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CFP: Functional High Performance Computing 2016
by David Duke 03 Apr '16

03 Apr '16

====================================================================== CALL FOR PAPERS FHPC 2016 The 5th ACM SIGPLAN Workshop on Functional High-Performance Computing Nara, Japan September 22, 2016 https://sites.google.com/site/fhpcworkshops/ Co-located with the International Conference on Functional Programming (ICFP 2016) Submission Deadline: Friday, 10 June, 2016 (anywhere on earth) ====================================================================== The FHPC workshop aims at bringing together researchers exploring uses of functional (or more generally, declarative or high-level) programming technology in application domains where high performance is essential. The aim of the meeting is to enable sharing of results, experiences, and novel ideas about how high-level, declarative specifications of computationally challenging problems can serve as maintainable and portable code that approaches (or even exceeds) the performance of machine-oriented imperative implementations. All aspects of performance critical programming and parallel programming are in-scope for the workshop, irrespective of hardware target. This includes both traditional large-scale scientific computing (HPC), as well as work targeting single node systems with SMPs, GPUs, FPGAs, or embedded processors. It is becoming apparent that radically new and well founded methodologies for programming such systems are required to address their inherent complexity and to reconcile execution performance with programming productivity. Experience reports are also welcome. Proceedings: ============ FHPC 2016 seeks to encourage a range of submissions, focussing on work in progress and facilitating early exchange of ideas and open discussion on innovative and/or emerging results. To this end submissions should take the form of short (maximum 6 page) papers. Accepted papers will be published by the ACM and will appear in the ACM Digital Library. * Submissions due: Friday, 10 June, 2016 (anywhere on earth) * Author notification: Friday, 8 July, 2016 * Final copy due: Sunday, 31 July, 2016 Submitted papers must be in portable document format (PDF), formatted according to the ACM SIGPLAN style guidelines (2 column, 9pt format). See http://www.sigplan.org/authorInformation.htm for more information and style files. Papers should be no longer than 6 pages. Contributions to FHPC 2016 should be submitted via Easychair, at the following URL: * https://www.easychair.org/conferences/?conf=fhpc16 The FHPC workshops adhere to the ACM SIGPLAN policies regarding programme committee contributions and republication. Any paper submitted must adhere to ACM SIGPLAN's republication policy. PC member submissions are welcome, but will be reviewed to a higher standard. http://www.sigplan.org/Resources/Policies/Review http://www.sigplan.org/Resources/Policies/Republication 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 programme, see its web page (http://www.sigplan.org/PAC.htm) Programme Committee: ==================== David Duke (co-chair) University of Leeds, UK Yukiyoshi Kameyama (co-chair) University of Tsukuba, Japan Baris Aktemur Özyeğin University, Turkey Marco Aldinucci University of Torino, Italy Jost Berthold Commonwealth Bank, Australia Kei Davis Los Alamos National Laboratory, USA Kento Emoto Kyushu Institute of Technology, Japan Zhenjiang Hu National Institute of Informatics, Japan Ben Lippmeier University of New South Wales, Australia Rita Loogen University of Marburg, Germany Geoffrey Mainland Drexel University, USA Mike Rainey INRIA, France Mary Sheeran Chalmers University of Technology, Sweden Satnam Singh Facebook, UK

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ANNOUNCE: fadno-braids 0.0.2
by Stuart Popejoy 03 Apr '16

03 Apr '16

Braids represented as Haskell types with support for generation and transformations. Artin generators, Birman-Ko-Lee band generators, isotopy/Reidemeister moves, rendering via Diagrams. https://hackage.haskell.org/package/fadno-braids-0.0.2 Thanks, Stuart

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Fastest way to calculate all the ways to interleave two lists
by David Feuer 03 Apr '16

