Here is the latest OCaml Weekly News, for the week of May 24 to 31, 2016.
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2016-05/msg00218.htmlFrançois Pessaux announced:
It is my pleasure to announce the new release for FoCaLiZe (the 0.9.1 version). A certain number of bugs found in the focalizec compiler have been fixed. The generated code is slightly lighter. Termination proofs for recursive functions, in addition to the previously available structural way, can be now written using a measure or a well-founded relation. A complete description of changes / new features can in found in the CHANGES file of the distribution. The 0.9.1 release is available from focalize.inria.fr at http://focalize.inria.fr/download/focalize-0.9.1.tgz Uncompress, extract, then read the INSTALL file in the newly created directory focalize.0.9.1 and follow the simple instructions written there. A public GIT repository is also available, allowing to fetch the latest development state of FoCaLiZe. However, its content is not bullet-proof and may be unstable at some times. It reflects the real-time state of FoCaLiZe and may bring fixes and features not available in previous releases and that will be part of the next release. To clone the current FoCaLiZe GIT repository, invoke: git clone http://focalize.inria.fr/focalize.git This will create a focalize repository in your current directory. Once cloned, it is possible to fetch updates with the usual GIT commands (essentially git pull origin master). Note that this access being public, it doesn't allow pushing (i.e. submitting) modifications done in the sources tree. To join people and discussions write to firstname.lastname@example.org. Implementors also listen to suggestions (and compliments if some ^_^) at the mail address: email@example.com. Enjoy. For the entire FoCaLiZe implementation group, François Pessaux. May 2016 What is it FoCaLiZe ? --------------------- FoCaLiZe is an integrated development environment to write high integrity programs and systems. It provides a purely functional language to formally express specifications, describe the design and code the algorithms. Within the functional language, FoCaLiZe provides a logical framework to express the properties of the code. A simple declarative language provides the natural expression of proofs of properties them from within the program source code. The FoCaLiZe compiler extracts statements and proof scripts from the source file, to pass them to the Zenon proof generator to produce Coq proof terms that are then formally verified. The FoCaLiZe compiler also generates the code corresponding to the program as an Objective Caml source file. This way, programs developed in FoCaLiZe can be efficiently compiled to native code on a large variety of architectures. Last but not least, FoCaLiZe automatically generates the documentation corresponding to the development, a requirement for high evaluation assurance. The FoCaLiZe system provides means for the developers to formally express their specifications and to go step by step (in an incremental approach) to design and implementation, while proving that their implementation meets its specification or design requirements. The FoCaLiZe language offers high level mechanisms such as inheritance, late binding, redefinition, parametrization, etc. Confidence in proofs submitted by developers or automatically generated ultimately relies on Coq formal proof verification. FoCaLiZe is a son of the previous Focal system. However, it is a completely new implementation with vastly revised syntax and semantics, featuring a rock-solid infrastructure and greatly improved capabilities.
