Here is the latest OCaml Weekly News, for the week of May 09 to 16, 2017.
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00036.htmlChristoph Höger said and Oleg replied:
> Assume a simple OCaml program with two primitives that can cause > side-effects: > let counter = ref 0 > let incr x = counter := !counter + x ; !counter > let put n = counter := n; !counter > put (5 + let f x = incr x in f 3) > This example can be transformed into a pure program using a counter > monad (using ppx_monadic syntax): > do_; > i <-- let f x = incr x in f 3 ; > p <-- put (5 + i) > return p > For a suitable definition of bind and return, both programs behave > equivalently. My question is: How can one automatically translate a > program of the former kind to the latter? More recently (Apr 29), Yaron Minsky, contrasting his view with the moderate position by Anil Madhavapeddy, spoke very highly about monads. One really wonders why this obsession with monads. Why to use monadic encoding if effects can be expressed directly? Is really > do_; > i <-- let f x = incr x in f 3 ; > p <-- put (5 + i) > return p so much better than let res = put (int 5 + let f x = incr x in f 3) ? One can say that the do-notation lets us use the other ways to implement counters. Well, so does the direct notation: let res = put (int 5 + let f x = incr x in f 3) This is truly OCaml code, with no PPX or other pre-processors. It all depends on how the `primitives' int, put, incr are defined. They can use a reference cell or pass the state or talk to a remote computer via some RPC. If we abstract over the primitives, the same expression can be evaluated with different models of `counters'. Incidentally, we did not have to abstract over `let' in this example. And we did not have to abstract over functions. Very often our DSL can be kept to first order. Embedding into expressive OCaml compensates. Incidentally, types really help to tell which expression belongs to which `level' -- effectful DSL or OCaml (which acts as a higher-order, typed `macro' language). The recent article http://okmij.org/ftp/tagless-final/nondet-effect.html presents quite a bit more challenging example, of non-determinism. Once can write literally Curry (*) code in OCaml -- with no PPX or other preprocessors, using multiple interpretations of non-determinism. All works in vanilla OCaml 4.04. We don't have to put up with functors: first-class modules really help. The modular implicits will help even more, by putting the `implementation' argument out of sight. (*) Curry is a functional-logic programming language, with built-in non-determinismYaron Minsky then said:
I like monadic encodings of concurrency because they make the places at which interleavings can occur explicit in the types and the code. What I've seen from more direct encodings does not have this killer feature. I don't want to go back to the world of mutexes and semaphores... Maybe some version of algebraic effects plus appropriate tracking in the type system will solve all the problems. But for now, I like my monads.
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00037.htmlAlexey Egorov announced:
I'd like to announce first release of Clarity - the library that tries to make pure functional programming idioms as useful as possible given OCaml's absence of higher-kinded types and typeclasses. It features some well-known "classes" like Functor, Applicative and Monad along with concrete instances and utility functions. GitHub page - https://github.com/IndiscriminateCoding/clarity Also you can install it from opam-repository.
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00051.htmlJeremie Dimino continued this old thread:
Coming back to this thread. I had a simple idea recently for a ppx that makes it easy to do pattern matching on abstract types. I wrote some experiments here . This essentially allows to make the AST fully abstract while still being able to deconstruct it conveniently. In fact the patterns are even nicer than ones matching the raw data type directly since you can build your own helper patterns. Making the AST abstract will allow to make the API evolve in a backward compatible way even though the underlying AST keeps changing. I just did some experiments for now. I think we'll eventually implement this solution properly and use it in our ppx code.  https://github.com/diml/ppx_view_pattern
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00070.htmlAnil Madhavapeddy announced:
Firstly, thank you to Marshall for kicking off this discussion. It seems clear from the discussion that there is a desire for an asynchronous, modern mailing-list style communications mechanism for the community. There are several other more synchronous chat-based solutions (IRC, Slack, Gitter), but Discourse stood out as as an open-source forum that is successfully used by other communities such as Rust . Therefore, I have set up a hosted Discourse instance at http://discuss.ocaml.org as an experimental service, and now need your help to decide whether or not this is a viable longer term solution for our community. It is open to signups, and we have two immediate things to do: - Decide how to organise the categories in the site  - A timeline for shifting various ocaml.org services over to this  Most immediately, as we decide on categories, we need volunteers to help nurture the site and keep an eye on their areas. Globally, there are currently two administrators (Gabriel Scherer and myself), and we can expand access controls as the site comes into its own. It is open to public signups immediately, so please do give it a try. Bear in mind that as it is experimental, it is probably a good idea to expect some rearrangements of the configuration in the next few weeks. Anyone interested is extremely welcome to comment on the existing topics below with their opinions, or to begin a new one as appropriate.  Gabriel Scherer did the research the last time this topic came up! https://users.rust-lang.org/t/what-are-rusts-discourse-hosting-plans-and-time-requirement/6462  http://discuss.ocaml.org/t/which-categories-to-create-in-the-site/19  http://discuss.ocaml.org/t/discussion-site-status-and-timeline/23
