Better

gistfile1.hs

import Data.List

lineBreak :: String -> String
lineBreak = joinBrokenLines . joinWordsInBrokenLines . brokenLines . words

brokenLines :: [String] -> [[String]]
brokenLines [] = []
brokenLines wordList = brokenLine : brokenLines remainingWords
  where (brokenLine, remainingWords) = splitAt (brokenLineWordCount wordList) wordList

brokenLineWordCount :: [String] -> Int
brokenLineWordCount = length . takeWhile (<= 13) . scanl (+) 0 . map wordLength

wordLength :: String -> Int
wordLength = succ . length

joinWordsInBrokenLines :: [[String]] -> [String]
joinWordsInBrokenLines = map (intercalate " ")

joinBrokenLines :: [String] -> String
joinBrokenLines = intercalate "\n"