Take a string and split it over multiple lines of a specified max length. If a word is too big to fit on a single line, just put it on its own line for simplicity.

makeLines.hs

import Data.List

makeLines :: Int -> String -> String
makeLines len = (intercalate "\n") . (foldl (buildLine len) [""]) . words
  where
    buildLine :: Int -> [String] -> String -> [String]
    buildLine len currLines word =
      if length newLine > len
        then currLines ++ [word]
        else ls ++ [newLine]
      where
        ls = init currLines
        l = last currLines
        newLine = dropWhile (==' ') $ l ++ " " ++ word