Haskell Reading lines from File and print these with modifications

Question

i want to read a file containing one word per line and print this file line by line, adding the length of the word at the end of the line.

So far i got to this solution and it drops errors with mismatching types.

I've tried this for several days now and I lost all faith. I am unable to wrap my head around Haskell.

I hope someone can help me.

Here is my code:

import System.IO


main :: IO ()
main = do

  file <- readFile "palindrom.txt"
  putStrLn (unlines $ showLength $ lines file)

showLength (x:xs) = (x concat "has length of" length x) (showLength xs)

Answer 1

Change it to

showLength :: [[Char]] -> [[Char]]
showLength (x:xs) = -- (x concat "has length of" length x) (showLength xs)
            concat [x, " has length of ", show (length x)] : showLength xs
showLength  []  =  []

and it will work. Your original code here does not make much sense in Haskell.

concat :: [[a]] -> [a] is a built-in function which concatenates together all the lists in a given list:

> concat [[1],[2,3],[4]]
[1,2,3,4]

> concat ["a"," b ", "123"]
"a b 123"