2002.12.17.txt

Hello,

Here is the latest Caml Weekly News, week 10 to 17 December, 2002.

1) opengl bindings without tcl/tk
2) Resource acquisition is initialization
3) mod_ocaml
4) maintainers for www.ocaml.org?
5) ocaml embedded scripting language
6) BDBFS version 0.3 release announcement

======================================================================
1) opengl bindings without tcl/tk
----------------------------------------------------------------------
Jean-Christophe Filliatre announced:

Olivier Andrieu writes:
> Jacques Garrigue:
> > LablGL does not really require labltk.  
> > It is just that when lablGL was first released, the only way to use
> > it was in combination with labltk. Now you can choose: labltk,
> > lablgtk, or Isaac Trotts lablglut.
> 
> It works with ocamlsdl too.

It's fun you mention it, since  I've just added the support for OpenGL
functions  in ocamlsdl  (it was  easy: one  flag and  one  function to
interface).  

I'm using the  lablGL bindings, without the tcl/tk  part. I've started
to port  the tutorials  by Jeff Molofee  (http://nehe.gamedev.net/) in
ocaml, in the subdirectory opengl/.

For  the impatient,  I've made  a tarball  with the  first  6 lessons,
available at:

        http://www.lri.fr/~filliatr/ftp/ocaml/ocamlsdl/

======================================================================
2) Resource acquisition is initialization
----------------------------------------------------------------------
Here are some extracts from the thread
http://caml.inria.fr/archives/200212/msg00125.html

Blair Zajac asked and Xavier Leroy answered:

> One of the nice things about C++ and Java is that with properly
> designed classes, you don't need to worry about freeing resources
> in complicated code, because the when the objects go out of scope
> either normally or via an exception, they will clean themselves up.

I believe this is a C++-specific idiom.  Java doesn't have
destructors, just finalizers that are called asynchronously by the
GC.  OCaml also has GC finalization (see below).

> Here's a good description of this idiom:
> 
> http://sourceforge.net/docman/display_doc.php?docid=8673&group_id=9028
> 
> Given that Ocaml has objects, it would be useful to have this
> idiom available to us.  Is there a way to implement it, rather
> than just waiting for the garbage collector?

Yes: higher-order functions.  For a file:

let with_file_in filename action =
  let ic = open_in filename in
  try
    let res = action ic in close_in ic; res
  with x ->
    close_in ic; raise x

For a mutex:

let synchronize mut action =
  try
    Mutex.lock mut;
    let res = action () in
    Mutex.unlock mut;
    res
  with x ->
    Mutex.unlock mut;
    raise x

You get the idea.

> Also, since objects have initializers, do they have finalizers?  I
> read the entire Oreilly book and didn't see any mention of them.
> 
> Reading the C code interface, it looks like you can associate a
> finalizer function to clean up an abstract type, but can you do
> this with normal Ocaml code?

Yes.  The function Gc.finalise lets you attach finalization code to any
heap-allocated Caml value, not just objects.  I'm not surprised it is
not mentioned in the O'Reilly book, since this is a recent addition to
the OCaml implementation.

Then Dmitry Bely asked and Xavier Leroy answered:

> Maybe I don't understand something but IMHO it's not very usable because
> with_file_in type is fixed after the first use. So e.g. input_line and
> input_char operation cannot be mixed. You cannot write something like
> 
> let process filename =
>   let f = with_file_in filename in
>      begin
>        print_string (f input_line);
>        print_char   (f input_char); (* syntax error! *)
>      end

Even without the typing problem, this would open and close the file
twice, which isn't what you want.  The correct usage is:

let process filename =
  with_file_in filename
    (fun ic ->
       print_string (input_line ic);
       print_char (input_char ic))

======================================================================
3) mod_ocaml
----------------------------------------------------------------------
Maxence Guesdon asked and Erik Arneson answered:

> I've been told about a mod_ocaml for apache, available at
> http://www.slacky.de/docs/projects/mod_ocaml/
> 
> I have not tested it, but I thought a lot of people might be interested.
> If some of you try it, can you tell us if it works ?

It works just fine!  It is a nice module for quick dynamic web pages,
like Mr Gushee pointed out, but I think there are a few changes that
could be made to make it safer and more robust for bigger applications.

