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Order of Map.fromListWith
by Niklas Hambüchen 04 Mar '16

04 Mar '16

Does anybody know why for fromListWith, the arguments to the combining function seem flipped? > import Data.Map > fromListWith (++) [('a',[1]),('a',[2])] fromList [('a',[2,1])] I often use it to group things by some key, e.g. postsByUserId :: Map Int [Int] postsByUserId = fromListWith (++) [ (userId, [postId]) | (userId, postId) <- posts ] and regularly get tricked by the postIds being reversed in the result. This is especially unintuitive to me since: > foldl (++) [] [[1],[2]] [1,2] > foldr (++) [] [[1],[2]] [1,2] Any ideas?

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Local mirrors of hackage
by Victor Miller 04 Mar '16

04 Mar '16

I have a computer that I work on which isn't directly connected to the internet, that I want to use Haskell on. In order to do that I want a local version of hackage. I was previously able to do this using mirror_hackage.py, but since hackage 2 came around this no longer works. Doing this would involve running something on a computer that *is* attached to the internet, and then transferring a bunch of files over to the other computer. Can someone point me to a recipe for doing this? Victor

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ICFP 2016 Final Call for Papers
by Lindsey Kuper 03 Mar '16

03 Mar '16

ICFP 2016 The 21st ACM SIGPLAN International Conference on Functional Programming http://conf.researchr.org/home/icfp-2016 Final Call for Papers Important dates --------------- Submissions due: Wednesday, March 16 2016, 15:00 (UTC) https://icfp2016.hotcrp.com (now open) Author response: Monday, 2 May, 2016, 15:00 (UTC) - Thursday, 5 May, 2016, 15:00 (UTC) Notification: Friday, 20 May, 2016 Final copy due: TBA Early registration: TBA Conference: Monday, 19 September - Wednesday, 21 September, 2016 Please note ----------- For the sake of lightweight double-blind reviewing, the submission procedure may take a little more time than in previous ICFPs; we recommend that you register your submission as early as possible (you can update your paper until the deadline). Scope ----- ICFP 2016 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. - Functional Pearls: elegant, instructive, and fun essays on functional programming. - Experience Reports: short papers that provide evidence that functional programming really works or describe obstacles that have kept it from working. If you are concerned about the appropriateness of some topic, do not hesitate to contact the program chair. Abbreviated instructions for authors ------------------------------------ - By Wednesday, March 16 2016, 15:00 (UTC), submit a full paper of at most 12 pages (6 pages for an Experience Report), in standard SIGPLAN conference format, including figures but ***excluding bibliography***. The deadlines will be strictly enforced and papers exceeding the page limits will be summarily rejected. ***ICFP 2016 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. We have put together a document answering frequently asked questions that should address many common concerns: http://conf.researchr.org/track/icfp-2016/icfp-2016-papers#Submission-and-R… (last updated February 8, 2016). - 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 your paper and learned your identity. - Each submission must adhere to SIGPLAN's republication policy, as explained on the web at: http://www.sigplan.org/Resources/Policies/Republication - Authors of resubmitted (but previously rejected) papers 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. Overall, a submission will be evaluated according to its relevance, correctness, significance, originality, and clarity. It 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. Functional Pearls and Experience Reports are separate categories of papers that need not report original research results and must be marked as such at the time of submission. Detailed guidelines on both categories are given below. Presentations will be videotaped and released online if the presenter consents. The proceedings will be freely available for download from the ACM Digital Library from at least one week before the start of the conference until two weeks after the conference. Formatting: Submissions must be in PDF format printable in black and white on US Letter sized paper and interpretable by Ghostscript. Papers must adhere to the standard SIGPLAN conference format: two columns, nine-point font on a ten-point baseline, with columns 20pc (3.33in) wide and 54pc (9in) tall, with a column gutter of 2pc (0.33in). A suitable document template for LaTeX is available at http://www.sigplan.org/Resources/Author/ Submission: Submissions will be accepted at https://icfp2016.hotcrp.com . Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Author response: Authors will have a 72-hour period, starting at 15:00 UTC on Monday, 2 May, 2016, to read reviews and respond to them. 