Effectful.Provider

>>> import Control.Monad.IO.Class>>> import Data.Map.Strict qualified as M>>> import Effectful.Dispatch.Dynamic>>> import Effectful.State.Static.Local

>>> :{  data Write :: Effect where    Write :: String -> Write m ()  type instance DispatchOf Write = Dynamic:}

>>> :{  write :: Write :> es => String -> Eff es ()  write = send . Write:}

>>> :{  action :: Provider_ Write FilePath :> es => Eff es ()  action = do    provideWith_ @Write "in.txt" $ do      write "hi"      write "there"    provideWith_ @Write "out.txt" $ do      write "good"      write "bye":}

>>> :{  runWriteIO    :: IOE :> es    => FilePath    -> Eff (Write : es) a    -> Eff es a  runWriteIO fp = interpret_ $ \case    Write msg -> liftIO . putStrLn $ fp ++ ": " ++ msg:}

>>> :{  runWritePure    :: State (M.Map FilePath [String]) :> es    => FilePath    -> Eff (Write : es) a    -> Eff es a  runWritePure fp = interpret_ $ \case    Write msg -> modify $ M.insertWith (++) fp [msg]:}

>>> :{  runEff    . runProvider_ runWriteIO    $ action:}in.txt: hiin.txt: thereout.txt: goodout.txt: bye

>>> :{  runPureEff    . fmap (fmap reverse)    . execState @(M.Map FilePath [String]) M.empty    . runProvider_ runWritePure    $ action:}fromList [("in.txt",["hi","there"]),("out.txt",["good","bye"])]

>>> :{  adjustPaths    :: Provider_ Write FilePath :> es    => Eff es a    -> Eff es a  adjustPaths = interpose @(Provider_ Write FilePath) $ \env -> \case    ProvideWith fp action -> do      passthrough env $ ProvideWith ("logs/" ++ fp) action:}

>>> :{  runEff    . runProvider_ runWriteIO    . adjustPaths    $ action:}logs/in.txt: hilogs/in.txt: therelogs/out.txt: goodlogs/out.txt: bye