December 2016 - Haskell-Cafe

Multi groupby with foldl' and Map.insertWithKey
by Cody Goodman 28 Dec '16

28 Dec '16

My goal is to take data like this: [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] and build a Map like this: [("MA",[("Pregnancy",1)]),("TX",[("Alcohol",2)])] Here is my failed attempt: {-# LANGUAGE ScopedTypeVariables, BangPatterns #-} import qualified Data.Map as M import Data.List (foldl') import Data.Maybe import Debug.Trace data Info = Info { i :: !Int, healthTopic :: !String, state :: !String } deriving Show m :: M.Map String (M.Map String Integer) m = M.fromList [("MA", M.fromList[("Pregnancy",1)]),("TX", M.fromList[("Alcohol",2)])] constantValsPerState = foldl' (\accum currentRow -> do M.insert (state currentRow) "xxx" accum ) M.empty [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] -- λ> constantValsPerState -- fromList [("MA","xxx"),("TX","xxx")] -- how can I get something like: -- λ> numTopicsPerState -- fromList [("MA", fromList[("Pregnancy",1)]),("TX", fromList[("Alcohol",2)])] -- so we need to give the modified stae of the new map isntead of M.empty -- λ> m -- fromList [("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",2)])] -- λ> M.insertWith (\new old -> new) "MA" M.empty m -- fromList [("MA",fromList []),("TX",fromList [("Alcohol",2)])] numTopicsPerState = foldl' (\(accum :: M.Map String (M.Map String Integer)) currentRow -> do M.insertWithKey (\k new old -> M.insert (healthTopic currentRow) ((fromMaybe 0 $ M.lookup (healthTopic currentRow) old) + 1) new ) (state currentRow) (fromMaybe (M.empty) (M.lookup (state currentRow) accum)) accum ) M.empty [ Info 0 "Alcohol" "TX" , Info 1 "Alcohol" "TX" , Info 2 "Pregnancy" "MA" ] -- WRONG OUTPUT -- λ> numTopicsPerState -- fromList [("MA",fromList []),("TX",fromList [("Alcohol",1)])] -- TODO -- turn -- fromList [("Alcohol",fromList []),("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",2)])] -- into -- fromList [("MA",fromList [("Pregnancy",1)]),("TX",fromList [("Alcohol",3)])]

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Call for new Stackage Curator
by Michael Snoyman 26 Dec '16

26 Dec '16

I'm copying the text from my blog post today[1]. On behalf of the Stackage curators, I'm putting out a call for a volunteer to join the team. The Stackage curators are responsible for the day-to-day management of the Stackage project: merging PRs, managing builds, reporting bounds issues and build or test failures, and every once in a while making a judgement call on when to bump to newer package versions. The curator team currently consists of Adam Bergmark, Dan Burton, Jens Petersen, and me. The processes we follow are documented in the curator guide[2]. We each rotate shifts, taking one week at a time on duty. Overall, the workload is light and straightforward: usually less than 30 minutes a day. We're putting out this call for a new volunteer since we've been running as a four-person show for a while now, and want to make sure we're getting our processes well documented enough for newcomers to easily come up to speed on the process. While we are currently asking for just one new addition to the team, if there are multiple enthusiastic candidates, we will definitely consider expanding the team further. Joining the curator team is a great way to both contribute to the Haskell ecosystem, and to become more familiar with how things work. You'll also get an opportunity to interact (albeit in brief discussions) with many package maintainers in the Haskell community. If you're interested in applying, please send a message to the Stackage mailing list[3] or, if you prefer applying privately, send me an email and I'll pass the message along to the rest of the team. [1] http://www.snoyman.com/blog/2016/12/call-for-new-stackage-curator [2] https://github.com/fpco/stackage/blob/master/CURATORS.md [3] https://groups.google.com/d/forum/stackage

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happy parser generator - stack space overflow error
by Mageshkumar Kuppusamy 25 Dec '16