03 Apr '16

I ran into a fun question today: http://stackoverflow.com/q/36342967/1477667 Specifically, it asks how to find all ways to interleave lists so that the order of elements within each list is preserved. The most efficient way I found is copied below. It's nicely lazy, and avoids left-nested appends. Unfortunately, it's pretty seriously ugly. Does anyone have any idea of a way to do this that's both efficient and elegant? {-# LANGUAGE BangPatterns #-} import Data.Monoid import Data.Foldable (toList) import Data.Sequence (Seq, (|>)) -- Find all ways to interleave two lists interleave2 :: [a] -> [a] -> [[a]] interleave2 xs ys = interleave2' mempty xs ys [] -- Find all ways to interleave two lists, adding the -- given prefix to each result and continuing with -- a given list to append interleave2' :: Seq a -> [a] -> [a] -> [[a]] -> [[a]] interleave2' !prefix xs ys rest = (toList prefix ++ xs ++ ys) : interleave2'' prefix xs ys rest -- Find all ways to interleave two lists except for -- the trivial case of just appending them. Glom -- the results onto the given list. interleave2'' :: Seq a -> [a] -> [a] -> [[a]] -> [[a]] interleave2'' !prefix [] _ = id interleave2'' !prefix _ [] = id interleave2'' !prefix xs@(x : xs') ys@(y : ys') = interleave2' (prefix |> y) xs ys' . interleave2'' (prefix |> x) xs' ys -- What the question poser wanted; I don't *think* there's -- anything terribly interesting to do here. interleavings :: [[a]] -> [[a]] interleavings = foldr (concatMap . interleave2) [[]] Thanks, David

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Month in Haskell Mode March 2016
by Gracjan Polak 01 Apr '16

