b . (b -> (t, a)) -> Base t b -> a
-- | Promote an FAlgebra into an RAlgebra (by dropping the original parameter).
fToR :: Functor (Base t) => FAlgebra t a -> RAlgebra t a
fToR f = f . fmap snd