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 the definitive version of ACM article should reduce user confusion over article versioning. After your article has been published and assigned to your ACM Author Profile page, please visit http://www.acm.org/publications/acm-author-izer-service to learn how to create your links for free downloads from the ACM DL. AUTHORS TAKE NOTE: 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 your conference. The official publication date affects the deadline for any patent filings related to published work. 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 six pages. Authors submitting such papers may wish to consider the following advice. 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. Your pearl is likely to be rejected if your 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 you wish to have 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. - An Experience Report is at most six pages long. 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: make a claim about how well functional programming worked on your project and why, and produce evidence to substantiate your claim. If functional programming worked for you in the same ways it has worked for others, you need only to summarize the results?the main part of your paper should discuss how well it worked and in what context. Most readers will not want to know all the details of your project and its implementation, but please characterize your project and its context well enough so that readers can judge to what degree your experience is relevant to their own projects. Be especially careful to highlight any unusual aspects of your project. Also keep in mind that specifics about your project are more valuable than generalities about functional programming; for example, it is more valuable to say that your team delivered its software a month ahead of schedule than it is to say that functional programming made your team more productive. If your paper not only describes experience but also presents new technical results, or if your experience refutes cherished beliefs of the functional-programming community, you may be better off submitting it as a full paper, which will be judged by the usual criteria of novelty, originality, and relevance. If you are unsure in which category to submit, the program chair will be happy to help you decide. Organizers ---------- General Co-Chairs: Jacques Garrigue (Nagoya University) Gabriele Keller (University of New South Wales) Program Chair: Eijiro Sumii (Tohoku University) Program Committee: Koen Claessen (Chalmers University of Technology) Joshua Dunfield (University of British Columbia, Canada) Matthew Fluet (Rochester Institute of Technology) Nate Foster (Cornell University) Dan Grossman (University of Washington, USA) Jurriaan Hage (Utrecht University) Roman Leshchinskiy (Standard Chartered Bank) Keisuke Nakano (The University of Electro-Communications) Aleksandar Nanevski (IMDEA Software Institute) Scott Owens (University of Kent) Sungwoo Park (Pohang University of Science and Technology) Amr Sabry (Indiana University) Tom Schrijvers (KU Leuven) Olin Shivers (Northeastern University) Walid Taha (Halmstad University) Dimitrios Vytiniotis (Microsoft Research, Cambridge) David Walker (Princeton University) Nobuko Yoshida (Imperial College London, UK) External Review Committee: See http://conf.researchr.org/committee/icfp-2016/icfp-2016-papers-external-rev… .

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Take over netlink-hs
by Markus Ongyerth 02 Mar '16

02 Mar '16

Hi, I want to take over the netlink package on hackage [1]. In accordance to [2] I want to announce that publicly on this list. I have tried to contact the auther in october 2015, and talked about it on the #haskell irc channel. I was able to reach the current maintainer, he told me that he forgot about it and doesn't know his hackage password anymore. Davean (on IRC) offerden to give me maintainer rights after checking back with Max himself. I didn't hear anything after that, neither have I made any effort in this matter since then. ongy [1] https://hackage.haskell.org/package/netlink [2] https://wiki.haskell.org/Taking_over_a_package

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How do I sort items in a wxhaskell listCtrl?
by Tilmann 02 Mar '16

02 Mar '16

Hi list, I couldn't find any clues googling and turn to you in the hope that someone might point me in the right direction: I found the function |listCtrlSortItems2| with type |ListCtrl a -> Closure b -> IO Bool| and |closureCreate| (which type is a bit involved..), but I have no idea how to use them.. In the end, I would like to have a listCtrl where clicking on column headers will sort the items and maybe even indicating sorting order with a little arrow. Any help is really appreciated, Tilmann

