import Prelude hiding (all, concatMap, unlines)

copyFile :: FilePath -> FilePath -> IO ()
copyFile from to = readFile from >>= writeFile to

fileLength :: FilePath -> IO Int
fileLength fn = readFile fn >>= return . length

-- Returns the number of lines in a file.
numOfLines :: FilePath -> IO Int
numOfLines fn = readFile fn >>= return . length . lines
  
-- Returns the number of empty/blank lines in a file.
numberOfBlankLInes :: FilePath -> IO Int
numberOfBlankLInes fn =
  readFile fn >>= return . length . filter (all (==' ')) . lines
     
allBlanks :: String -> Bool
allBlanks s = foldr (&&) True (map (==' ') s)

-- Returns True if all elements of a list satisfy the given predicate.
all :: (a -> Bool) -> [a] -> Bool
--all p xs = foldr (&&) True (map p xs)
all p = foldr (&&) True . map p

enumerateLines :: String -> String
enumerateLines = unlines
                 . map (uncurry (++))
                 . zip (map (\n -> show n ++ ": ") [1..])
                 . lines

concatMap :: (a -> [b]) -> [a] -> [b]
concatMap f = concat . map f

unlines :: [String] -> String
unlines = concatMap (++"\n")

showEnumeratedFileLines :: String -> IO ()
showEnumeratedFileLines fn = readFile fn >>= putStr . enumerateLines