linebreak.hs

-- code from https://www.infoq.com/presentations/Type-Functional-Design with bug related to 
-- assumption of trailing spaces after words

import Data.List;

lineBreak :: String -> String
lineBreak = joinedLines . wordJoinedLines . 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) . scanl1 (+) . map wordLength

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

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

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