25 Dec '16

Hello folks, I am generating a parser for SystemVerilog language using happy parser generator. I have the *.y file which i run using happy as below happy -gca ParSysverilog.y and i get the below error. Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. to increase the stack size and to get more info on the error, i learned that i need to use something like below. happy -RTS -K16384 -sstderr +RTS -gca ParSysverilog.y but i got an error message happy: Most RTS options are disabled. Link with -rtsopts to enable them. does this mean that, i need to recompile happy source code using the "-rtsopts" to use the +RTS...-RTS options ? any recommendations from your experience ? Thank you in advance Magesh

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Re: [Haskell-cafe] happy parser generator - stack space overflow error
by Tobias Dammers 25 Dec '16

25 Dec '16

In my experience, using one of the excellent parser-combinator libraries out there (megaparsec, attoparsec, trifecta) is usually less painful and perfectly adequate. On Dec 25, 2016 7:49 AM, "Mageshkumar Kuppusamy" <magesh.kuppusamy(a)gmail.com> wrote: Hello folks, I am generating a parser for SystemVerilog language using happy parser generator. I have the *.y file which i run using happy as below happy -gca ParSysverilog.y and i get the below error. Stack space overflow: current size 8388608 bytes. Use `+RTS -Ksize -RTS' to increase it. to increase the stack size and to get more info on the error, i learned that i need to use something like below. happy -RTS -K16384 -sstderr +RTS -gca ParSysverilog.y but i got an error message happy: Most RTS options are disabled. Link with -rtsopts to enable them. does this mean that, i need to recompile happy source code using the "-rtsopts" to use the +RTS...-RTS options ? any recommendations from your experience ? Thank you in advance Magesh _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

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ANNOUNCE: Haskell Communities and Activities Report (31st ed., November 2016)
by Mihai Maruseac 24 Dec '16

24 Dec '16

On behalf of all the contributors, we are pleased to announce that the Haskell Communities and Activities Report (31st edition, November 2016) is now available, in PDF and HTML formats: http://haskell.org/communities/11-2016/report.pdf http://haskell.org/communities/11-2016/html/report.html All previous editions of HCAR can be accessed on the wiki at https://wiki.haskell.org/Haskell_Communities_and_Activities_Report Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline) to the call. The editors collect all the contributions into a single report and feed that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ======================================== End of February 2016: target deadline for contributions to the May 2017 edition of the HCAR Report ======================================== Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editors for a simple e-mail reminder in November (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! -- Mihai Maruseac (MM) "If you can't solve a problem, then there's an easier problem you can solve: find it." -- George Polya

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Call for Papers: ICFP 2017
by Lindsey Kuper 23 Dec '16