01 Apr '16

Welcome Haskell Mode users, Haskell Mode progress report for March 2016. For previous issue see February 2016 <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-February…>. Reddit discussion <https://www.reddit.com/r/haskell/comments/4cx7hc/month_in_haskell_mode_marc…> . <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-March-20…>What is Haskell Mode? Haskell Mode is an umbrella project for multiple Emacs tools for efficient Haskell development. Haskell Mode is an open source project developed by a group of volunteers constantly looking for contributions. For more information how to help see https://github.com/haskell/haskell-mode. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-March-20…>Important developments We have noticed that haskell-mode project on Github is steadily growing in popularity and that is clearly visible on historical growth graph: [image: History of stars on github leading to the number 700] So star us on Github, follow us on Twitter: @HaskellMode <https://twitter.com/HaskellMode>. <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-March-20…>Issues closed in February - Implement REPL RET behaviour on previous prompts #30 <https://github.com/haskell/haskell-mode/issues/30> - Disable Indentation #90 <https://github.com/haskell/haskell-mode/issues/90> - Del/Backspace do not delete text selection in literate mode outside bird lines #379 <https://github.com/haskell/haskell-mode/issues/379> - haskell-mode-jump-to-def-or-tag Requires a running session #650 <https://github.com/haskell/haskell-mode/issues/650> - haskell-indentation-mode does not bind DEL #721 <https://github.com/haskell/haskell-mode/issues/721> - REPL does not work properly until load or reload file second time #765 <https://github.com/haskell/haskell-mode/issues/765> - Create a gifcast for interactive-haskell-mode startup #824 <https://github.com/haskell/haskell-mode/issues/824> - Getting Stack overflow in regexp matcher error in Haskell module having more than 1500loc #830 <https://github.com/haskell/haskell-mode/issues/830> - C-u C-c C-t doesn't add type signature #900 <https://github.com/haskell/haskell-mode/issues/900> - Invoke hasktags more directly #964 <https://github.com/haskell/haskell-mode/issues/964> - Find a professional template for web presence #1117 <https://github.com/haskell/haskell-mode/issues/1117> - Indenting data types seems broken and not configurable #1125 <https://github.com/haskell/haskell-mode/issues/1125> - Syntax propertize could mark layout blocks #1164 <https://github.com/haskell/haskell-mode/issues/1164> - Support non-interactive completions #1171 <https://github.com/haskell/haskell-mode/issues/1171> - Remove haskell-doc-prelude-types from haskell-doc.el #1179 <https://github.com/haskell/haskell-mode/issues/1179> - Deprecate haskell-mode-contextual-space #1182 <https://github.com/haskell/haskell-mode/issues/1182> - Paredit M-s no longer works after upgrade to 13.18 #1183 <https://github.com/haskell/haskell-mode/issues/1183> - Extend non-interactive completions for identifiers from TAGS #1184 <https://github.com/haskell/haskell-mode/issues/1184> - Syntax highlighting is broken for list comprehensions #1185 <https://github.com/haskell/haskell-mode/issues/1185> - haskell-mode and delete-trailing-whitespace delete content of buffer on save #1188 <https://github.com/haskell/haskell-mode/issues/1188> - Indentation is broken for quasiquotation with quote symbols #1189 <https://github.com/haskell/haskell-mode/issues/1189> - Error: (void-function haskell--rx-let) #1209 <https://github.com/haskell/haskell-mode/issues/1209> - Check if haskell-mode-autoloads.el really loads #1210 <https://github.com/haskell/haskell-mode/issues/1210> - haskell-ident-pos-at-point does not work for operators #1213 <https://github.com/haskell/haskell-mode/issues/1213> - REPL often hangs inside :{ and :} #1221 <https://github.com/haskell/haskell-mode/issues/1221> - haskell-mode-contextual-space binding on the wiki is preventing space insertion #1222 <https://github.com/haskell/haskell-mode/issues/1222> - Font-lock misidentifying valid non-TH haskell as quasiquote #1223 <https://github.com/haskell/haskell-mode/issues/1223> - Regression in indentation logic #1232 <https://github.com/haskell/haskell-mode/issues/1232> - Fix inferior-haskell-send-decl-post-filter #1240 <https://github.com/haskell/haskell-mode/issues/1240> - Error message when hitting space bar #1242 <https://github.com/haskell/haskell-mode/issues/1242> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-March-20…>Pull requests merged in February - Add haskell-interactive-copy-to-prompt. #457 <https://github.com/haskell/haskell-mode/pull/457> - Remove suggested imports completely #1121 <https://github.com/haskell/haskell-mode/pull/1121> - Stylish haskell after save #1137 <https://github.com/haskell/haskell-mode/pull/1137> - Add a test for indentation broken on a quasiquote #1190 <https://github.com/haskell/haskell-mode/pull/1190> - Remove haskell-mode-contextual-space #1191 <https://github.com/haskell/haskell-mode/pull/1191> - Add chapter about spell checking #1192 <https://github.com/haskell/haskell-mode/pull/1192> - Make haskell-indent-region do nothing #1193 <https://github.com/haskell/haskell-mode/pull/1193> - Prevent automatic haskell-doc-mode actions when point in string or comment #1195 <https://github.com/haskell/haskell-mode/pull/1195> - Treat insides of quasiquotes as strings #1196 <https://github.com/haskell/haskell-mode/pull/1196> - Add comma list test for indentation #1198 <https://github.com/haskell/haskell-mode/pull/1198> - Add c2hs mode #1199 <https://github.com/haskell/haskell-mode/pull/1199> - Change a couple hook properties #1201 <https://github.com/haskell/haskell-mode/pull/1201> - Fix some warnings #1202 <https://github.com/haskell/haskell-mode/pull/1202> - Small improvements of completion functions #1203 <https://github.com/haskell/haskell-mode/pull/1203> - Invoke hasktags more directly #1204 <https://github.com/haskell/haskell-mode/pull/1204> - Few doc improvements and a bit of refactoring #1205 <https://github.com/haskell/haskell-mode/pull/1205> - Keep window position when spellchecking #1207 <https://github.com/haskell/haskell-mode/pull/1207> - Improve fonts in manual #1208 <https://github.com/haskell/haskell-mode/pull/1208> - Makefile dependency tracking improvements #1211 <https://github.com/haskell/haskell-mode/pull/1211> - C2hs fixes #1212 <https://github.com/haskell/haskell-mode/pull/1212> - Guard against tabs in elisp files #1214 <https://github.com/haskell/haskell-mode/pull/1214> - Return removed names for backward compatibility #1215 <https://github.com/haskell/haskell-mode/pull/1215> - Handle operators in haskell-ident-pos-at-point too #1224 <https://github.com/haskell/haskell-mode/pull/1224> - Move haskell-interactive-prompt-state related definitions to haskell-utils.el #1226 <https://github.com/haskell/haskell-mode/pull/1226> - Extend static completions with candidates from tags table #1228 <https://github.com/haskell/haskell-mode/pull/1228> - Update completion section #1230 <https://github.com/haskell/haskell-mode/pull/1230> - Small docs improvements #1233 <https://github.com/haskell/haskell-mode/pull/1233> - Remove unused indent-region from menu #1236 <https://github.com/haskell/haskell-mode/pull/1236> - Be more strict about quasi quoter names #1239 <https://github.com/haskell/haskell-mode/pull/1239> - Use plain syntax in inferior-haskell-send-decl-post-filter #1241 <https://github.com/haskell/haskell-mode/pull/1241> <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-March-20…>Contributors active in February Arthur Fayzrakhmanov (Артур Файзрахманов), Artyom, Fice T, Gracjan Polak, Sergey Vinokurov <https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-March-20…> Contributing Haskell Mode needs volunteers like any other open source project. For more information see: https://github.com/haskell/haskell-mode/wiki Also drop by our IRC channel: #haskell-emacs at irc.freenode.net. Thanks!