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Haskell 2016: Call for Papers
by Geoffrey Mainland 02 Mar '16

02 Mar '16

======================================================================== ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2016 Nara, Japan, 22-23 September 2015, directly after ICFP http://www.haskell.org/haskell-symposium/2016 ======================================================================== ** The Haskell Symposium has an early track this year ** ** See the Submission Timetable for details. ** The ACM SIGPLAN Haskell Symposium 2016 will be co-located with the International Conference on Functional Programming (ICFP 2016) in Vancouver, Canada. The Haskell Symposium aims to present original research on Haskell, discuss practical experience and future development of the language, and to promote other forms of denotative programming. Topics of interest include: * Language Design, with a focus on possible extensions and modifications of Haskell as well as critical discussions of the status quo; * Theory, such as formal semantics of the present language or future extensions, type systems, effects, metatheory, and foundations for program analysis and transformation; * Implementations, including program analysis and transformation, static and dynamic compilation for sequential, parallel, and distributed architectures, memory management, as well as foreign function and component interfaces; * Libraries, that demonstrate new ideas or techniques for functional programming in Haskell; * Tools, such as profilers, tracers, debuggers, preprocessors, and testing tools; * Applications, to scientific and symbolic computing, databases, multimedia, telecommunication, the web, and so forth; * Functional Pearls, being elegant and instructive programming examples; * Experience Reports, to document general practice and experience in education, industry, or other contexts. Papers in the latter three categories need not necessarily report original academic research results. For example, they may instead report reusable programming idioms, elegant ways to approach a problem, or practical experience that will be useful to other users, implementors, or researchers. The key criterion for such a paper is that it makes a contribution from which other Haskellers can benefit. It is not enough simply to describe a standard solution to a standard programming problem, or report on experience where you used Haskell in the standard way and achieved the result you were expecting. More advice is available via the Haskell wiki: (http://wiki.haskell.org/HaskellSymposium/ExperienceReports) Regular papers should explain their research contributions in both general and technical terms, identifying what has been accomplished, explaining why it is significant, and relating it to previous work, and to other languages where appropriate. In addition, we solicit proposals for: * System Demonstrations, based on running software rather than novel research results. These proposals should summarize the system capabilities that would be demonstrated. The proposals will be judged on whether the ensuing session is likely to be important and interesting to the Haskell community at large, whether on grounds academic or industrial, theoretical or practical, technical, social or artistic. Please contact the program chair with any questions about the relevance of a proposal. Travel Support: =============== Student attendees with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC program, see its web page (http://pac.sigplan.org) Proceedings: ============ Accepted papers will be included in the ACM Digital Library. Authors must grant ACM publication rights upon acceptance (http://authors.acm.org/main.html) Authors are encouraged to publish auxiliary material with their paper (source code, test data, etc.); they retain copyright of auxiliary material. Accepted proposals for system demonstrations will be posted on the symposium website but not formally published in the proceedings. All accepted papers and proposals will be posted on the conference website one week before the meeting. Publication date: The official publication date of accepted papers 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. Submission Details: =================== Submitted papers should be in portable document format (PDF), formatted using the ACM SIGPLAN style guidelines (http://www.acm.org/sigs/sigplan/authorInformation.htm) The text should be in a 9-point font in two columns. The length is restricted to 12 pages, except for "Experience Report" papers, which are restricted to 6 pages. Papers need not fill the page limit---for example, a Functional Pearl may be much shorter than 12 pages. Each paper submission must adhere to SIGPLAN's republication policy, as explained on the web. Demo proposals are limited to 2-page abstracts, in the same ACM format as papers. "Functional Pearls", "Experience Reports", and "Demo Proposals" should be marked as such with those words in the title at time of submission. The paper submission deadline and length limitations are firm. There will be no extensions, and papers violating the length limitations will be summarily rejected. A link to the paper submission system will appear on the Haskell Symposium web site closer to the submission deadline. Submission Timetable: ===================== Early Track Regular Track System Demos ---------------- ------------------- --------------- 1st April Paper Submission 20th May Notification 6th June Abstract Submission 10th June Paper Submission 17th June Resubmission Demo Submission 8th July Notification Notification Notification 31st July Camera ready due Camera ready due Deadlines stated are valid anywhere on earth. The Haskell Symposium uses a two-track submission process so that some papers can gain early feedback. Papers can be submitted to the early track on 1st April. On 20th May, strong papers are accepted outright, and the others will be given their reviews and invited to resubmit. On 17th June, early track papers may be resubmitted and are sent back to the same reviewers. The Haskell Symposium regular track operates as in previous years. Papers accepted via the early and regular tracks are considered of equal value and will not be distinguished in the proceedings. Although all papers may be submitted to the early track, authors of functional pearls and experience reports are particularly encouraged to use this mechanism. The success of these papers depends heavily on the way they are presented, and submitting early will give the program committee a chance to provide feedback and help draw out the key ideas. Program Committee: =================== James Cheney University of Edinburgh Iavor Diatchki Galois David Duke University of Leeds Richard Eisenberg University of Pennsylvania Ken Friis Larsen University of Copenhagen Andy Gill University of Kansas Zhenjiang Hu National Institute of Informatics Ranjit Jhala UC San Diego Yukiyoshi Kameyama University of Tsukuba Geoffrey Mainland (chair) Drexel University Mary Sheeran Chalmers University of Technology David Terei Stanford Niki Vazou UC San Diego Dimitrios Vytiniotis Microsoft Research =====================================================================

