Add a simple logging effect and adapt only at IO sites

src/Main.hs

@@ -13,6 +13,9 @@ import Network.Wai.Handler.Warp (run)
 import Servant hiding           ((:>), throwError)
 import qualified Servant        as S
 
+--
+-- Application
+--
 main :: IO ()
 main = run port $ serve proxy app
 
@@ -23,8 +26,14 @@ app = α $ rootHandler
      :<|> userPostHandler
 
 α :: ServerT API AppEff -> ServerT API Handler
-α = hoistServer proxy $ Handler . ExceptT .
-  runEff . runErrorNoCallStack . runFileSystem . runDatabaseIO
+α = hoistServer proxy 
+  $ Handler 
+  . ExceptT 
+  . runEff 
+  . runErrorNoCallStack
+  . runLoggerIO
+  . runFileSystem
+  . runDatabaseIO
 
 port :: Int
 port = 8080