如何更改基本情况以使其重新开始递归？

Question

我正在尝试强制递归为我的项目无限循环。 这是我到目前为止的代码：

putStr' :: String -> IO ()
putStr' (a:as) = do putChar a
                    putChar '\n'
                    threadDelay 1000000
                    putStr' as
putStr' []     = putStr'

它抛出这个错误

<interactive>:339:18: error:
    * Couldn't match expected type: IO ()
                  with actual type: String -> IO ()
    * Probable cause: putStr' is applied to too few arguments
      In the expression: putStr'
      In an equation for putStr': putStr' [] = putStr'

我也尝试过这个

putStr' :: String -> IO ()
putStr' (a:as) = do putChar a
                    putChar '\n'
                    threadDelay 1000000
                    putStr' as
putStr' []     = putStr' (a:as)

但无济于事，它告诉我：

<interactive>:297:27: error: Variable not in scope: a :: Char

<interactive>:297:29: error: Variable not in scope: as :: [Char]

我知道你不应该这样做，因为它可能很危险，但这实际上是我的代码正常工作所需要的。你能帮我吗？这可能吗？我应该尝试不同的方法，也许使用警卫或其他什么？

Answer 1

不要考虑永远循环；考虑循环一个可能是无限的列表，也可能不是无限的，然后提供一个无限列表。

putStr' :: String -> IO ()
putStr'  = traverse go . cycle  where
    go x = do putChar x
              putChar '\n'
              threadDelay 1000000