Lazy ByteString奇怪的行爲或錯誤？

Question

當我在GHCI測試我的功能intervalFinder它似乎是工作，但是當我嘗試編譯它，我沒有輸出：

該功能適用​​於輸入：

*Main> intervalFinder $[B.pack"first",B.pack"second",B.empty,B.pack"third",B.emp 
ty] 
Loading package bytestring-0.9.2.1 ... linking ... done. 
["Start Time: first","End Time: second","Start Time: third","End Time: third 
"] 

而且在RESULTS.TXT

*Main> main 
Loading package bytestring-0.9.2.1 ... linking ... done. 
*Main> :q 
Leaving GHCi. 

打印：運行主

Start Time: firstEnd Time: secondStart Time: thirdEnd Time: third 

但如果我運行ghc test3.hs，輸出文件是0kb（並且顯然沒有數據！）

我做錯了什麼？

代碼：

{-# LANGUAGE OverloadedStrings #-} 
import qualified Data.ByteString.Char8 as B 
import qualified Data.ByteString.Lazy.Char8 as Bl 
import System.IO 
import System.Environment 


intervalFinder :: [B.ByteString]->[B.ByteString] 
intervalFinder x = helper x "" 
    where 
    helper (x:xs) "" 
     | x /= "" = ((B.append (B.pack("Start Time: ")) x)):(helper xs x) 
     | otherwise = helper xs "" 
    helper (x:xs) y 
     | x == "" = ((B.append (B.pack("End Time: ")) y)):(helper xs "") 
     | otherwise = helper xs x 
    helper _ _  = [] 

main = do 
    filehandle <- openFile "result.txt" WriteMode 
    Bl.hPutStr (filehandle) . Bl.fromChunks . intervalFinder $[B.pack"first",B.pack"second",B.empty,B.pack"third",B.empty] 

謝謝！

Answer 1

main = do 
    filehandle <- openFile "result.txt" WriteMode 
    Bl.hPutStr (filehandle) . Bl.fromChunks . intervalFinder 
      $[B.pack"first",B.pack"second",B.empty,B.pack"third",B.empty] 

的輸出進行緩衝，所以程序退出而不與runghc或編譯的二進制沖洗緩衝液中。在ghci中，當ghci退出1時，所有緩衝區都將被刷新。

當你openFile一個文件句柄，你應該使用它hClose它。如果在寫或附加模式下打開輸出緩衝區，也會刷新輸出緩衝區。

main = do 
    filehandle <- openFile "result.txt" WriteMode 
    Bl.hPutStr (filehandle) . Bl.fromChunks . intervalFinder 
      $[B.pack"first",B.pack"second",B.empty,B.pack"third",B.empty] 
    hClose filehandle 

或者，你可以使用writeFile

main = Bl.writeFile "result.txt" $ Bl.fromChunks ... 

¹我不知道的是100％，但經驗支持它。