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00078.htmlMalcolm Matalka announced:
Snabela 1.0 is released today (thanks to Anil for several back and forths). Snabela is a logic-less template system loosely based on Mustache but attempting to fix some issues I had with Mustache. To install Snabela simply do: opam install snabela Snabela is a spec, a library, and a CLI tool to evaluate templates. Some features Snabela has: - It supports applying arbitrary transformers to the values being replaced. This is useful for ensuring values are escaped, representing numeric values as money, applying locales, capitalizing text, etc. - Like Mustache, it has sections for iterating over lists and conditionally applying a portion of a template. - Unlike Mustache, Snabela is strict-by-default, in that a missing value, or the wrong type in a test is an error. - Snabela supports escaping the template code, which is @ by doing @@. - Snabela is meant to be implementable in a wide array of languages and the language is meant to be small. You can find a gentle introduction to Snabela here: http://blog.appliedcompscilab.com/snabela-release/index.html If you run into any issues with Snabela, please don't hesitate to make an issue here: https://bitbucket.org/acslab/snabela/issues
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00083.htmlAnton Bachin announced:
Lwt is making an effort to become more reader- and contributor-friendly. https://github.com/ocsigen/lwt/pull/354 To summarize, from the PR: the core, lwt.ml, has been reorganized to make it more readable. It has been equipped with thorough comments, including a friendly overview of all concepts used by the core. We hope this change opens Lwt up to more contributions of all kinds. It should unblock major upcoming work, such as porting Lwt to multicore effects. Understanding Lwt better also makes it possible to write the much-promised new manual. The new Lwt core is meant to be a permanent work in progress: if you don't understand it, or find that something in it is *still* written in a confusing way, please ask/let the Lwt maintainers know. We *want* to help readers understand, and to improve that code! And, anyway, your query will very likely teach *us* something. Any review of the PR would be very helpful, to Lwt and to all of its users – even if you read only to find typos. Also, if you have access to a stress test, it would be very useful to put the refactored core through the paces. There are instructions at the bottom of the PR. If the stress test is open source, maybe we can use it as a guide for writing a stress test specifically for Lwt, because Lwt really needs to have at least one of those.
Archive: https://sympa.inria.fr/sympa/arc/caml-list/2017-05/msg00085.htmlGabriel Scherer said:
This is a gentle reminder that the presentation submission deadline for the OCaml workshop 2017 on May 31st, in two weeks. (For the details, the original announcement at the end of this email.) Writing a talk proposal is not very difficult (you can do it in 20-30 minutes), no need to wait for the last minute! https://icfp-ocaml17.hotcrp.com/ If you have any question about the workshop, feel free to send me an email. If you know someone whose work would be of interest to the OCaml community, please encourage them to propose a presentation. The workshop is a unique (yearly) even to meet other people of the OCaml community whose work may have been supporting your own, or building on top of it. The programme of the ICFP conference is now available. For a sneak peek, some of the preprints are already available (https://github.com/gasche/icfp2017-papers). Besides the ICFP conference, many co-located events may also be of interest to the caml-community. See the list of events on the ICFP webpage (ML-family languages, Haskell, Scheme, Erlang, type-directed programming, effectful programming, high-performance computing, art and music). http://icfp17.sigplan.org/home For the more theory-oriented among us, the co-located FSCD conference also have many nice events (linear logic, unification, security, higher-dimensional rewriting, homotopy type theory, string diagrams, proof theory, confluence, logical frameworks, program rewriting): http://www.cs.ox.ac.uk/conferences/fscd2017/ Finally, if you are a student (or are a teacher with students), you should consider sending application(s) to the Programming Language Mentoring Workshop (http://icfp17.sigplan.org/track/PLMW-ICFP-2017), who can fund conference attendance to university student ( the main target is undergraduate and young