Question

我有编写Quiz Animal游戏的任务。我必须从文件中读取树数据（文件的结构是免费的）。游戏结束后可以在树中添加新数据（实际上（动物）将被替换为（Node（Animal）（Animal））。

我的问题是我无法解析AnimalsTree中的“database.txt”内容

示例“database.txt”（此内容是在调用“新游戏”之前通过写入生成的）：

问题“飞吗？” （动物“鸟”）（问题“游泳吗？”（动物“鱼”）（动物“狗”））

修改这是完整的代码：

module Main where
import System.IO
data AnimalsTree = Animal String | Question String AnimalsTree AnimalsTree deriving (Read, Show)
-- Видовете отговори на потребителя
data Answer = Yes | No

main :: IO ()
main = do root <- "database.txt"
          play (read root)
          return ()

play :: AnimalsTree -> IO AnimalsTree
play root = do putStrLn "Think of an animal, I will try to guess what it is..."
               newRoot <- play' root
               writeFile "database.txt" (show newRoot)
               playAgain <- ask "Do you want to play again?"
               case playAgain of
                   Yes -> play newRoot
                   No  -> do putStrLn "Bye!"
                             return newRoot

play' :: AnimalsTree -> IO AnimalsTree
play' question@(Question q l r) = do ans <- ask q
                                     case ans of
                                        Yes -> do y <- play' l
                                                  return $ Question q y r
                                        No  -> do n <- play' r
                                                  return $ Question q l n

play' animal@(Animal _) = do ans <- ask $ "Are you thinking of " ++ show' animal ++ "?"
                             case ans of
                                Yes -> do putStrLn "I win! :)"
                                          return animal
                                No  -> do putStrLn "I give up, you win!"
                                          getNewAnimal animal


getNewAnimal :: AnimalsTree -> IO AnimalsTree
getNewAnimal animal = do putStrLn "Please help me!"
                         putStrLn "What is name of yout animal?"
                         name <- getLine
                         let newAnimal = Animal name
                         putStrLn $ "Now please enter a question that answers yes for " ++ show' newAnimal ++ " and no for " ++ show' animal
                         question <- getLine
                         return $ Question question newAnimal animal

ask :: String -> IO Answer
ask s = do putStrLn $ s ++ " (Yes/No)"
           getAnswer

getAnswer :: IO Answer
getAnswer = do ans <- getLine
               putStrLn ""
               case ans of
                   "y" -> return Yes
                   "Y" -> return Yes
                   "yes" -> return Yes
                   "Yes" -> return Yes
                   "n" -> return No
                   "N" -> return No
                   "no" -> return No
                   "No" -> return No
                   _   -> putStrLn "This is incorect answer! Please try again with value in 'Yes' or 'No'!" >> getAnswer

show' (Animal name) = (if elem (head name) "AEIOUaeiou" then "an " else "a ") ++ name
show' (Question q _ _) = q

但我得到以下错误：

test3.hs:10:19:
    No instance for (Read (IO AnimalsTree))
      arising from a use of ‘read’
    In a stmt of a 'do' block: root <- read "database.txt"
    In the expression:
      do { root <- read "database.txt";
           play (root);
           return () }
    In an equation for ‘main’:
        main
          = do { root <- read "database.txt";
                 play (root);
                 return () }

Answer 1

这看起来是一个很好的开始！我只需要将readFile添加到您的main函数中以使其编译：

main = do root <- readFile "database.txt"

您可能需要从readFile切换到显式打开文件以进行读取，读取和关闭文件。这是因为readFile无法保证何时关闭文件，如果为writeFile提供了已经打开的文件的路径，则允许openFile失败。

您可以阅读hGetLine，hClose和hGetContents的文档，了解有关如何执行此操作的详细信息（但请注意readFile，因为它有相同的注意事项{{1}}确实如此。

从Haskell中的文件解析二叉树

1 个答案: