Hello
Here is the latest Caml Weekly News, for the week of November 06 to 13, 2007.
I apologize for spamming this list to which I do not usually participate, but I would like to make you aware that Cilk Arts is hiring and that a good chunk of our development is done in Objective Caml. We are based in Lexington, MA, USA. Cilk Arts is a venture-backed startup originally founded by prof. Charles Leiserson and myself to bring to the marketplace the large body of research done at MIT on Cilk in the past 15 years. Some long-timers may remember that our Cilk team won the first International Contest on Functional Programming in 1998. We are big fans of ocaml (some of you may be familiar with my own work on FFTW). Our website http://www.cilk.com gives details about the company, products, and job positions. I would appreciate if you could forward this announcement to anyone whom you think could be interested.
I've been using Mathematica to render the graphs on our site, like the ray tracer language comparison: http://www.ffconsultancy.com/languages/ray_tracer/results.html What free OCaml software might I use to do the same thing?Till Varoquaux suggested:
There is an interface to gnuplot. I've never tried it: http://sourceforge.net/projects/ocaml-gnuplot/Hezekiah M. Carty also answered:
There is at least one partial plplot (http://plplot.sourceforge.net/) binding already in existence (http://vityok.org.ua/cgi-bin/odd.cgi/Ocaml-plplot), and I'm working on another one using camlidl rather than Swig. I haven't put my code out yet because I'd like to finish up some of the 3D plotting function wrappers first, but if you're interested in having something sooner I could put out what I have currently. There is enough there to do 2D plots, and the naming follows the C-library quite closely. The already-mentioned gnuplot binding seems to work reasonably as well, though I've only made very basic 2D plots with it. PsiLab (http://psilab.sourceforge.net/) is older, and based on OCaml 3.01 or 3.02 I think. But I've been able to get it to build on recent Linux distributions. It has a fairly high-level binding to the plplot libraries which is quite easy to use. I have dreams of some day updating it to work with recent OCaml releases. It might also be a decent start for a Mathematica-like toplevel with inline plots and so on if the toplevel customizations could be tied in to labltk or lablgtk. I don't know how possible this is though.Peng Zang also answered and Paul Pelzl added:
> I've used mlgrace in the past: > > http://www.eecs.umich.edu/~pelzlpj/mlgrace/ > > Although I've never tried labelled points before... I also have a convenience > interface to it that I've written so I can do stuff like: > > Plot.plotfun (( ** )2.) 0. 10. 0.1 "ro-";; > > and have it plot x^2 from 0 to 10 in 0.1 steps with a red line and dotted data > points. It's not packaged up nice at all, but I'm happy to share it if > you're interested. mlGrace does not currently expose an API to create point labels, but the xmgrace GUI can do this (under Plot->Set Appearance->Ann. values). So something similar to Jon's example plot could be generated using grace_view#plot_many, with a small amount of touch-up work from the GUI.
We are pleased to announce the public release of OCaml light, a formal semantics for a substantial, practical subset of the Objective Caml language. It is written in Ott, generating proof assistant definitions for HOL-4 and (in draft form) Coq and Isabelle/HOL. It comprises a small-step operational semantics and a syntactic, non- algorithmic type system. A type soundness theorem has been proved and mechanized using the HOL-4 proof assistant. To ensure that the operational semantics accurately models Objective Caml, an executable version of the semantics has been created (and proved equivalent in HOL to the original, relational version) and tested on a number of small test cases. For more information please visit http://www.cl.cam.ac.uk/~so294/ocaml.
> Segfaults in OCaml are seldom, but nevertheless
> those seldom seen segfaults should be fixed.
> The original poster stated out that the bug he
> posted was four months on status "new".
> This was a littlebid astonishing, and possibly
> the reason why this thread was started.
I think this is my fault: I implemented Scanf in the first place.
May be some of you missed the point in the segfault example involving Scanf
that was given on this list: the example involves using positional parameters
in the string argument passed to sscanf and using meta format specifications
in the format string argument.
Positional parameters:
----------------------
Positional parameters are parameters number specifications that allows format
strings to refer to another parameter than the next in the presentation
order. This is supposed to be useful for internationalization where you can
change the printing order of the parameters to reflect the translation.
This new feature has only been introduced in the documentation for Printf
just after the successful correction of the long standing strange behaviour
of printf with respect to partial evaluation. Positional parameters have
never been mentioned in the Scanf documentation and Scanf is not supposed
to supported them.
To say the least, this feature is still experimental and not yet completely
implemented in the current sources of the compiler. In fact, the typechecker
abruptely rejects format strings with positional parameters, as exemplify
here:
# Printf.printf "%2$i %1$s" "toto" 1;;
Bad conversion %$, at char number 0 in format string ``%2$i %1$s''
As mentioned above, Scanf is not supposed to handle positional parameters,
and indeed rejects them at runtime in the format string (this could seem
overkill, given that the type-checker rejects positional parameters in the
first place, but well, 2 checks are better than one!).
Meta format specifications:
---------------------------
However, Scanf is still capable to read a format string lexem given in the
input, provided the format used to read this lexem involves a meta format
that properly describes the format string lexem to be read. For instance:
Scanf.sscanf s "%{ %i %f %}" is supposed to read in the input (the string s)
a format string that specify to read first an integer, then a floating point
number.