graduate, corresponding to the bachelor/master cycles in Europe ). ACM also has various forms of financial support available, in particular for students that give a presentation; see http://www.sigplan.org/PAC/. Call for presentations OCaml 2017 The OCaml Users and Developers Workshop September 8th, 2017, Oxford, UK, Co-located with ICFP 2017 http://ocaml.org/meetings/ocaml/2017/ Talk proposal submission deadline: May 31st, 2017 (Please redistribute widely.) The OCaml Users and Developers Workshop brings together the OCaml community, including users of OCaml in industry, academia, hobbyists and the free software community. Previous editions have been colocated with ICFP 2012 in Copenhagen, ICFP 2013 in Boston, ICFP 2014 in Gothenburg, ICFP 2015 in Vancouver and ICFP 2016 in Nara, following the OCaml Meetings in Paris in 2010 and 2011. OCaml 2017 will be held on September 8th, 2017 in Oxford, UK, colocated with ICFP 2017 and FSCD 2017. http://conf.researchr.org/home/icfp-2017 http://www.cs.ox.ac.uk/conferences/fscd2017/ Scope ----- Presentations and discussions will focus on the OCaml programming language and its community. We aim to solicit talks on all aspects related to improving the use or development of the language and its programming environment, including, for example (but not limited to): - compiler developments, new backends, runtime and architectures - practical type system improvements, such as (but not limited to) GADTs, first-class modules, generic programming, or dependent types - new library or application releases, and their design rationales - tools and infrastructure services, and their enhancements - prominent industrial or experimental uses of OCaml, or deployments in unusual situations. Presentations ------------- It will be an informal meeting with no formal proceedings. The presentation material will be available online from the workshop homepage. The presentations may be recorded, and made available at a later time. The main presentation format is a workshop talk, traditionally around 20 minutes in length, plus question time, but we also have a poster session during the workshop -- this allows to present more diverse work, and gives time for discussion. The program committee will decide which presentations should be delivered as posters or talks. Submission ---------- To submit a presentation, please register a description of the talk (about 2 pages long) at https://icfp-ocaml17.hotcrp.com/ providing a clear statement of what will be provided by the presentation: the problems that are addressed, the solutions or methods that are proposed. LaTeX-produced PDFs are a common and welcome submission format. For accessibility purposes, we ask PDF submitters to also provide the sources of their submission in a textual format, such as .tex sources. Reviewers may read either the submitted PDF or the text version. Important dates --------------- Wednesday 31st May (any time zone) Abstract submission deadline Wednesday 28th June Author notification Friday 8th September 2017 OCaml Workshop ML family workshop and post-proceedings --------------------------------------- The ML family workshop, held on the previous day, deals with general issues of the ML-style programming and type systems, focuses on more research-oriented work that is less specific to a language in particular (OCaml). There is an overlap between the two workshops, and we have occasionally transferred presentations from one to the other in the past. The authors who feel their submission fits both workshops are encouraged to mention it at submission time and/or contact the Program Chairs. We are planning to publish combined post-proceedings and to invite interested authors of selected presentations to expand their abstracts for inclusion. Program Committee ----------------- Ashish Agarwal, Solvuu, USA François Bobot, CEA, France Frédéric Bour, OCaml Labs, France Cristiano Calcagno, Facebook, UK Louis Gesbert, OcamlPro, France Sébastien Hinderer, INRIA, France Atsushi Igarashi, Kyoto University, Japan Oleg Kiselyov, Tohoku University, Japan Julia Lawall, INRIA/LIP6, France Sam Lindley, The University of Edinburgh, UK Louis Mandel, IBM Research, USA Zoe Paraskevopoulou, Princeton University, USA Gabriel Scherer, Northeastern University, USA Questions and contact --------------------- Please send any questions to the chair: Gabriel Scherer firstname.lastname@example.org
Here is a sneak peek at some potential future features of the Ocaml compiler, discussed by their implementers in these Github Pull Requests. - Make assertions nonexpansive https://github.com/ocaml/ocaml/pull/1142 - move overriding class definitions to language reference chapter https://github.com/ocaml/ocaml/pull/1153 - Don't use the page table when scanning closures https://github.com/ocaml/ocaml/pull/1156 - updated description for printf "%g" https://github.com/ocaml/ocaml/pull/1163 - document operators' associativity and precedence level https://github.com/ocaml/ocaml/pull/1167
Here are links from many OCaml blogs aggregated at OCaml Planet, http://ocaml.org/community/planet/. Proving a mem/map property http://blog.shaynefletcher.org/2017/05/proving-mem-map-property.html New opam features: more expressive dependencies http://www.ocamlpro.com/2017/05/11/new-opam-features-more-expressive-dependencies/
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