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[TFP 2016] 2nd call for papers
by Peter Achten 01 Mar '16

01 Mar '16

----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2016 =========== 17th Symposium on Trends in Functional Programming June 8-10, 2016 University of Maryland, College Park Near Washington, DC http://tfp2016.org/ The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. TFP 2016 will be the main event of a pair of functional programming events. TFP 2016 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on June 7nd. == INVITED SPEAKERS == TFP 2016 is pleased to announce keynote talks by the following two invited speakers: * Ronald Garcia, University of British Columbia * Steve Zdancewic, University of Pennsylvania == HISTORY == The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * Soesterberg (The Netherlands) in 2014; * and Inria Sophia-Antipolis (France) in 2015. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2016 program chair, David Van Horn. == BEST PAPER AWARDS == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == SPONSORS == TFP is financially supported by CyberPoint, Galois, Trail of Bits, and the University of Maryland Computer Science Department. == PAPER SUBMISSIONS == Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which ALL authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. Papers must be submitted at: https://easychair.org/conferences/?conf=tfp2016 Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site: http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0 == IMPORTANT DATES == Submission of draft papers: April 8, 2016 Notification: April 15, 2016 Registration: May 13, 2016 TFP Symposium: June 8-10, 2016 Student papers feedback: June 14, 2016 Submission for formal review: July 14, 2016 Notification of acceptance: September 14, 2016 Camera ready paper: October 14, 2016 == PROGRAM COMMITTEE == Amal Ahmed Northeastern University (US) Nada Amin École Polytechnique Fédérale de Lausanne (CH) Kenichi Asai Ochanomizu University (JP) Malgorzata Biernacka University of Wroclaw (PL) Laura Castro University of A Coruña (ES) Ravi Chugh University of Chicago (US) Silvia Ghilezan University of Novi Sad (SR) Clemens Grelck University of Amsterdam (NL) John Hughes Chalmers University of Technology (SE) Suresh Jagannathan Purdue University (US) Pieter Koopman Radboud University Nijmegen (NL) Geoffrey Mainland Drexel University (US) Chris Martens University of California, Santa Cruz (US) Jay McCarthy University of Massachusetts, Lowell (US) Heather Miller École Polytechnique Fédérale de Lausanne (CH) Manuel Serrano INRIA, Sophia-Antipolis (FR) Scott Smith Johns Hopkins University (US) Éric Tanter University of Chile (CL) David Van Horn (Chair) University of Maryland (US) Niki Vazou University of California, San Diego (US) Stephanie Weirich University of Pennsylvania (US)

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Re: [Haskell-cafe] Compile times and separate compilation
by Johannes Waldmann 01 Mar '16

01 Mar '16

> I presume you are using the -j switch. Does it really help? I recently found that for travis builds, it is used by default (first surprise) but it's faster when it's turned off (second surprise). https://ghc.haskell.org/trac/ghc/ticket/10818#comment:15 - J.

