Using MySQL with Wai and Warp

Question

I was wondering if below is the correct convention for combining Wai with a Database pool.

What I basically do is, create a pool, partially apply a function of type Pool -> Application and use it to pass it to Warp's run. Does it look ok, or shall I refactor it?

{-# LANGUAGE OverloadedStrings #-}
import Network.Wai
import Network.HTTP.Types
import Network.Wai.Handler.Warp (run)
import Database.MySQL.Simple
import Data.Pool (Pool, createPool, withResource)
newConn = connect defaultConnectInfo 
 { connectHost = "db"
 , connectUser = "root"
 , connectPassword = "secret"
 , connectDatabase = "test" }
getPool = createPool newConn close 1 10 5
app :: Pool Connection -> Application
app pool _ respond = do
 withResource pool $ \c -> query_ c "SELECT 1" :: IO [Only Int]
 respond $ responseLBS
 status200
 [("Content-Type", "text/plain")]
 "Hello, Web!"
main :: IO ()
main = do
 putStrLn $ "http://localhost:8080/"
 pool <- getPool
 run 8080 $ app $ pool

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Answer 1

I'm afraid there isn't much to remove. The $ after putStrLn and between app and pool are superfluous. You could write the last two lines run 8080 . app <$> getPool. I'd inline getPool. You may be interested in https://github.com/alevy/simple/blob/master/simple/src/Web/Simple.hs#L134 for boilerplate reduction.