A more practical working example could be:
# let fmt =
Scanf.sscanf "\"Reference: %i Price : %f\"" "%{%i%f%}"
(fun fmt -> fmt);;
val fmt : (int -> float -> '_a, '_b, '_c, '_d, '_d, '_a) format6 = <abstr>
# string_of_format fmt;;
- : string = "Reference: %i Price : %f"
This features allows a procedure to read the format string it has to use to
read a file: the procedure just reads the format as the first line of the
file.
The example seg-fault analysis:
-------------------------------
So, the seg-faulting example given is quite involved, since it uses scanf's
capability to read a format string in the input, in order to create a format
string with positional specification. This was clearly unexpected, given the
``axiom'' that says "the type checker will prevent that in the first place
since it rejects any positional parameter!". In this case, the typechecker
cannot reject the format string given in the program, since it has no
positional specification; and it cannot reject the format read, since this
format is unknown at compile time!
This simply means that there is a bug in the type compatibility runtime test
for format strings that fails to properly reject positional parameters. This
is not difficult to correct, if not at all satifactory.
The corrections or problem suppression:
---------------------------------------
I once thought that introducing positional parameters in Scanf, Printf, and
Format, would be a piece of cake in comparison to correcting the hard bug of
printf's treatment of partial evaluation (this ``misfeature'' stood there for
more than 10 years, before a correction can be figured out). Unfortunately, I
was wrong, positional parameters are not at all easy, even when the printf
behaviour is corrected: admittedly, the runtime implementation for positional
parameters was not too hard for Printf and it has been done quickly; on the
other hand, the type checking of format strings with positional parameters
proved to be untrivial: you need a deep breath to dig into the old code, you
need once more understand it in depth, and basically you must rewrite it with
a new logic that supports positional parameters. This has not yet been done,
unfortunately.
In conclusion, I have to correct the runtime compatibility check for formats
to suppress the problem, and remove any mention of positional parameters from
the documentation, until I achieve the new type checking stuff for format
strings.
Or just give up on this complex feature that has already upset too many people.
I agree with any one who cares that I was wrong to introduce a not yet
properly baked feature in Caml. The natural over optimistic tendancy of my
researcher's enthousiasm caught me there ...
[...]
> I for myself have only stated that I hope the bugs will be fixed.
I hope them to be fixed as well. Sometimes it's difficult. Sometimes we lack
the time and concentration to find the solution. Even worse, sometimes we
never find the solution for years...
Best regards,
PS: You can check in the bug tracking system that there are more than one
message concerning positional parameters in format strings, and that I
already answered to a lot of them.
Wink Technologies, Inc., the makers of the soon-to-be-famous people search engine (http://wink.com), have just released another OCaml library, this time for caching data: "Cache implements a caching service for storing arbitrary strings that can be located by string keys. The caching service is reachable over TCP. The cache can be distributed over several nodes. The cache can be saved to disk in regular intervals. A client module is included. Both synchronous and asynchronous access methods are defined." Downloadable at http://oss.wink.com/cache/. There is also a manual: http://oss.wink.com/cache/cache-1.0/doc/html/index.html There is also a GODI package for it (godi-cache). N.B. The library has been in production for more than a year. It's rock-stable and fast, and runs 24x7 without any problems.Joel Reymont asked and Gerd Stolpmann answered:
> Why did you guys roll your own instead of using memcached? We considered using memcached. However, there is no client for OCaml, and especially no asynchronous client, so we would have had to write one. I looked at the protocol, and it turned out to be weird, ad-hoc, and not very extensible. It would have been no fun developing such a client. In contrast, for developing our own caching server, it was not necessary to write any new networking code: By using the SunRPC library of Ocamlnet we got the whole communication stuff for free, and the protocol is now well-structured and easily extensible. Furthermore, we could tailor the features to our requirements, and have the guarantee that we can adapt the server to any changes. Actually, we needed only 1 day for developing the library, and another day for integrating it. This is what other companies spend for evaluating external software they might want to use. So the costs were justified, and we now have exactly the software we wanted. So the essence is: By using good tools (OCaml, Ocamlnet, etc.) we can develop the software ourselves with the same costs as the integration of an external component would have taken. Plus, we have perfectly adapted software, and are on the safe side for the future. Sounds like a good deal, right?
> I have a fairly substantial OCaml application that leaks memory. > What tools or techniques do people use to track down memory leaks? > Minimally, is there a way to enumerate the live objects in the heap? There's ocaml-memprof, a compiler patch that adds memory profiling features to ocaml programs; Latest update of the patch itself, as far as I know: http://www.pps.jussieu.fr/~smimram/docs/ocaml-3.09.3-memprof.patch Readme: http://www.pps.jussieu.fr/~smimram/docs/README.memprof
findlib-1.2 is available. This version focuses on supporting Camlp4-3.10 properly, and making it work on Win32. There are also a few other fixes and enhancements. For Camlp4 there are now special packages that match the available extensions on O'Caml 3.10. For example, you can now request -package camlp4.listcomprehension to enable the list comprehension extension. The Win32 fixups have only been tested with the mingw port of O'Caml. Please read the INSTALL instructions carefully. For general information about findlib, see http://www.ocaml-programming.de/programming/findlib.html A full list of changes can be found inside http://www.ocaml-programming.de/packages/documentation/findlib/README.html The new tarball is available under http://www.ocaml-programming.de/packages/findlib-1.2.tar.gz
Here is a quick trick to help you read this CWN if you are viewing it using vim (version 6 or greater).
:set foldmethod=expr
:set foldexpr=getline(v:lnum)=~'^=\\{78}$'?'<1':1
zM
If you know of a better way, please let me know.
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