[Haskell-cafe] Path names (again?)
Vincenzo aka Nick Name
vincenzo_mlRE.MOVE at yahoo.it
Thu Feb 5 22:44:42 EST 2004
Alle 19:13, giovedì 5 febbraio 2004, Glynn Clements ha scritto:
> > - concatenate file paths
> (concat . intersperse "/")
> Maybe you wanted something more, e.g. canonicalisation?
Yes, maybe an interface to realpath(3) is what I really need.
> > - tell if a path is absolute or relative
> ((== '/') . head)
> > - chase symlinks
> I was going to ask what you meant here but, AFAICT, Haskell (at
> least, GHC 5.04) doesn't appear to recognise the existence of
> symlinks. So, whatever you meant, the answer is probably "no".
I currently use module System.Posix from ghc6, there are stat and lstat
equivalents, what I want is to get the true file pointed from a symlink
after having known that it is a symlink, this can be done with
recursion of course, and it's trivial; I was just wondering if it was
implemented somewhere else, because I am not so expert in working with
filesystems and could make some mistake (e.g: I realized only recently
that using an hashtable of already visited files is necessary to avoid
ciclic links; also, without getting the canonical path, I could visit a
> > - find all the files in a directory (yes, that's what I need :))
> Define "file" (e.g. "regular file", "anything other than a
> directory", "directory entry" etc). Also, define "in"; i.e. are you
> talking about a recursive search (like "find")?
Yes, I forgot to say "recursively". I have an ocaml implementation but
it's prone to errors because of missing "canonicalization", so I did
not want to translate that in haskell for the same problem. Currently I
workarounded this all by forking "find", but it's prone to errors too
because I have no way to distinguish between newlines ending a file
name and newlines in the middle of a file name. I should put something
like "///" with "find -printf" at the end of each file name, and then
parse that, but it would really be preferable to code an haskell
library function equivalent to unix find.
> Recursion is a somewhat harder (maybe even impossible), given that
> doesDirectoryExist doesn't distinguish between a directory and a
> symlink to a directory, and the Posix module doesn't appear to
> include anything which would be of use (e.g. a binding for lstat()).
Yes, the System.Posix module in ghc6 has more features, but I still
don't like to handcode functions like "realpath"; if there is nothing
else maybe the best thing is to write a binding to this function (I
never did that but guess it's a one-liner), and to carefully read
source code for gnu find and implement it in haskell the same way.
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