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Haskell Summer of Code
by Edward Kmett 01 Mar '16

01 Mar '16

I'm sorry to announce that this year haskell.org was not accepted for the 2016 Google Summer of Code. There has been a lot of turnover over the last 3 years as they have rotated in and out new organizations, including many that have been in the program as long as us, so while this isn't entirely unexpected, it is disheartening. As this comes on the tail of our most successful year in the program, the news was particularly devastating to all involved. We do not expect this to be a permanent condition. Many organizations rotate back in and out of the Summer of Code each year. Operationally, this raises two main concerns: The first is that there will be a rather sharp dip in income for the next year for haskell.org. Last year's GSoC accounted for $9500 worth of income towards managing servers and the like, but we will not receive such a booster shot this year. The second is that we absolutely do not want the infrastructure we have in place around the Summer of Code to fall away. We had 50 mentors register last year! To address both of these concerns, we are exploring running our own self-funded *Haskell Summer of Code *this year*. *In December, we incorporated haskell.org as a 501(c)(3) non-profit. This now enables us to pay for work directly. We should be able to fund at least one slot out of pocket from existing haskell.org funds and fund additional slots with donations. https://wiki.haskell.org/Donate_to_Haskell.org More information will be forthcoming as we work out the details. Please feel free to contact me if you think you can help or if you have any questions or concerns. -Edward Kmett

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Infer Nat type from Integer argument
by Jake 01 Mar '16

01 Mar '16

{-# LANGUAGE DataKinds, KindSignatures, ScopedTypeVariables, GADTs, AllowAmbiguousTypes #-} import GHC.TypeLits import Data.Proxy import Data.Type.Equality data NatString (n :: Nat) = NatString String deriving Show showNS :: KnownNat n => NatString n -> (String, Integer) showNS b@(NatString s) = (s, natVal b) In this example, we use NatString like this: > showNS (NatString "hey" :: NatString 4) -- ("hey", 4) We can then dynamically make NatStrings from Integers. For example, we can read an Integer from stdin and use it to create a NatString main :: IO () main = do i <- readLn case someNatVal i of Just (SomeNat (p :: Proxy n)) -> let ns :: NatString n ns = NatString "hello!" in print $ showNS NatString However, if I have trouble when I try to refactor out the middle part to create a function with type forall n. KnownNat n => Integer -> Bar n. I use sameNat to convince the compiler that the Nat we get from the Integer is the same type as the the type n of the output. fromN :: forall n. KnownNat n => Integer -> NatString n fromN i = case someNatVal i of Just (SomeNat p) -> case sameNat p (Proxy :: Proxy n) of Just (Refl) -> let ns :: NatString n ns = NatString "hello!" in ns This compiles, but if you try and use it the compiler complains. > showNS (fromN 3) -- No instance for (KnownNat n0) arising from a use of ‘showNS’ If we manually add the type annotation, everything is fine, but that kind of defeats the entire purpose. > showNS (fromN 3 :: NatString 3) -- ("hello!",3) Strangely enough, when the NatString is immediately consumed instead of being returned, the compiler does its job and infers the correct type. showFromN :: Integer -> (String, Integer) showFromN i = case someNatVal i of Just (SomeNat (p :: Proxy n)) -> let ns :: NatString n ns = NatString "hello!" in showNS ns > showFromN 3 -- ("hello!", 3) Clearly the intermediate value of ns inside of showFromN has a type NatString 3 because showNS is using that fact. How can I make the compiler infer that fromN 3 :: NatString 3 separately?

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