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2016-05/msg00219.htmlGabriel Scherer announced:
You may be interested in the following blog post, in which I give instructions to measure the worst-case latencies incurred by the GC: Measuring GC latencies in Haskell, OCaml, Racket http://prl.ccs.neu.edu/blog/2016/05/24/measuring-gc-latencies-in-haskell-ocaml-racket/ In summary, the commands to measure latencies look something like: % build the program with the instrumented runtime ocamlbuild -tag "runtime_variant(i)" myprog.native % run with instrumentation enabled OCAML_INSTR_FILE="ocaml.log" ./main.native % visualize results from the raw log $(OCAML_SOURCES)/tools/ocaml-instr-graph ocaml.log $(OCAML_SOURCES)/tools/ocaml-instr-report ocaml.log While the OCaml GC has had a good incremental mode with low latencies for most workloads for a long time, the ability to instrument it to actually measure latencies is still in its infancy: it is a side-result of Damien Doligez's stint at Jane Street last year, and 4.03.0 is the first release in which this work is available. A practical consequence of this youth is that the "user experience" of actually performing these measurements is currently very bad. The GC measurements are activated in an instrumented runtime variant (OCaml supports having several variants of the runtime available, and deciding which one to use for a specific program at link-time), which is the right design choice, but right now this variant is not built by default by the compiler distribution -- building it is a configure-time option disabled by default. This means that, as a user interested in doing the measurements, you have to compile an alternative OCaml compiler. Furthermore, processing the raw instrumented log requires tool that are also in their infancy, and are currently included in the compiler distribution sources but not installed -- so you have to have a source checkout available to use them. In contrast, GHC's instrumentation is enabled by just passing the option "+RTS -s" to the Haskell program of interest; this is superbly convenient and something we should aim at. I discussed with Damien whether we should enable building the instrumented runtime by default (for example pass the --with-instrumented-runtime option to the opam switches people are using, and encourage distributions to use it in their packages as well). Of course there is a cost/benefit trade-off: currently virtually nobody is using this instrumentation, but enabling it by default would increase the compilation time of the compiler distribution for everyone. (On my machine it only adds 5 seconds to total build time.) I personally think that we should aim for a rock-solid experience for profiling and instrumenting OCaml program enabled by default¹. It is worth making it slightly longer for anyone to install the compiler if we can make it vastly easier to measure GC pauses in our program when the need arises (even if it's not very often). But that is a discussion that should be had before making any choice. Regarding the log analysis tools, before finding about Damien's included-but-not installed tools (a shell and an awk script, in the finest Unix tradition) I built a quick&dirty OCaml script to do some measurements, which can be found in the benchmark repository below. It would not be much more work to grow this in a reusable library to extract the current log format into a structured data structure -- the format is undocumented but the provided scripts in tools/ have enough information to infer the structure. Such a script/library would, of course, remain tightly coupled to the OCaml version, but I think it could be useful to have it packaged for users to play with. https://gitlab.com/gasche/gc-latency-experiment/blob/master/parse_ocaml_log.ml ¹: We cannot expect users to effectively write performant code if they don't have the tool support for it. The fact that lazyness in Haskell makes it harder for users to reason about efficiency or memory usage has made the avaibility of excellent performance tooling *necessary*, where it is merely nice-to-have in OCaml. Rather ironically, Haskell tooling is now much better than OCaml's in this area, to the point that it can be easier to write efficient code in Haskell. Three side-notes on profiling tools: 1. `perf record --call-graph=dwarf` works fine for ocamlopt binaries (no need for a frame-pointers switch), and this is documented: https://ocaml.org/learn/tutorials/performance_and_profiling.html#UsingperfonLinux 2. Thomas Leonard has done excellent work on domain-specific profiling tools for Mirage, and this is the kind of tool support that I think should be available to anyone out of the box. http://roscidus.com/blog/blog/2014/08/15/optimising-the-unikernel/ http://roscidus.com/blog/blog/2014/10/27/visualising-an-asynchronous-monad/ 3. There is currently more debate than anyone could wish for around a pull request of Mark Shinwell for runtime support for dynamic call graph construction and its use for memory profiling. https://github.com/ocaml/ocaml/pull/585 4. Providing a good user experience for performance or space profiling is a fundamentally harder problem than for GC pauses. It may require specially-compiled versions of the libraries used by your program, and thus a general policy/agreement across the ecosystem. Swapping a different runtime at link-time is very easy.
Here is a sneak peek at some potential future features of the Ocaml compiler, discussed by their implementers in these Github Pull Requests. Do not perform compaction if the real overhead is less than expected https://github.com/ocaml/ocaml/pull/590 Manual: New chapter on polymorphic types and functions in the tutorial https://github.com/ocaml/ocaml/pull/594
Here are links from many OCaml blogs aggregated at OCaml Planet, http://ocaml.org/community/planet/. Odepack 0.6.7 released http://forge.ocamlcore.org/forum/forum.php?forum_id=933 Full Time: Software Developer (Functional Programming) at Jane Street in New York, NY; London, UK; Hong Kong http://jobs.github.com/positions/0a9333c4-71da-11e0-9ac7-692793c00b45
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