Haskell中的字数统计实用程序[关闭]

Question

我对 Haskell 还很陌生。几天来，我一直在尝试创建一个实用程序来计算 Haskell 中的单词和行数，以帮助我更好地理解该语言。但是，我正在努力让它发挥作用。

到目前为止，我有：

wordCountUtility = do

       putStrLn "Please enter the filename:"

       filename <- getLine

       putStrLn ("The file name you have entered is: " ++ filename)

      contents <- readFile filename -- read the file specified in “name” into “contents”

      lower <- (return . map toLower) contents

      putStrLn lower

我尝试使用 'chop' 并找到 print . length . words =<< getContents 并对其进行了多次修改，但我没有运气。 我也在 Stack Overflow 上看过不少类似的答案，例如：identifying number of words in a paragraph using haskell

输出应该有点类似这样：

Amount of Lines within the file
Lines : 10

Amount of Words found within the file
Words : 110

任何帮助将不胜感激。

Answer 1

您的wordCountUtility 可能还没有计算字数。你应该停在像

commandLineUtility :: (String -> String) -> IO ()
commandLineUtility fn = do
       putStrLn "Please enter the filename:"
       filename <- getLine
       putStrLn ("The file name you have entered is: " ++ filename)
       contents <- readFile filename -- read the file specified in “name” into “contents”
       lower <- (return . fn) contents
       putStrLn lower 

（我尽可能地贴近你的文字。）但是，现在，你必须弄清楚什么 (String -> String) 要应用的函数。这是一个纯函数，应该单独开发。所以你可以写：

cwlcount :: String -> (Int, Int, Int)
cwlcount str = (length str, length (words str), length (lines str))

format :: (Int, Int, Int) -> String
format (c,w,l) = unlines $
     ["Number of characters:"
     , show c
     , "Number of words:"
     , show w
     , "Number of lines:"
     , show l
     ]

所以(format . cwlcount) :: String -> String，你可以写：

 main :: IO ()
 main = commandLineUtility (format . cwlcount)

当然，对这个程序有上百万的反对意见，但您可以通过逐个调查部分来改进它。一方面，将整个字符列表带入内存并分别对其进行三个长度计算是令人恼火的。 Predude.getLine 也不是很友好......

那么，目前我们的结果是这样的：

$ ghci Sonia_CS.hs 
GHCi, version 7.8.3: http://www.haskell.org/ghc/  :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer-gmp ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main             ( Sonia_CS.hs, interpreted )
Ok, modules loaded: Main.
>>> main
Please enter the filename:
Sonia_CS.hs
The file name you have entered is: Sonia_CS.hs
Number of characters:
816
Number of words:
110
Number of lines:
25

或者更好：

$ ghc -O2 Sonia_CS.hs 
[1 of 1] Compiling Main             ( Sonia_CS.hs, Sonia_CS.o )
Linking Sonia_CS ...
$ ./Sonia_CS 
Please enter the filename:
/usr/share/dict/words
The file name you have entered is: /usr/share/dict/words
Number of characters:
2493109
Number of words:
235886
Number of lines:
235886