src/Effectful/Reader.hs · effectful

git.iko.soy/effectful

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1-- | The 'Reader' effect.

2module Effectful.Reader

3 ( Reader

4 , runReader

5 , ask

6 , asks

7 , local

8 ) where

10import Effectful.Internal.Effect

11import Effectful.Internal.Monad

13-- | Provide access to a strict (WHNF), thread local, read only value of type

14-- @r@.

15newtype Reader r :: Effect where

16 Reader :: r -> Reader r m a

18runReader :: r -> Eff (Reader r : es) a -> Eff es a

19runReader r = evalEffect (IdE (Reader r))

21ask :: Reader r :> es => Eff es r

22ask = do

23 IdE (Reader r) <- getEffect

24 pure r

26asks :: Reader r :> es => (r -> a) -> Eff es a

27asks f = do

28 IdE (Reader r) <- getEffect

29 pure $ f r

31local :: Reader r :> es => (r -> r) -> Eff es a -> Eff es a

32local f = localEffect $ \(IdE (Reader r)) -> IdE (Reader (f r))