无法匹配 haskell 中的预期类型错误

Question

我\xc2\xb4m试图实现一个通过txt文件保存游戏中玩家最高分的功能。这是代码：

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import System.IO\nimport System.Directory\n\nsaveHighScore:: Int -> IO()\nsaveHighScore num = do\n  let stringNum = "" ++ show num\n  let file = "score.txt"\n  writeFile file stringNum\n\nreadHighScore:: IO() -> Int\nreadHighScore = do \n  content <- openFile "score.txt" ReadMode\n  score <- hGetContents content\n  let highScore = read score :: Int\n  return highScore\n

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但代码给出了这个错误，我不知道该怎么做：

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localStorage.hs:17:9: error:\n* Couldn't match expected type: IO () -> Int\n              with actual type: IO Int\n* In a stmt of a 'do' block:\n    content <- openFile "score.txt" ReadMode\n  In the expression:\n    do content <- openFile "score.txt" ReadMode\n       score <- hGetContents content\n       let highScore = ...\n       return highScore\n  In an equation for `readHighScore':\n      readHighScore\n        = do content <- openFile "score.txt" ReadMode\n             score <- hGetContents content\n             let highScore = ...\n             ....\n |\n17|         content <- openFile "score.txt" ReadMode\n |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^\n

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Answer 1

错误消息准确地告诉您出了什么问题。您声称您的函数具有 type IO () -> Int，但任何有趣的函数都不可能具有这种类型。唯一可能的实现是一个常量函数，它忽略IO ()并产生相同的结果，无论其输入如何。

正确的类型是编译器建议的类型，IO Int.