23 Dec '16

ICFP 2017 The 22nd ACM SIGPLAN International Conference on Functional Programming Oxford, United Kingdom http://icfp17.sigplan.org/ Call for Papers ### Important dates Submissions due: Monday, February 27, Anywhere on Earth https://icfp17.hotcrp.com Author response: Monday, April 17, 2017, 15:00 (UTC) - Thursday, April 20, 2017, 15:00 (UTC) Notification: Monday, 1 May, 2017 Final copy due: Monday, 5 June 2017 Early registration: TBA Conference: Monday, 4 September - Wednesday, 6 September, 2017 ### New this year Those familiar with previous ICFP conferences should be aware of two significant changes that are being introduced in 2017: 1. Papers selected for ICFP 2017 will be published as the ICFP 2017 issue of a new journal, Proceedings of the ACM on Programming Languages (PACMPL), which replaces the previous ICFP conference proceedings. The move to PACMPL will have two noticeable impacts on authors: * A new, two-phase selection and reviewing process that conforms to ACM’s journal reviewing guidelines. * A new, single-column format for submissions. 2. Authors of papers that are conditionally accepted in the first phase of the reviewing process will have the option to submit materials for Artifact Evaluation. Further details on each of these changes are included in the following text. ### Scope ICFP 2017 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, and from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects, concurrency, or parallelism. Topics of interest include (but are not limited to): * *Language Design*: concurrency, parallelism, and distribution; modules; components and composition; metaprogramming; type systems; interoperability; domain-specific languages; and relations to imperative, object-oriented, or logic programming. * *Implementation*: abstract machines; virtual machines; interpretation; compilation; compile-time and run-time optimization; garbage collection and memory management; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components, or low-level machine resources. * *Software-Development Techniques*: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling. * *Foundations*: formal semantics; lambda calculus; rewriting; type theory; monads; continuations; control; state; effects; program verification; dependent types. * *Analysis and Transformation*: control-flow; data-flow; abstract interpretation; partial evaluation; program calculation. * *Applications*: symbolic computing; formal-methods tools; artificial intelligence; systems programming; distributed-systems and web programming; hardware design; databases; XML processing; scientific and numerical computing; graphical user interfaces; multimedia and 3D graphics programming; scripting; system administration; security. * *Education*: teaching introductory programming; parallel programming; mathematical proof; algebra. Submissions will be evaluated according to their relevance, correctness, significance, originality, and clarity. Each submission should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. ICFP 2017 also welcomes submissions in two separate categories — Functional Pearls and Experience Reports — that must be marked as such at the time of submission and that need not report original research results. Detailed guidelines on both categories are given at the end of this call. Please contact the program chair if you have questions or are concerned about the appropriateness of a topic. ### Preparation of submissions **Deadline**: The deadline for submissions is Monday, February 27, 2017, Anywhere on Earth (<https://en.wikipedia.org/wiki/Anywhere_on_Earth>). This deadline will be strictly enforced. **Formatting**: (NOTE: NEW FORMAT REQUIREMENTS FOR ICFP 2017) Submissions must be in PDF format, printable in black and white on US Letter sized paper, and interpretable by common PDF tools. All submissions must adhere to the "ACM Large" template that is available (in both LaTeX and Word formats) from <http://www.acm.org/publications/proceedings-template>. For authors using LaTeX, a lighter-weight package, including only the essential files, is available from <http://sigplan.org/Resources/Author/#acmart-format>. There is a limit of 24 pages for a full paper or 12 pages for an Experience Report; in either case, the bibliography will not be counted against these limits. These page limits have been chosen to allow essentially the same amount of content with the new single-column format as was possible with the two-column format used in past ICFP conferences. Submissions that exceed the page limits or, for other reasons, do not meet the requirements for formatting, will be summarily rejected. **Submission**: Submissions will be accepted at <https://icfp17.hotcrp.com/> (in preparation at the time of writing). Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. **Author Response Period**: Authors will have a 72-hour period, starting at 15:00 UTC on Monday, April 17, 2017, to read reviews and respond to them. **Supplementary Materials**: Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. The material should be uploaded at submission time, as a single pdf or a tarball, not via a URL. This supplementary material may or may not be anonymized; if not anonymized, it will only be revealed to reviewers after they have submitted their review of the paper and learned the identity of the author(s). **Authorship Policies**: All submissions are expected to comply with the ACM Policies for Authorship that are detailed at <https://www.acm.org/publications/authors/information-for-authors>. **Republication Policies**: Each submission must adhere to SIGPLAN's republication policy, as explained on the web at <http://www.sigplan.org/Resources/Policies/Republication>. **Resubmitted Papers**: Authors who submit a revised version of a paper that has previously been rejected by another conference have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the program chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. ### Review Process This section outlines the two-stage process with lightweight double-blind reviewing that will be used to select papers for presentation at ICFP 2017. We anticipate that there will be a need to clarify and expand on this process, and we will maintain a list of frequently asked questions and answers on the conference website to address common concerns. **ICFP 2017 will employ a two-stage review process.