Lazy Pirate client in Haskell

{--
Lazy Pirate client in Haskell
--}
module Main where

import System.ZMQ4.Monadic
import System.Random (randomRIO)
import System.Exit (exitSuccess)
import Control.Monad (forever, when)
import Control.Concurrent (threadDelay)
import Data.ByteString.Char8 (pack, unpack)

requestRetries = 3
requestTimeout_ms = 2500
serverEndpoint = "tcp://localhost:5555"

main :: IO ()
main =
runZMQ $ do
liftIO $ putStrLn "I: Connecting to server"
client <- socket Req
connect client serverEndpoint

sendServer 1 requestRetries client

sendServer :: Int -> Int -> Socket z Req -> ZMQ z ()
sendServer _ 0 _ = return ()
sendServer seq retries client = do
send client [] (pack $ show seq)

pollServer seq retries client

pollServer :: Int -> Int -> Socket z Req -> ZMQ z ()
pollServer seq retries client = do
[evts] <- poll requestTimeout_ms [Sock client [In] Nothing]

if In ‘elem` evts
then do
reply <- receive client
if (read . unpack $ reply) == seq
then do
liftIO $ putStrLn $ "I: Server replied OK " ++ (unpack reply)
sendServer (seq+1) requestRetries client
else do
liftIO $ putStrLn $ "E: malformed reply from server: " ++ (unpack reply)
pollServer seq retries client
else
if retries == 0
then liftIO $ putStrLn "E: Server seems to be offline, abandoning" >> exitSuccess
else do
liftIO $ putStrLn $ "W: No response from server, retrying…"
client’ <- socket Req
connect client' serverEndpoint
send client' [] (pack $ show seq)
pollServer seq (retries-1) client'