重复附加到字符串haskell

嗨，我是哈斯凯尔的新手，不知道该怎么做。到目前为止，我有以下代码

ask :: String -> IO ()
ask prompt =
  do
  putStrLn prompt
  line <- getLine
  if line == ""
    then ask "please try again"
    else putStrLn ("you said: " ++ reverse line)

main :: IO ()
main =
  do
  ask "please say something"

ask:：String->IO（）
询问提示=
做
putStrLn提示符
line您可以在方法中添加计数器，如：

ask :: String -> IO ()
ask = ask' 1

ask' :: Int -> String -> IO ()
ask' n prompt = do
  putStrLn prompt
  line <- getLine
  if null line
    then ask' (n+1) ("please try again" ++ replicate n '!')
    else putStrLn ("you said: " ++ reverse line)
ask:：String->IO（）
ask=ask'1
询问'：：Int->String->IO（）
ask'n prompt=do
putStrLn提示符
行而不是将一个提示传递给
询问
，而是以由
迭代
生成的无限列表的形式传递所有提示：

ask :: [String] -> IO ()
ask (p:ps) =
  do
  putStrLn p
  line <- getLine
  if line == ""
    then ask ps
    else putStrLn ("you said: " ++ reverse line)

main :: IO ()
main =
  do
  ask ("please say something" : iterate (++"!") "please try again")

ask:：[String]->IO（）
提问（p:ps）=
做
putStrLn p
行只是为了用另一种方法做出贡献

你想做两件事


一种是反向打印给定的字符串
另一种是处理错误，每次打印一条新的错误消息

让我们定义这两个动作：

-- This prints the given line backwards
putReverse :: String -> IO ()
putReverse line = putStrLn $ "you said: " ++ reverse line

-- Given an error message an a IO action, prints the message an execute the IO
askAgain :: String -> IO () -> IO ()
askAgain errorMessage io = putStrLn errorMessage >> io


ask
功能接收所需的错误消息作为输入。它请求一条线并处理每个案例。调用
askAgain
时，io操作与
ask
功能相同，但有新的错误信息

ask :: String -> IO ()
ask errorMessage = do
  line <- getLine
  if line == ""
    then askAgain errorMessage $ ask (errorMessage ++ "!") -- here is where you update the error message
    else putReverse line

main :: IO ()
main = do
  putStrLn "please say something" -- optionally this prompt can but an argument for ask function. Try to refactor as an exercise!!
  ask "please try again"

ask:：String->IO（）
ask errorMessage=do
线