import Prelude hiding (concatMap, unlines)

-- Prefix all lines in a given string with the corresponding line number:
enumerateLines :: String -> String
enumerateLines = unlines . map (uncurry (++))
                         . zip (map (\s -> show s ++ ": ") [1..])
                         . lines

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

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

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