[Haskell-cafe] Suggested additions to System.FilePath.Posix/Windows

17 Sep 2009

      Hello Neil

I used System.FilePath.Posix quite extensively recently, and I thank
you for the package filepath.  There were however two words that I
needed which I could not construct from those in
System.FilePath.Posix.  They are maybe of interest to you and others.

I submit these two words to you for consideration for inclusion in
System.FilePath.Posix.  Please change the names as you see fit.

I do not know if they make sense for System.FilePath.Windows.  If
the do not make sense, then please feel free to drop them so as to
preserve the interface.

As requested, I Cc'ed the haskell-cafe, but I am not at the moment
following these threads, so if anyone else responds, please Cc me
if you wish.

Thanks again and cheers,
- Marcus

P.S. Here they are.  Although I use ksh(1) as an example, this is a
feature of POSIX shells.
...
-- | 'reduceFilePath' returns a pathname that is reduced to canonical
-- form equivalent to that of ksh(1), that is, symbolic link names are
-- treated literally when finding the directory name.  See @cd -L@ of
-- ksh(1).  Specifically, extraneous separators @(\"/\")@, dot
-- @(\".\")@, and double-dot @(\"..\")@ directories are removed.
reduceFilePath :: FilePath -> FilePath
reduceFilePath = joinPath . filePathComponents
This is in turn built on filePathComponents that does all the work.
...
filePathComponents :: FilePath -> [FilePath]
filePathComponents ""     = []
filePathComponents (c:cs) =
    reverse $ snd $ foldl accumulate
                          (if c == pathSeparator then ([],["/"]) else
([c],[]))
                          (cs++[pathSeparator])
    where
    accumulate :: (String,[String]) -> Char -> (String,[String])
    accumulate (cs, css) c =
        if c == pathSeparator
        then ([],(if null cs then id else cons cs) css)
        else (cs++[c],css)
    cons :: String -> [String] -> [String]
    cons cs css
        | cs == "." = css
        | cs /= ".." || null css = cs : css
        | otherwise =
          let hd = head css
              tl = tail css
          in if hd == [pathSeparator]
             then css
             else if hd == ".."
                  then cs : css
                  else if null tl
                       then ["."]
                       else tl
//

-- 
  Marcus D. Gabriel, Ph.D.                         Saint Louis, FRANCE
  http://www.marcus.gabriel.name            mailto:marcus@gabriel.name
  Tel: +33.3.89.69.05.06                   Portable: +33.6.34.56.07.75