foo.hs

app :: Logger -> OSEnv -> Application
app l e = serve api (hoistServer api (toHandler l e) server)

toHandler :: Logger -> OSEnv -> AppM a -> Handler a
toHandler logger env = coerce . mkHandler . catchRemEx
  where
    mkHandler :: AppM a -> IO a
    mkHandler h = flip runLoggingT logger $
          runReaderT h env

startServer :: OSEnv -> RunFlags -> IOL ()
startServer env rf = do
    logger <- askLoggerIO
    liftIO $ withStdoutLogger $ \ap -> do
        let app' :: Application
            app' = logMiddleware ap (app logger env)
        runSettings settings app'