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as-capabl/upgrade.hs

Created August 25, 2017 08:58
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extensible-effectsの作用の拡大
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upgrade.hs
{-# LANGUAGE TypeOperators #-}
{-# LANGUAGE TypeFamilies #-}
import Control.Eff
import Control.Monad.Free.Reflection
import Data.OpenUnion
import Data.Typeable
-- http://aiya000.github.io/posts/2017-08-22-my-experience-of-eff-convertion.html
upgrade :: (Functor t, Typeable t) => Eff r a -> Eff (t :> r) a
upgrade = fromView . go . toView
where
go (Impure uni) = Impure $ weaken (upgrade <$> uni)
go (Pure x) = Pure x
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