** The first stage in the review process will assess submitted papers using the criteria stated above and will allow for feedback and input on initial reviews through the author response period mentioned previously. At the PC meeting, a set of papers will be conditionally accepted and all other papers will be rejected. Authors will be notified of these decisions on May 1, 2017. Authors of conditionally accepted papers will be provided with committee reviews (just as in previous conferences) along with a set of mandatory revisions. After five weeks (June 5, 2017), the authors will provide a second submission. The second and final reviewing phase assesses whether the mandatory revisions have been adequately addressed by the authors and thereby determines the final accept/reject status of the paper. The intent and expectation is that the mandatory revisions can be addressed within five weeks and hence that conditionally accepted papers will in general be accepted in the second phase. The second submission should clearly identify how the mandatory revisions were addressed. To that end, the second submission must be accompanied by a cover letter mapping each mandatory revision request to specific parts of the paper. The cover letter will facilitate a quick second review, allowing for confirmation of final acceptance within two weeks. Conversely, the absence of a cover letter will be grounds for the paper’s rejection. This process is intended as a refinement of the review process that has been used in previous ICFP conferences. By incorporating a second stage, the process will conform to ACM’s journal reviewing guidelines for PACMPL. **ICFP 2017 will employ a lightweight double-blind reviewing process.** To facilitate this, submitted papers must adhere to two rules: 1. **author names and institutions must be omitted**, and 2. **references to authors' own related work should be in the third person** (e.g., not "We build on our previous work ..." but rather "We build on the work of ..."). The purpose of this process is to help the PC and external reviewers come to an initial judgement about the paper without bias, not to make it impossible for them to discover the authors if they were to try. Nothing should be done in the name of anonymity that weakens the submission or makes the job of reviewing the paper more difficult (e.g., important background references should not be omitted or anonymized). In addition, authors should feel free to disseminate their ideas or draft versions of their paper as they normally would. For instance, authors may post drafts of their papers on the web or give talks on their research ideas. ### Information for Authors of Accepted Papers * As a condition of acceptance, final versions of all papers must adhere to the new ACM Large format. The page limits for final versions of papers will be increased to ensure that authors have space to respond to reviewer comments and mandatory revisions. * Authors of accepted submissions will be required to agree to one of the three ACM licensing options: copyright transfer to ACM; retaining copyright but granting ACM exclusive publication rights; or open access on payment of a fee. Further information about ACM author rights is available from <http://authors.acm.org>. * At least one author of each accepted submissions will be expected to attend and present their paper at the conference. The schedule for presentations will be determined and shared with authors after the full program has been selected. Presentations will be videotaped and released online if the presenter consents. * We intend that the proceedings will be freely available for download from the ACM Digital Library in perpetuity via the OpenTOC mechanism. * ACM Author-Izer is a unique service that enables ACM authors to generate and post links on either their home page or institutional repository for visitors to download the definitive version of their articles from the ACM Digital Library at no charge. Downloads through Author-Izer links are captured in official ACM statistics, improving the accuracy of usage and impact measurements. Consistently linking to the definitive version of an ACM article should reduce user confusion over article versioning. After an article has been published and assigned to the appropriate ACM Author Profile pages, authors should visit <http://www.acm.org/publications/acm-author-izer-service> to learn how to create links for free downloads from the ACM DL. * The official publication date is the date the proceedings are made available in the ACM Digital Library. This date may be up to *two weeks prior* to the first day of the conference. The official publication date affects the deadline for any patent filings related to published work. ### Artifact Evaluation Authors of papers that are conditionally accepted in the first phase of the review process will be encouraged (but not required) to submit supporting materials for Artifact Evaluation. These items will then be reviewed by a committee, separate from the program committee, whose task is to assess how the artifacts support the work described in the associated paper. Papers that go through the Artifact Evaluation process successfully will receive a seal of approval printed on the papers themselves. Authors of accepted papers will be encouraged to make the supporting materials publicly available upon publication of the proceedings, for example, by including them as "source materials" in the ACM Digital Library. An additional seal will mark papers whose artifacts are made available, as outlined in the ACM guidelines for artifact badging. Participation in Artifact Evaluation is voluntary and will not influence the final decision regarding paper acceptance. Further information about the motivations and expectations for Artifact Evaluation can be found at <http://icfp17.sigplan.org/track/icfp-2017-Artifacts>. ### Special categories of papers In addition to research papers, ICFP solicits two kinds of papers that do not require original research contributions: Functional Pearls, which are full papers, and Experience Reports, which are limited to half the length of a full paper. Authors submitting such papers should consider the following guidelines. #### Functional Pearls A Functional Pearl is an elegant essay about something related to functional programming. Examples include, but are not limited to: * a new and thought-provoking way of looking at an old idea * an instructive example of program calculation or proof * a nifty presentation of an old or new data structure * an interesting application of functional programming techniques * a novel use or exposition of functional programming in the classroom While pearls often demonstrate an idea through the development of a short program, there is no requirement or expectation that they do so. Thus, they encompass the notions of theoretical and educational pearls. Functional Pearls