parsing - 调试Haskell读取函数

Question

我是 Haskell 新手，正在编写一个简单的 AI 决策系统来玩 20 个问题风格的游戏。如果程序无法猜测正确答案，它将询问一个问题来区分答案，并将该问题存储在树中。它在程序开始时从文件系统读入树，并在程序结束时将其写回。

我在 Haskell 中的序列化代码方面遇到了很多问题。我收到错误“前奏读取:未解析”。这是怎么回事？这是我的代码:

import Data.Char
import System.IO

-- Defines a type for a binary tree that holds the questions and answers
data Tree a = 
        Answer String | 
        Question String (Tree a) (Tree a)
        deriving (Read, Show)

-- Starts the game running
main = do
        let filePath = "data.txt"
        fileContents <- readFile filePath
        animals <- return (read fileContents)
        putStrLn "Think of an animal. Hit Enter when you are ready.  "
        _ <- getLine
        ask animals
        writeFile filePath (show animals)

-- Walks through the animals tree and ask the question at each node
ask :: Tree a -> IO ()
ask (Question q yes no) = do
        putStrLn q
        answer <- getLine
        if answer == "yes" then ask yes
                           else ask no
ask (Answer a) = do
        putStrLn $ "I know! Is your animal a " ++ a ++ "?"
        answer <- getLine
        if answer == "yes" then computerWins
                           else playerWins

computerWins = do putStrLn "See? Humans should work, computers should think!"

playerWins = do putStrLn "TODO"

这是我正在使用的数据文件:

Question "Does it live in the water?"
        ((Question "Does it hop?") (Answer "frog") (Answer "fish"))
        (Answer "cow")

Answer 1

read 并不是为了稳健地处理额外括号之类的事情。您的代码适用于我使用以下数据文件:

Question "Does it live in the water?"
        (Question "Does it hop?" (Answer "frog") (Answer "fish"))
        (Answer "cow")