rename files in git lost-found directory - v2

rename-lost-files-2.hs

-- rename Project Euler files in git lost-found directory

-- get the file type and the problem number from the initial comments
-- in each file

import System.Directory
import Text.Regex.Posix
import Control.Monad (forM_)

lostFilesDir = ".git/lost-found/other"

fileType s =
  let firstToken = head $ fst $ head $ lex s
  in case firstToken of
    ';' -> "clj"
    '-' -> "hs"
    '#' -> "pl"
    _   -> "??"

problemId contents =
  safeHead $ map snd $ problemIds $ pairwise $ words contents
  where pairwise ws = zip ws $ tail ws
        problemIds = filter (\(a, b) -> a `elem` ["Problem", "problem"])
        safeHead [] = Nothing
        safeHead (x:_) = Just x

findFileName contents =
  fmap (\x -> ft ++ "/" ++ x ++ "." ++ ft) prid
  where ft   = fileType contents
        prid = problemId contents

inferFileName path = do
  contents <- readFile path
  return $ findFileName contents

main = do
  dirContents <- getDirectoryContents lostFilesDir
  let lfiles = filter (\file -> not $ file `elem` [".", ".."]) dirContents
  forM_ lfiles (\lfile -> do
                   fname <- inferFileName $ lostFilesDir ++ "/" ++ lfile
                   putStrLn $
                     case fname of
                       Just x -> lfile ++ " -> " ++ x
                       _      -> lfile ++ ": No program??"
                )