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Haskell hacking internships at LANL (Fall 2016, undergraduate)
by Kei Davis 01 Apr '16

01 Apr '16

We have an ongoing project developing an auto-parallelizing pure functional language implementation using GHC as the front end to dump Core or STG (much like Intel's approach here http://www.leafpetersen.com/leaf/publications/hs2013/hrc-paper.pdf) If you are a United States citizen or permanent resident alien studying computer science or mathematics at the undergraduate level with strong interests in Haskell programming, compiler/runtime development, and pursuing a fall semester (2016) internship at Los Alamos National Laboratory this could be for you. We don't expect applicants to necessarily already be highly accomplished Haskell programmers--such an internship is expected to be a combination of (further) developing your programming/Haskell skills and putting them to good use. If you're already a strong C hacker we could use that too. The application deadline is May 31, 2016. It's a bit of a process so don't leave inquiries until the last day. Email me if interested in more information, and feel free to pass this along. -- Kei Davis kei(a)lanl.gov Applied Computer Science Group CCS-7, Mail Stop B287 Los Alamos National Laboratory Los Alamos, NM 87545, U.S.A.

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[TFP 2016] Final call for papers
by Peter Achten 01 Apr '16

01 Apr '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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Deriving Eq and Show instances for testing
by Anakreontas 01 Apr '16

01 Apr '16

I have datatypes for which I need an Eq and Show instance only for testing. I could derive those instances in the datatype declaration but I prefer not to add unnecessary functionality. With StandaloneDeriving extension I can derive the instances in the test module but this produces many warning about orphan instances. Is there a better approach or a way to stop reports about orphan instance warnings? Regards

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Re: [Haskell-cafe] [Haskell] Postdoc ad: quantum-computing programming languages
by Jerzy Karczmarczuk 01 Apr '16

01 Apr '16

Hello. Le 31/03/2016 22:04, Scott Pakin a écrit : > My institution just bought a D-Wave 2X adiabatic quantum computer. > The problem is, no one really has a grasp on how to *program* an > adiabatic quantum computer. It's a totally different beast from the > gate-model quantum computers that most people imply when they talk > about quantum computing. I find all this a bit disturbing... Los Alamos buys an expensive device that nobody knows how to use?? Moreover, in circumstances where the doubts about the real performance of the D-Wave computer stii persist? Several physicists refuse to call this contraption a "quantum computer". The statements about their "qubits" in their public materials are not always serious, there is practically nothing about a genuine state superposition, no educated physicist will buy such pseudo-definition as "having simultaneously the values 0 and 1" (being the result of two currents flowing in opposite directions ; what about phase?). Their "white paper" about the map colouring shows a model which is more similar to a Hopfield (or similar) neural network, rather than a quantum computing device. The optimization is a natural application domain of such networks, but where are some more universal examples? Surely, there are quantum elements in it: superconducting niobium rings, Josephson junctions, etc. But, actually, even a plain transistor is a quantum device as well, and nobody dares to call it a "qubit". Their native code seems to be extremely far from quantum theory, as we know it. = But, if the device works, has some affinities with neural stuff and with Monte-Carlo techniques (annealing), perhaps a good playground for testing it would be a Go player? Jerzy Karczmarczuk

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introspection -- towards type algebra
by Rustom Mody 01 Apr '16

01 Apr '16

I am looking for how far algebra on types in the manner of "set theory as an algebra" ¹ is possible. So for example in set theory one can compute for sets S, T S∪T, S∩T, S-T etc Is something similar possible for types? Say I have data Primary = Red|Green|Blue data Othercolors = Violet|Indigo|Yellow|Orange I want something like Rainbow = Primary ∪ Othercolors Equivalently if Rainbow and Primary had been defined, how to get/compute Rainbow - Primary? ------------------------- I thought the first-class types in Idris would be a good bet to try out at least a trivial prototype. Seems not... So asking here. Clearly and obviously one can use haskell to implement any language. My question is what/which are the introspective libraries/features of modern haskell that make this easy and lightweight. Thanks Rusi ¹ Yeah the term 'type algebra' may be taken in the sense of algebraic data types Cant think of a better one

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Postdoc ad: quantum-computing programming languages
by Scott Pakin 31 Mar '16

31 Mar '16

My institution just bought a D-Wave 2X adiabatic quantum computer. The problem is, no one really has a grasp on how to *program* an adiabatic quantum computer. It's a totally different beast from the gate-model quantum computers that most people imply when they talk about quantum computing. I'm looking to hire a postdoc to work with me on designing and implementing programming models suitable for execution on D-Wave-style quantum computers. The formal job ad can be found at http://tinyurl.com/jdlo556 or go to http://jobs.lanl.gov/ and look up job IRC49031. Disclaimer: This is not specifically a Haskell-hacking position, although you can use any language you want for the classical-side development. I'm posting here because a key skill I'm looking for is breadth of language knowledge. I see a candidate who knows nonstrict functional programming, declarative programming, and maybe a few "fringe" programming models as more valuable than one who knows only a dozen isomorphic imperative languages. -- Scott

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hslua and language-lua need new maintainers
by Ömer Sinan Ağacan 31 Mar '16

31 Mar '16

Hi all, I need new maintainers for my packages hslua[1] and language-lua[2]. None of these packages is super popular so it's not going to be a lot of work. I just need someone to take care of new issues and pull requests. + points if the maintainer is a user of the library :-) I just don't have time and motivation to maintain those as I'm not a user anymore. Some background, lanugage-lua was the first Haskell program I've written (according to git logs, 3 years 6 months ago). I maintained it over the years and used in some projects. Currently Eric Mertens (glguy) is also a maintainer who occasionally sends some patches, but I need someone to take care of the new issues and pull requests. One thing you may want to do is to merge Eric's patch that ports the parser to Happy (currently it's Parsec) and improves the performance significantly. hslua was originally written by Gracjan Polak. I was using it and sending some patches and eventually I became the maintainer, created a Git repo, wrote some blogs posts about it, wrote tests and examples etc. I think the library is in good shape. One thing you may want to do if you take over the maintainership might be to port it to Lua 5.3 and drop the LuaJIT support. Every once in a while someone asks for it, there's even a pull request that is in bad shape that makes it working with 5.3. There's also another feature request for handling memory exhaustion in the interpreter. If you're interested in maintaining any of these please reply to this thread or send me a mail. Thanks. --- [1]: http://hackage.haskell.org/package/hslua [2]: http://hackage.haskell.org/package/language-lua

