rio.hs

#!/usr/bin/env stack
{- stack --install-ghc
    --resolver lts-10.8
    script
    --compile
    --package monad-logger
    --package katip
    --package universum
    --package lens
-}

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE FlexibleContexts #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE NoImplicitPrelude #-}
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE UndecidableInstances #-}
{-# LANGUAGE TemplateHaskell #-}

import Universum
import Control.Lens.TH

main = pure ()

newtype RIO r a = RIO { runRIO :: ReaderT r IO a} deriving (Functor, Applicative, Monad, MonadReader r)

data Logging r = Logging
  { _log :: Text -> RIO r ()
  }

data App = App
  { _appLogImpl :: Logging App
  }

makeLenses ''App

-- TH
instance HasLoggingImpl App where
  logImpl = appLogImpl

class HasLoggingImpl r where
  logImpl :: Lens' r (Logging r)

log :: HasLoggingImpl r => Text -> RIO r ()
log t = do
  impl <- fmap (view logImpl) ask
  _log impl t