Here is the latest Caml Weekly News, for the week of November 03 to 10, 2009.
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/b19555a7e09f063c#Thomas Gazagnaire announced:
We are pleased to announce the open-sourcing of the XAPI toolstack, written in OCaml, as used in the Citrix XenServer product line. The XAPI toolstack is licensed under the LGPL v2.1 with a special static linking exception. **context** Xen  is an open-source type 1 hypervisor, providing the ability to run multiple operating systems, called virtual machines, concurrently on a single physical processor. Type 1 (or native, bare-metal) hypervisors are software systems that run directly on host's hardware. They have been very popular architecture since the CP/CMS, developed at IBM in the 1960s. Citrix XenServer  is an enterprise-class, cloud-proven server virtualization platform that delivers the critical features of live migration and centralized multi-server management for Xen based virtual machine. XenServer is an open and powerful server virtualization solution that radically reduces datacenter costs by transforming static and complex datacenter environments into more dynamic, easy to manage IT service delivery centers. **xapi** The xapi toolstack, which provides the core Citrix Xenserver's functionalities, is a set of libraries and programs written in OCaml. It is approximately 200k lines of code developed from early 2006. Within Citrix, more than 40 people have already contributed to its source code. What the XAPI toolstack has to manage covers a large range, from low-level (interface with kernel and hypervisor) to high-level (distributed data/locking management). It also need to have good performance because it may be used in an environment of thousands of virtual machines per cluster and has to be able to run on systems with limited resources (embedded editions of Citrix XenServer are distributed on an USB stick and run in highly customized OS). Finally, as a major enterprise product, the XAPI toolstack evolves constantly, due to customer/business requests. The OCaml language has been particularly good so far to help us facing all this challenges, and we can't think of a better language to use :-) We really appreciate that the compiler tools are stable, that the compiled code is fast and small and that static-type inference makes our software robust to changes. **links** The released code is the current development version ("trunk") and is under active development. The repositories are here: http://xenbits.xen.org/xapi/xen-dist-ocaml.hg - scripts and Makefiles to build some external library dependencies http://xenbits.xen.org/xapi/xen-api-libs.hg - internal libraries (e.g. for talking to xenstore) http://xenbits.xen.org/xapi/xen-api.hg - the toolstack itself The easiest way to build the code is in a specially-prepared VM, instructions are here: http://xenbits.xen.org/xapi/install.html From now on, all development will take place on the firstname.lastname@example.org mailing list. In the future we plan to move relevant content such as documentation, designs, roadmaps etc. onto the main xen.org wiki. Comments, criticism and contributions are welcome! -- The XAPI toolstack team  http://xen.org  http://www.citrix.com/English/ps2/products/feature.asp?contentID=1686939
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/6b0998fcce38e25f#Hugo Ferreira announced:
If you like OcaIDE, please vote for it to show your support: http://marketplace.eclipse.org/node/599
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/5ace8ddf0af6701a#Aaron Bohannon asked and David Allsopp replied:
> I am quite confused by the whole process of compiling and installing > wrappers for C libraries. It seems like I can get things to work OK > without really knowing what I'm doing if everything is put and built > in a single directory. The hard part seems to be putting the right > files in the right places and getting the path arguments correct. > Then things stop working, and I have to really understand what's going > on, but the manual doesn't explain this part of the process in any > detail. Have a look at ocamlmklib in the manual - if it's available on your platform then it nicely hides away a lot of this. > Let's say I have a library "/opt/local/lib/libfoo.a" for which I want > to build and use a (native-code) OCaml wrapper. Here are the steps as > I understand them: > > 1) Write the file "foo_stubs.c" and compile it to get "foo_stubs.o". > > 2) Build the library "libfoo_stubs.a" by running > > ar rc libfoo_stubs.a