如何在Haskell中打印出二進制文件中的字節？

Question

我的打印語句一直拋出錯誤，不太明白髮生了什麼。

import Data.ByteString.Lazy as BS 
import Data.Word 
import Data.Bits 

readByte :: String -> IO [Word8] 
readByte fp = do 
    contents <- BS.readFile fp 
    return $ Prelude.take 5 $ unpack contents 

main :: IO() 
main = do 
    input <- readByte "DATA.BIN" 
    print "Byte 0: " ++ [input!!0] 

獲取以下錯誤：

Couldn't match expected type `[()]' with actual type `IO()' 
In the return type of a call of `print' 
In the first argument of `(++)', namely `print "Byte 0: "' 

Answer 1

Haskell是解析print "Byte 0: " ++ [input!!0]爲(print "Byte 0: ") ++ [input!!0]，這可能不是你的原意。你可能想

main :: IO() 
main = do 
    input <- readByte "DATA.BIN" 
    putStrLn $ "Byte 0: " ++ show (input!!0) 

代替