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ghc 7.10.3 crashes frequently on Windows
by Anakreontas 31 Mar '16

31 Mar '16

I have installed ghc from Haskell Platform version 7.10.3. When I run QuickCheck or HSpec tests interactively, every so often ghc crashes when I reload a file form withing Emacs and haskell mode. This problem manifested in earlier versions as well. Loading a file which does not contain tests never crashes ghc so far. How could I try to identify the cause of the crash?

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cabal: --enable-tests by default
by Andrew Pennebaker 31 Mar '16

31 Mar '16

In the future, could cabal --enable-tests by default when `cabal install`ing local project directories? Other languages' package managers automatically do this, a more intuitive default behavior. -- Cheers, Andrew

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Melbourne Haskell Users Group Meetup, Tonight, 31-03-2016 @ 6:30pm
by Lyndon Maydwell 30 Mar '16

30 Mar '16

Hi All, Tonight we're having our monthly Haskell meetup in the Melbourne CBD. Please come along if you're interested and free! http://www.meetup.com/Melbourne-Haskell-Users-Group/events/228915323/ Hope to see you there :) Regards, - Lyndon

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parsec reorganization
by Rustom Mody 30 Mar '16

30 Mar '16

Ive been trying parsec And I gather that the modules structures are heavily reorganized eg https://kunigami.wordpress.com/2014/01/21/an-introduction-to-the-parsec-lib… starts with import Data.Char (char) which immediately gives Module ‘Data.Char’ does not export ‘char’ Change that to import Text.Parsec.Char (char) and that error goes and more and more arcane ones start Likewise all the stuff here http://jakewheat.github.io/intro_to_parsing/ seems to be wrong paths Is there no tutorial for the current versions? ghc 7.8.4 parsec 3.1.9-2

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[2nd CFP] Haskell Symposium 2016
by Geoffrey Mainland 30 Mar '16

30 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. Papers may be submitted at: https://icfp-haskell2016.hotcrp.com/ 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 =====================================================================

2 1

Hspec + QuickCheck passing type
by Martijn Rijkeboer 29 Mar '16

29 Mar '16

Hi, I'm writing the following Hspec + QuickCheck test for some type: context "Type1" $ it "decode inverses encode" $ property $ \x -> (decode . encode) x == Right (x::Type1) However, I have a number of these types, and I could write the same test for every type, but that isn't very DRY. Therefore I would like to put the test in a function and call that function for every type. Something like the following: typeTest name = do context name $ it "decode inverses encode" $ property $ \x -> (decode . encode) x == Right x Unfortunately this doesn't work, since QuickCheck doesn't know which Arbitrary instance to use. How can I pass the type, e.g. x::Type1, to this function so QuickCheck knows what Arbitrary instance to use? Kind regards, Martijn Rijkeboer