foo_stubs.o > > 3) Copy "libfoo_stubs.a" to its permanent location, let's say, > "/usr/local/lib/ocaml/stubs/libfoo_stubs.a". > > 4) Write "foo.mli" and use it to build "foo.cmi" Steps 1-4 are fine. > 5) Write "foo.ml" and use it to build "foo.cmxa" by running > > ocamlopt -a -o foo.cmxa foo.ml > -ccopt -L/opt/local/lib -cclib -lfoo > -ccopt -L/usr/local/lib/ocaml/stubs -cclib -lfoo_stubs This command will also build foo.cmx, foo.a and foo.o > 6) Copy "foo.cmi" and "foo.cmxa" to their permanent location, let's > say "/usr/local/lib/ocaml/foo/" You should also copy foo.a to this directory which should fix the problem. foo.cmxa contains information required by OCaml but the actual code is in foo.a (as it's been natively compiled). Similarly, .cmx files contain information which ocamlopt needs but the actual code is in .o (or .obj) files. For native code, it's a code idea to copy the .cmx files too as it allows ocamlopt to do some inlining (I think that's right...) > 7) Write my file "bar.ml" that needs to use the library, and compile > it by running > > ocamlopt -I /usr/local/lib/ocaml/foo -o bar foo.cmxa bar.ml This should now work without error.Aaron Bohannon then said and Richard Jones replied:
> Ah! Yes, that's exactly the part I didn't understand and everything > works fine now. Thank you! > > I can't say I completely understand the byte-code case, but I don't > have an urgent need to. > > ocamlmklib seems fine, but if it's just a matter of saving keystrokes, > "make" does a pretty good job of that (as long as I know what to tell > "make" to do). For the install step, use 'ocamlfind install'. Grab the latest source tarball for one of our projects, eg. libvirt-ocaml, to see how we do it: http://libvirt.org/sources/ocaml/ or: http://libguestfs.org/download/
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/418b6809e94ea8bd#François Boisson announced:
Depuis quelque temps je maintiens des paquets camllight pour debian et ubuntu. Ces paquets se trouvent sur deb http://boisson.homeip.net/debian lenny divers (lenny peut être remplacé par woody, sarge (version 0.75) ou etch) deb http://boisson.homeip.net/ubuntu karmic divers karmic peut être remplacé par breezy, dapper edgy, feisty, gutsy, hardy, intrepid, jaunty. Ces paquets existent pour les architectures i386 et amd64 et vont des versions 0.75 à 0.80. La version 0.80 existent pour etch, lenny, hardy, intrepid, jaunty et karmic. Les sources permettant de faire ces paquets (assez «crades», c'était un de mes premiers paquets), se trouvent sur deb-src http://boisson.homeip.net/source/ ./ Par ailleurs, il y avait un bug dans la librairie graphique entrainant un segfault sur une architecture 64 bits si on faisait #open "graphics";; open_graph "";; (text_size "CAML");; cela entrainait une erreur de segmentation.. L'origine était un transtypage sauvage du à une décalration manquante de la fonction alloc_tuple. J'ai réglé le problème et ai fait des paquets corrigés pour lenny, karmic et hardy. (paquet camllight_0.80-1_amd64.deb).
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/1b613030e6a9be54#Jon Harrop said and Oleg replied:
> I did some experiments with MetaOCaml. Firstly, it is x86 only and not x64 > which means poor floating-point performance, many times slower than HLVM's. > The language itself is also very restrictive, e.g. you cannot generate > pattern matches dynamically so you cannot leverage the pattern match > compiler, which is a huge loss. In essence, effective use of MetaOCaml > requires writing in continuation passing style which OCaml and, therefore, > MetaOCaml do not handle well (closure invocations are slow in OCaml and CPS > is not optimized back into anything sane). So I do not consider MetaOCaml to > be a viable option for performance users. A few clarifications seems to be in order. First of all, the original poster asked about _offshoring_ with MetaOCaml. When the generated code is run with offshoring, a C of Fortran file is created, which can be compiled with your favorite compiler and dynamically linked back into the running OCaml program. Alternatively, you can use the generated C/Fortran code as it is, as a part of a C/Fortran project. We did exactly the latter in our FFT project: we used MetaOCaml to create C files for FFT kernels, and plugged the files into the FFTW benchmarking framework, which is pure C. It worked as expected. Because offshoring produces a portable C or Fortran code file, you can use the code on 32 or 64-bit platform. The reason the native MetaOCaml without