Haskell lazy I/O and closing files

Question

I\'ve written a small Haskell program to print the MD5 checksums of all files in the current directory (searched recursively). Basically a Haskell version of md5deep

Answer 1

Edit: my assumption was that the user was opening thousands of very small files, it turns out they are very large. Laziness will be essential.

Well, you'll need to use a different IO mechanism. Either:

• Strict IO (process the files with Data.ByteString or System.IO.Strict
• or, Iteratee IO (for experts only at the moment).

I'd also strongly recommend not using 'unpack', as that destroys the benefit of using bytestrings.

For example, you can replace your lazy IO with System.IO.Strict, yielding:

import qualified System.IO.Strict as S

getList :: FilePath -> IO [String]
getList p = mapM getFileLine =<< getRecursiveContents p
    where
        getFileLine path = liftM (\c -> (hex (hash c)) ++ " " ++ path)
                                 (S.readFile path)