Haskell逐行打印文件

Question

EDIT: New code added and new errors changed too. It compiles!

I am a newbie to Haskell, and am running into a problem in a code I'm trying to create for printing lines from a text file. In doing this, I would need the output of the file to list the lines one by one and number them, and put a row of dashes between lines that don't start with the same character. Here is an example of the output I want:

$runghc group.hs (file I input)
1 able
2 academia
3 algae
------
4 carton
------
5 fairway
------
6 hex
7 hockshop

And here is the code that I have currently. I think I'm approaching this from the right direction, but I am running into some errors.

import System.Environment (getArgs)

group :: [Char] -> [Char]
group file = printSplit (words (show file)) 1

printSplit (x:[]) n = show n ++ x 
printSplit (x:t) n
       | head x == head (head t) = ((show n) ++ x) ++ printSplit t (n+1)
       | otherwise = ((show n) ++ x ++ "\n------") ++ printSplit t (n+1)

main = do
 args <- getArgs
 bytes <- readFile (head args)
 putStrLn (group bytes)

I am running into this error:

*Main> main
1"able\nacademia\nalgae\ncarton\nfairway\nhex\nhockshop\n"

And don't quite yet know how to do with this...

---

ORIGINAL POST INFO: A different way I'm attempting is to do words (show file) which will give me

["able","academia","algae","carton","fairway","hex","hockshop"]

But I'm not sure where to go after that. And since I'm trying to learn higher-order functions, maybe someone could explain how to use map or fold to try these to me if possible? :)

Answer 1

Since you're using n in a concatenation, GHC assumes that n is a [Char] . However, you want n to be an Int or something similar and use show n whenever you want to transform it to a String .

The other error has to do with the return of group . Since group is just printSplit with some fixed parameters, it has the same return type, which is [String] or [[Char]] . However, putStrLn expects a single String. You can use unlines or concat in order to concatenate your strings.