如何利用Redis和Haskell开发限流器功能

import qualified Database.Redis as R
import Control.Monad.Trans (liftio)
import Control.Concurrent (threadDelay)

-- 连接Redis数据库
connectRedis :: IO R.Connection
connectRedis = R.checkedConnect R.defaultConnectInfo

-- 增加计数器的值
incrCounter :: R.Connection -> String -> IO Integer
incrCounter conn key = liftIO $ R.incr conn key

-- 获取计数器的值
getCounter :: R.Connection -> String -> IO Integer
getCounter conn key = liftIO $ do
   counter <- R.get conn key
   case counter of
     Right (Just val) -> return $ read val
     _ -> return 0

-- 限制处理函数
limitHandler :: R.Connection -> Integer -> Integer -> IO ()
limitHandler conn limit interval = do
   counter <- getCounter conn "requestCounter"
   putStrLn $ "Counter: " ++ show counter
   if counter >= limit
     then putStrLn "Request limit exceeded"
     else do
       _ <- incrCounter conn "requestCounter"
       -- 执行请求的代码
       putStrLn "Processing request"
       -- 模拟延时处理
       liftIO $ threadDelay 1000000
       _ <- R.decr conn "requestCounter"
       putStrLn "Request processed"

-- 主函数
main :: IO ()
main = do
   conn <- connectRedis
   -- 初始化计数器
   _ <- R.set conn "requestCounter" "0"
   -- 执行限流处理
   limitHandler conn 3 10