3 3

Type equality with "forall"
by Oleg 29 Mar '16

29 Mar '16

There are no problems in the code you have posted so far: it works exactly as it is supposed to. Overlapping instances worked as designed. It seems the problem is not in Haskell but in your expectations of existentials. Existentials are a means of abstraction, that is, deliberately forgetting details. In our case, forgetting all the details about the type. Consider the following code data W where Wrap :: a -> W test1 = case Wrap True of Wrap x -> not x It does not type-check. The variable x in test1 has the type which is different from any other existing type. Therefore, you cannot do anything sensible with it -- in particular, you cannot apply 'not', which works only for Booleans. Can't GHC just see that ``x is Bool'' -- just look at the line above!? No, by using the existential you specifically told GHC to forget all it knows about the type of the Wrapped value. If you want to remember some information about the existential type, you have to do it explicitly. For example, you can use Typeable and cast data W where Wrap :: Typeable a => a -> W test1 = case Wrap True of Wrap x' | Just x <- cast x' -> not x Wrap _ -> error "not a Bool" or build your own Universe (if you know in advance all the types you will be working with) data TypeRep a where TInt :: TypeRep Int TBool :: TypeRep Bool TArr :: TypeRep a -> TypeRep b -> TypeRep (a -> b) data W where Wrap :: TypeRep a -> a -> W test1 :: Bool test1 = case Wrap TBool True of Wrap TBool x -> not x Wrap _ _ -> error "not a Bool" In the latter case, the type signature is required. Basically, you have to write signature for every function that pattern-matches on the real GADTs (sometimes you can get away; but oftentimes you'll get a really cryptic error message instead). The latter pattern, using TypeRep, is the foundation of basically all generic programming out there.

1 0

Munich Haskell Meeting, 2015-03-30 @ 19:30
by Christian Neukirchen 28 Mar '16

28 Mar '16

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Wednesday, March 30 at Cafe Puck at 19h30. For details see here: http://chneukirchen.github.io/haskell-munich.de/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-mar-2016/ Everybody is welcome! -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

1 0

build error using hsqml
by Fabien R 27 Mar '16

27 Mar '16

Hello, I'm trying to build a program using HsQml. cabal 1.14.0 fails with this error: Building HsQmlTest-0.0.1... Preprocessing executable 'HsQmlTest' for HsQmlTest-0.0.1... [1 of 1] Compiling Main ( src/Main.hs, dist/build/HsQmlTest/HsQmlTest-tmp/Main.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.4.0.0 ... linking ... done. Loading package deepseq-1.3.0.0 ... linking ... done. Loading package containers-0.4.2.1 ... linking ... done. Loading package filepath-1.3.0.0 ... linking ... done. Loading package tagged-0.4.2.1 ... linking ... done. Loading package bytestring-0.9.2.1 ... linking ... done. Loading package text-0.11.2.0 ... linking ... done. Loading package transformers-0.3.0.0 ... linking ... done. <command line>: can't load .so/.DLL for: /home/fabien/.cabal/lib/hsqml-0.3.4.0/ghc-7.4.1/libcbits-hsqml-0.3.4.0.so (libQt5Widgets.so.5: cannot open shared object file: No such file or directory) Loading package hsqml-0.3.4.0 ... Using --extra-lib-dirs to set the path of the library does not improve the situation. Here is the cabal description: name: HsQmlTest version: 0.0.1 cabal-version: >=1.2 build-type: Simple license: AllRightsReserved license-file: "" description: data-dir: "" executable HsQmlTest build-depends: QuickCheck -any, base -any, hsqml -any, text -any main-is: Main.hs buildable: True cpp-options: -DMAIN_FUNCTION=exeMain extra-lib-dirs: /media/travail/debian-sources/qt5/qtbase/lib/ hs-source-dirs: src Any hint ? -- Fabien

3 4

HGamer3D has a new dependency installer
by Peter Althainz 26 Mar '16

26 Mar '16

Dear All, it took a long while, but now a new solution has been found for dependency setup for HGamer3D. What do you think? Check here: http://www.hgamer3d.org/Install.html . regards uotbw

1 0

[ANN] Csound-expression-5 is out (framework for computer music)
by Anton Kholomiov 26 Mar '16