offshoring does not work on amd64 is because at that time OCaml didn't emit PIC code for amd64. So, dynamic linking was impossible. That problem has long been fixed in later versions of OCaml. Offshoring is a good way to get around it, thanks Jan Kybic. Offshoring could just as well produce Verilog or LLVM code. Alas, we didn't get around to exploring that idea. Regarding continuation-passing style (CPS): if your code generatOR needs let-insertion, then the generatOR _may_ need to be encoded in CPS. The generatED code is _not_ in CPS; it is in the `conventional', so-called `direct style'. Even if we assume that CPS code is difficult to compile efficiently (which is not certain: in CPS, all `important' function calls are tail-calls, and OCaml is very good with tail-calls), that difficulty affects only the code generator rather than the generated code. Most of the time it is the generated code that is performance-critical. One may say that writing the generator in CPS is a bother. I have heard such objections. Please see our PEPM2009 paper about a way to address it http://okmij.org/ftp/Computation/Generative.html#circle-shift and write generators in the conventional style. Please see the example of writing a flexible Gaussian Elimination code, paying no penalty for abstractions. Fortunately, some people have considered MetaOCaml to be a viable option for performance users and have reported good results. For example, Tuning MetaOCaml Programs for High Performance Diploma Thesis of Tobias Langhammer. http://www.infosun.fmi.uni-passau.de/cl/arbeiten/Langhammer.pdf Here is a good quotation from the Introduction: ``This thesis proposes MetaOCaml for enriching the domain of high-performance computing by multi-staged programming. MetaOCaml extends the OCaml language. ... Benchmarks for all presented implementations confirm that the execution time can be reduced significantly by high-level optimizations. Some MetaOCaml programs even run as fast as respective C implementations. Furthermore, in situations where optimizations in pure MetaOCaml are limited, computation hotspots can be explicitly or implicitly exported to C. This combination of high-level and low-level techniques allows optimizations which cannot be obtained in pure C without enormous effort.''
Archive: http://groups.google.com/group/fa.caml/browse_thread/thread/a81606be6805729e#Wouter Swierstra asked and Pierre-Evariste Dagand replied:
> I've been learning OCaml, coming from a Haskell background. > While I'm familiar with functional programming, I am occasionally puzzled by > errors relating to the module system. That's normal, everyone does, at some point. Especially when you start having Parameterized Modules (called Functors in ML) all over the place. > I was wondering if there was a > comprehensive overview/tutorial of OCaml's module system. For a comprehensive source of information, there is the OCaml manual: http://caml.inria.fr/pub/docs/manual-ocaml/manual004.html For a tutorial on modules, I would recommend Chapter 14 of "Developing Applications With Objective Caml": http://caml.inria.fr/pub/docs/oreilly-book/html/index.htmlblue storm then added:
I'd also add : - the "formal" part of the manual (Part II) description of module types : http://caml.inria.fr/pub/docs/manual-ocaml/manual018.html . In particular the "Type specifications" section is quite informative imho. - the module-related chapter of the "UUU book" : http://caml.inria.fr/pub/docs/u3-ocaml/ocaml-modules.html If you're interested in theory, you can find an introduction to the ML Module system theory in the Pierce's book "Advanced topic in Types and Programming Languages" , and a some more advanced papers in the "A Few Paper On Caml" section of this website : http://caml.inria.fr/about/papers.en.html  http://books.google.com/books?id=A5ic1MPTvVsC&pg=PA293&dq=pierce+module+ML#v=onepage&q=pierce%20module%20ML&f=false
Thanks to Alp Mestan, we now include in the Caml Weekly News the links to the recent posts from the ocamlcore planet blog at http://planet.ocamlcore.org/. Core Gems: Time: http://ocaml.janestcapital.com/?q=node/73 Reflecting on One-Liners: http://alaska-kamtchatka.blogspot.com/2009/11/reflecting-on-one-liners.html Dyn alpha01: http://caml.inria.fr/cgi-bin/hump.cgi?contrib=714 Xapi toolstack: http://caml.inria.fr/cgi-bin/hump.cgi?contrib=713 The next server, please!: http://blog.camlcity.org/blog/ocamlnet3_ha.html ocamlbuild-plus: http://forge.ocamlcore.org/projects/ocamlbuildplus/
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