ch04.hs

import System.Environment (getArgs)
import Data.Char (isAsciiLower, isAsciiUpper, isDigit)
import Data.List (intercalate)

splitWith :: (a -> Bool) -> [a] -> [[a]]
splitWith pred = foldr f [[]]
    where f elem acc@(x:xs) | pred elem = (elem:x):xs
                            | otherwise = []:acc

dropOccurenses :: (Eq a) => a -> [a] -> [a]
dropOccurenses _ [] = []
dropOccurenses a (x:xs) | x == a = dropOccurenses a xs
                        | otherwise = x:dropOccurenses a xs

-- file: ch04/InteractWith.hs
-- Save this in a source file, e.g. Interact.hs



interactWith function inputFile outputFile = do
  input <- readFile inputFile
  writeFile outputFile (function input)

main = mainWith myFunction
  where mainWith function = do
          args <- getArgs
          case args of
            [input,output] -> interactWith function input output
            _ -> putStrLn "error: exactly two arguments needed"

        -- replace "id" with the name of our function below
        myFunction = transposeText


isLineSeperator x =  x == '\r' || x == '\n'
isAlphaNum x = isDigit x || isAsciiLower x || isAsciiUpper x

myLineSplitter = splitWith (not . isLineSeperator)
myWordSplitter = splitWith isAlphaNum

myFirstWordsofLines txt =
    let lines = myLineSplitter txt
        wordseparated = map myWordSplitter lines
    in show $ (dropOccurenses "" . map head) wordseparated

fixSize 0 _ = ""
fixSize n "" = replicate n ' '
fixSize n (x:xs) = x : fixSize (n-1) xs

spread :: [a] -> [[a]] -> [[a]]
spread (x:xs) (y:ys) = [y ++ [x]] : spread xs ys

transpose :: [[a]] -> [[a]]
transpose x = foldr spread (replicate (length x) []) x

transposeText txt =
    let lines = myLineSplitter txt
        maxlinesize = foldr (\l s -> max (length l) s) 0 lines
        lines' = map (fixSize maxlinesize) lines
    in intercalate "\n" $ transpose lines'