proposal to add filesWithExtension

[juhp]

I would like to suggest adding a couple of small functions to System.Directory.Extra:

filesWithExtension :: FilePath -- directory
                   -> String   -- file extension
                   -> IO [FilePath]

fileWithExtension :: FilePath -- directory
                  -> String   -- file extension
                  -> IO (Maybe FilePath)

How does that sound? If it is okay I am happy to open a PR for it.

[ndmitchell]

The second one seems redundant - it's easier to do listToMaybe over the first, or whatever is the right policy to reduce many files down to one.

For filesWithExtension, what's the benefit over just doing the listFiles and a filter? My concern is you often want to list files directly, with recursion, and with recursion avoiding . prefixed directories or similar. By the time you have three variants it starts to explode badly in terms of complexity.

[juhp]

This an implementation of filesWithExtension:

filesWithExtension :: FilePath -> String -> IO [FilePath]
filesWithExtension dir ext =
  filter (ext `isExtensionOf`) <$> listFiles dir

I admit it looks pretty straightforward (specially when one remembers to use isExtensionOf). Maybe listFilesWithExtension would be a better name.

I see your point, though I find myself using filesWithExtension (and less often fileWithExtension) in various projects: it is a bit less typing. :-)

[ndmitchell]

Yeah, I think I'll close this for now, and not add it. But if in 6 months time or so you've needed to use that one a lot, but not any of the other variations with isExtensionOf, it might be worth considering.