are valued as highly and judged as rigorously as ordinary papers, but using somewhat different criteria. In particular, a pearl is not required to report original research, but, it should be concise, instructive, and entertaining. A pearl is likely to be rejected if its readers get bored, if the material gets too complicated, if too much specialized knowledge is needed, or if the writing is inelegant. The key to writing a good pearl is polishing. A submission that is intended to be treated as a pearl must be marked as such on the submission web page, and should contain the words "Functional Pearl" somewhere in its title or subtitle. These steps will alert reviewers to use the appropriate evaluation criteria. Pearls will be combined with ordinary papers, however, for the purpose of computing the conference's acceptance rate. #### Experience Reports The purpose of an Experience Report is to help create a body of published, refereed, citable evidence that functional programming really works — or to describe what obstacles prevent it from working. Possible topics for an Experience Report include, but are not limited to: * insights gained from real-world projects using functional programming * comparison of functional programming with conventional programming in the context of an industrial project or a university curriculum * project-management, business, or legal issues encountered when using functional programming in a real-world project * curricular issues encountered when using functional programming in education * real-world constraints that created special challenges for an implementation of a functional language or for functional programming in general An Experience Report is distinguished from a normal ICFP paper by its title, by its length, and by the criteria used to evaluate it. * Both in the proceedings and in any citations, the title of each accepted Experience Report must begin with the words "Experience Report" followed by a colon. The acceptance rate for Experience Reports will be computed and reported separately from the rate for ordinary papers. * Experience Report submissions can be at most 12 pages long, excluding bibliography. * Each accepted Experience Report will be presented at the conference, but depending on the number of Experience Reports and regular papers accepted, authors of Experience reports may be asked to give shorter talks. * Because the purpose of Experience Reports is to enable our community to accumulate a body of evidence about the efficacy of functional programming, an acceptable Experience Report need not add to the body of knowledge of the functional-programming community by presenting novel results or conclusions. It is sufficient if the Report states a clear thesis and provides supporting evidence. The thesis must be relevant to ICFP, but it need not be novel. The program committee will accept or reject Experience Reports based on whether they judge the evidence to be convincing. Anecdotal evidence will be acceptable provided it is well argued and the author explains what efforts were made to gather as much evidence as possible. Typically, more convincing evidence is obtained from papers which show how functional programming was used than from papers which only say that functional programming was used. The most convincing evidence often includes comparisons of situations before and after the introduction or discontinuation of functional programming. Evidence drawn from a single person's experience may be sufficient, but more weight will be given to evidence drawn from the experience of groups of people. An Experience Report should be short and to the point: it should make a claim about how well functional programming worked on a particular project and why, and produce evidence to substantiate this claim. If functional programming worked in this case in the same ways it has worked for others, the paper need only summarize the results — the main part of the paper should discuss how well it worked and in what context. Most readers will not want to know all the details of the project and its implementation, but the paper should characterize the project and its context well enough so that readers can judge to what degree this experience is relevant to their own projects. The paper should take care to highlight any unusual aspects of the project. Specifics about the project are more valuable than generalities about functional programming; for example, it is more valuable to say that the team delivered its software a month ahead of schedule than it is to say that functional programming made the team more productive. If the paper not only describes experience but also presents new technical results, or if the experience refutes cherished beliefs of the functional-programming community, it may be better off submitted it as a full paper, which will be judged by the usual criteria of novelty, originality, and relevance. The program chair will be happy to advise on any concerns about which category to submit to. ### Organizers General Chair: Jeremy Gibbons (University of Oxford, UK) Program Chair: Mark Jones (Portland State University, USA) Artifact Evaluation Chair: Ryan R. Newton (Indiana University, USA) Industrial Relations Chair: Ryan Trinkle (Obsidian Systems LLC, USA) Programming Contest Organiser: Sam Lindley (University of Edinburgh, UK) Publicity and Web Chair: Lindsey Kuper (Intel Labs, USA) Student Research Competition Chair: Ilya Sergey (University College London, UK) Video Chair: Jose Calderon (Galois, Inc., USA) Workshops Co-Chair: Andres Löh (Well-Typed LLP) Workshops Co-Chair: David Christiansen (Indiana University, USA) Program Committee: Bob Atkey (University of Strathclyde, Scotland) Adam Chlipala (MIT, USA) Dominique Devriese (KU Leuven, Belgium) Martin Erwig (Oregon State, USA) Matthew Flatt (University of Utah, USA) Ronald Garcia (University of British Columbia, Canada) Kathryn Gray (University of Cambridge, England) John Hughes (Chalmers University and Quvik, Sweden) Chung-Kil Hur (Seoul National University, Korea) Graham Hutton (University of Nottingham, England) Alan Jeffrey (Mozilla Research, USA) Ranjit Jhala (University of California, San Diego, USA) Shin-ya Katsumata (Kyoto University, Japan) Lindsey Kuper (Intel Labs, USA) Dan Licata (Wesleyan University, USA) Ben Lippmeier (Digital Asset, Australia) Gabriel Scherer (Northeastern University, USA) Alexandra Silva (University College London, England) Nikhil Swamy (Microsoft Research, USA) Sam Tobin-Hochstadt (Indiana University, USA) Nicolas Wu (University of Bristol, England) Beta Ziliani (CONICET and FAMAF, Universidad Nacional de Córdoba, Argentina)

