[mifrai]

Honestly, I don't think danidiaz was trying to be clever so much as not knowing about the existence of filterM. A good chunk of the code was just an implementation of it:

    filterM' f xs = map fst . filter snd . zip xs <$> mapM f xs

So, given filterM, the code would have looked like

    nexist n xs = take n <$> filterM (fmap not . doesFileExist) xs

Which doesn't look clever at all and it's fairly easy to understand.

[danidiaz]

Yeah, I had forgotten about filterM.

By the way, I like the (fmap not . doesFileExist) bit. It´s cleaner and less cluttered than (\f -> doesFileExist f >>= return . not)

[Maro]

Cool, thanks!