[Haskell] Reading a directory tree

[Glynn Clements]

Tom Hofte wrote:

> I'm looking for a way to iteratively read all the files in a directory
> and
> its subdirectories, given the filepath of the top-level dir.
> For example, I want to find a file, corresponding to a given filename,
> in a directory and its subdirectories.
> 
> Is there a way to implement this in Haskell?

This is somewhat simpler than the other examples which have been
given.

> import Monad
> import Directory
> 
> scanDir :: FilePath -> IO [FilePath]
> scanDir dir = do
> 	names <- getDirectoryContents dir
> 	let names' = filter ((/= '.') . head) names
> 	let paths = map ((dir ++ "/") ++) names'
> 	dirs <- filterM doesDirectoryExist paths
> 	files <- filterM doesFileExist paths
> 	rest <- mapM scanDir dirs
> 	return $ files ++ concat rest

One caveat: (scanDir "/") isn't handled correctly; you will get an
extra slash, i.e. "//usr", "//bin" etc. Not that I'd recommend using
this code for scanning an entire filesystem, due to performance
issues.

-- 
Glynn Clements <glynn.clements at virgin.net>