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Fwd: Datomic-like db for Haskell?
by Ovidiu Deac 23 Dec '16

23 Dec '16

> > * Would using a snapshot-based revision control system like Git be an > option? If yes, you could use the [filestore] library. > It's not exactly what I had in mind but I'll think about it. > > * Another option is to run an insertion-only relational model on > really any database system you want like PostgreSQL. There is > nothing about preserving history that needs special handling to be > efficient. > I assume that some sort of structural sharing is needed once the collections grow above a certain size. Also some support for caching would be nice. > * Yet another option is to model your application state with history > and use [acid-state]. However, acid-state only makes an in-memory > Haskell value (the "database") persistent with ACID guarantees. If > you mostly work with the current state, keeping the whole history in > memory all the time would be a waste. Therefore this option may be > less useful. > The database will probably grow bigger than the memory so this is not an option. ...and thanks for the pointers

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Lenses: Changing/creating values deep inside JSON or HashMap
by Jan von Löwenstein 23 Dec '16

23 Dec '16

Hi, I want to have code that produces the following result no matter if input A or B was given: Result: { "outer" : { "inner" : "new-value" } } A: { "outer" : { "inner" : "old-value" } } B: {} `json & key "outer"._Object.key "inner" .~ "new-value"` didn't work. Is what I want even possible with lenses? Best Jan

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Datomic-like db for Haskell?
by Ovidiu Deac 23 Dec '16

23 Dec '16

Is there any package in Haskell that provides something similar to Datomic http://www.datomic.com/? Basically what I am looking for is a database which could keep all the versions of my data in an efficient way, the same way the persistent data structures do. Ideally it should be implemented over some scalable storage. I looked at Datomic itself but I couldn't find a Haskell client library. The only way to connect to it from a Haskell application is through the REST server which they have just deprecated ( http://docs.datomic.com/rest.html) Thanks!

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Work on mail.haskell.org beginning, please report any problems
by John Wiegley 23 Dec '16

23 Dec '16

Hello Haskellers, Beginning today, I am upgrading our Postfix installation on mail.haskell.org, and introducing some new options to reduce the amount of spam that hits our mailman server. If you experience delivery problems, or any bounced mail, please send a copy of the full bounce message to my address: jwiegley(a)gmail.com. I'll be making more changes gradually over the next few days, and watching the mail logs, but it's possible that mail accepted before will suddenly start getting rejected, depending on how well-behaved your sending mail server is. Activities planned for this Christmas break are: - [x] Upgrade Postfix to 2.11 - [X] Enable postscreen for pre-queue RBL filtering - [ ] DKIM sign messages sent from mailman - [ ] Implement DMARC policy (i.e., reject incoming messages improperly DKIM signed, or failing SPF check) - [ ] Prevent mail being spoofed from haskell.org addresses - [ ] Tighten sender and recipient restrictions - [ ] Re-assess inbound and outbound rate limits - [ ] Use SpamAssassin for post-queue filtering - [ ] If helpful, enable deep protocol pre-filtering - [ ] Document all the above, so others can help with e-mail admin Thank you, John Wiegley Haskell.org, infrastructure team

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