Re: Recursive Sets?

[Markus Mottl <mottl@miss.wu-wien.ac.at>]

On Wed, 02 Aug 2000, Michael Welsh Duggan wrote:
> I have been trying to create a recursive type which can express sets
> of itself.  The following code is not meant to be correct (it isn't),
> but hopefully expresses the sort of thing I want to do.  Can someone
> throw some ideas at me?

I am afraid, but it is not possible to have mutually recursive module
and type definitions. See the following entry in the archive:

  http://pauillac.inria.fr/bin/wilma_hiliter/caml-list/199901/msg00016.html?line=47#hilite

I don't know what exactly you want to do. Some time ago I implemented a
referentially transparent directory service that might be similar to what
you want to implement, e.g.:

                         +-root-+
                        /  |  |  \
                      a    b  \   c
                      |   /    f
                      d  e    /|\
                             g h i

It is possible to update nodes directly without losing persistence. E.g.:

  let dir1 = (* directory as above,
                the "current working directory" is "root" *) in
  let dir2 = Dir.cd_path dir1 ["f"; "h"; "x"] ...

This will keep "dir1" unchanged, but "dir2" will look as follows (the
CWD will be "root/f/h/x"):

                         +-root-+
                        /  |  |  \
                      a    b  \   c
                      |   /    f
                      d  e    /|\
                             g h i
                               |
                               x

You can parameterize the directory over arbitrary ordered elements. If it
is something like this you need, I could place it online (though, it is
part of a larger project that I'll release in a few weeks, anyway - not
much time right now)...

Regards,
Markus Mottl

-- 
Markus Mottl, mottl@miss.wu-wien.ac.at, http://miss.wu-wien.ac.at/~mottl