First, it would be neat if there were a safer way to grab and validate
the query string.  A string replacement just doesn't work very well, and
it prints out an error if certain query string arguments aren't found,
so there's no easy way to just search for their existence.  There are
some OCaml modules out there to handle this, though, and I believe the
QUERY_STRING environment variable is still available for parsing.

Second, the OCaml interpreter is called every hit, which probably isn't
very scalable.  It would be really neat if the embedded OCaml page were
compiled to byte code and stored in memory somehow, so perhaps the OCaml
bytecode interpreter could only be called once.  Mod_perl does something
like this, and it seems to work very well.

The latter is a pretty big project, though.  I would have no idea where
to start, and I think mod_ocaml is a pretty neat beginning in any case! 

Then SooHyoung Oh added:

Ocaml Server Pages seems to have some of your requirements.

First, it receives and parses the query string.
Second, it compiles the ocaml script and execute the binary.

If someone has time to combine these two tools, it'll be great, isn't it?

ps: You can download osp from
http://www.rogare.com/index.php?inc=downloads/ocaml/ocaml,
and you can download some fixes and view examples from
http://www.taglib.co.kr/ocaml/index.html

======================================================================
4) maintainers for www.ocaml.org?
----------------------------------------------------------------------
Xavier Leroy called for volunteers:

Julian Assange, the creator and maintainer of the www.ocaml.org Web site,
is looking for a new maintainer to take care of that site.

As I understand it, this is a light job: just update the "News"
section and add or update some links when appropriate.  However, in
the interest of continuity, it would be good if the new maintainer
could commit for, say, a couple of years.

We (the OCaml team) could do the maintenance if we had to, but I like
the idea of a Caml site that is run by enthusiastic users...

If there are any volunteers, please contact me and I'll put you in
touch with Julian.

And, of course, many thanks to Julian for his efforts and support.

======================================================================
5) ocaml embedded scripting language
----------------------------------------------------------------------
Eric Merritt and Norman Ramsey answered:

> I was wondering if anyone is familiar with a little
> language implementation that is suitable to be
> embedded in an ocaml program. I realize that it
> wouldn't be that hard to do, especially in ocaml, but
> hate to duplicate work someone else has already done.
> There aren't really that many requirements, just the
> ability to look at passed in data structures a return
> a result based off of them. 
> 
> 
> At first I thought that ocaml itself would be the best
> scripting language but I havn't figured out how to link
> in code compiled with ocamlopt. In fact, I don't think
> it is possible at the moment. 

We've written an implementation of Lua, version 2.5, for Ocaml.
It's currently bundled with our nascent Quick C-- compiler at
http://www.cminusminus.org.  I'd like to split it out as a separate
distribution, but we're rather short of help at the moment and I'm
trying to get the papers written first.  Anyway, as far as I know
it's completely compatible with the C version, although a few library
functions are missing.  We've been fairly happy.

If you want to play with it, download and build Quick C--, then go to
the lua subdirectory and type `mk lua.ps'---that will give you the
documentation for the API.  The documentation for the language can
probably be had from lua.org, but if they don't keep manuals for old
versions, let me know and I'll put one in our CVS archive.

======================================================================
6) BDBFS version 0.3 release announcement
----------------------------------------------------------------------
Lex Stein announced:

I am pleased to announce the release of version 0.3 of the
BDBFS user-level NFS3 server (an NFS3 server written in OCaml).
You can get it here:

http://www.eecs.harvard.edu/~stein/bdbfs/

BDBFS is a portable, user-level NFS fileserver. It implements
version 3 of the NFS protocol as defined in RFC 1813.

BDBFS stands for Berkeley DataBase File System. BDBFS is
implemented in OCaml (release 3.06) and can be compiled either
to native code or bytecodes for the OCaml virtual machine. BDBFS
stores files, metadata (directories, inodes, the superblock) as
key:value pairs using the Berkeley Database (BDB) library.

It would be great to have some users (besides myself)!

This is a beta release. However, it passed all the
connectathon 2003 NFS3 tests and an hour of postmark
stress-testing.

======================================================================
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----------------------------------------------------------------------

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======================================================================

Alan Schmitt