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PODebugging Haskell read function
 

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    <p>I'm new to Haskell and I'm writing a simple AI decision system to play a 20 questions style of game. If the program is unable to guess the correct answer, it will ask for a question to use to distinguish the answer and it will store that question in a tree. It reads the tree in from the file system at the start of the program and writes it back out at the end.</p> <p>I'm having a lot of problems with the serialization code in Haskell. I'm getting the error "Prelude read: no parse". What's going on? Here's my code:</p> <pre><code>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 &lt;- readFile filePath animals &lt;- return (read fileContents) putStrLn "Think of an animal. Hit Enter when you are ready. " _ &lt;- getLine ask animals writeFile filePath (show animals) -- Walks through the animals tree and ask the question at each node ask :: Tree a -&gt; IO () ask (Question q yes no) = do putStrLn q answer &lt;- getLine if answer == "yes" then ask yes else ask no ask (Answer a) = do putStrLn $ "I know! Is your animal a " ++ a ++ "?" answer &lt;- getLine if answer == "yes" then computerWins else playerWins computerWins = do putStrLn "See? Humans should work, computers should think!" playerWins = do putStrLn "TODO" </code></pre> <p>And here's the data file I'm using:</p> <pre><code>Question "Does it live in the water?" ((Question "Does it hop?") (Answer "frog") (Answer "fish")) (Answer "cow") </code></pre>
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    1. CO`Tree` doesn't need a type qualifier - you can easily replace all `Tree a` with `Tree`, without changing your program behavior.
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