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Created October 20, 2020 04:20
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freereader.hs
{-# Language DeriveFunctor #-}
module Help where
import Control.Monad.Free
newtype ReaderF r a = Ask (r -> a)
deriving Functor
type Reader r = Free (ReaderF r)
runReaderF :: r -> ReaderF r a -> a
runReaderF r (Ask f) = f r
runReader :: r -> Reader r a -> a
runReader r = iter (runReaderF r)
ask :: Reader r r
ask = wrap (Ask pure)
local :: (r -> s) -> Reader s a -> Reader r a
local f = hoistFree (\(Ask g) -> Ask (g . f))
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