26 Mar '16

I'd like to announce a new version of Csound-expression library. It's a framework for computer music production. It compiles Haskell code to Csound. What's new? **The 5.0 is out! New features:** csound-expression * **Microtonal tunings**. We can use custom temperaments with insturments, patches, soundfonts and MIDI-instruments. Check out the guide on tuning and microtonal music (see also module `Csound.Tuning`). There are many predefined tunings (including ancient ones). Now we can play the authentic Bach music with Haskell! See [Custom temperament. Microtonal music]( https://github.com/anton-k/csound-expression/blob/master/tutorial/chapters/… ) for details. * **Functions for Csound API**. We can interface with generated code through many other languages. We can generate the code with Haskell and the use it in other environments. we can build UI with Python or Clojure, we can create an Android synthesizer. See the guide section on Csound API. See [Csound API. Using generated code with another languages]( https://github.com/anton-k/csound-expression/blob/master/tutorial/chapters/… ) for details. * **Padsynth algorithm** (need Csound 6.05). There are functions that makes it easy to use wonderful PADsynth algorithm, This algorithm is designed to make "alive" instruments, natural pads. There are not only function that explore the algorithm but also new PAtches in the package csound-catalog that are based on it! See the section in the guide on the PADsynth. Lot's of padsynth instruments are mode with morphing support. We can crossfade between 2 or even 4 timbres. See [Padsynth algorithm]( https://github.com/anton-k/csound-expression/blob/master/tutorial/chapters/… ) for details. * **Argument modifiers** make it very convinient to modulate the rguments (apply vibrato to frequency or add some randomness to the parameter). See [Arguments modulation]( https://github.com/anton-k/csound-expression/blob/master/tutorial/chapters/… ) for details. * The **hard clipping** was substituted with **limiter**. There should be no distortion when amplitude goes higher than `0dbfs` value. * Adds **Ping-pong delay** implementation. See function `pingPong` at the module `Csound.Air.Fx`. * Adds Rory Walsh's brand **new analog filters** (need Csound 6.07). See functions `alp1`, `alp2` and `alp3` at the module `Csound.Air.Filter`. * Bugfixes for `mixAt` function. Now it doesn't duplicates the effectful-code. Now `mixAt` is not a function that is based on class `At`. It becomes a method in it's own class called `MixAt`. That fixes the code duplication problem. csound-catalog * **new instruments** that are based on **PADsynth algorithm**. Check out `Csound.Patch` at the section on PADsynth Sharc instruments. There are new deep spiritual vedic pads (vibhu, rishi, agni, prakriti, rajas, avatara, bhumi). See [Padsynth algorithm]( https://github.com/anton-k/csound-expression/blob/master/tutorial/chapters/… ) for details. Link to the library: http://hackage.haskell.org/package/csound-expression Github repo: https://github.com/spell-music/csound-expression You can listen to some PADsynth instruments at the link: https://www.dropbox.com/s/pqn4dkvoo01dome/ce-5.zip?dl=0 Cheers, Anton

1 0

Lightweight Unicode normalization library
by Harendra Kumar 25 Mar '16

25 Mar '16

I looked around and found only one package, text-icu which provides unicode normalization operations and a lot more. But text-icu depends on the icu library being installed on the system. We would prefer to avoid dependency on the icu library. Is there a lightweight alternative which does not depend on icu? It could be a pure Haskell package or bindings to a lightweight C library where the library is small and shipped with the package itself. I wonder if there is a need for unicode normalization operations in GHC code itself? If so how does it handle that? I found a lightweight C library (https://github.com/JuliaLang/utf8proc) for normalization and case folding used by the Julia lang project. If there is no other option I am considering creating bindings to this library. Any pointers, thoughts? Thanks, Harendra

2 3

Docs pending for a long time, on Hackage
by Henk-Jan van Tuyl 25 Mar '16

25 Mar '16

L.S., There is no documentation for the most recent version of package wx[0], even though it is on Hackage since December last year. It's Hackage page says: Status Docs pending Build status unknown [no reports yet] Why is this and how can I get the build started? Regards, Henk-Jan van Tuyl [0] https://hackage.haskell.org/package/wx-0.92.2.0 -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

1 0

[ANN] task-distribution: simple distribution of new code in a cluster computing setup
by Axel Mannhardt 24 Mar '16

24 Mar '16

Hello cafe, I am happy to announce task-distribution, a framework written in order to distribute and execute tasks as fast as possible on a large data set. Its accentuation is that it supports distributing new logic to other nodes from within the program itself, thus avoiding both restarting slave node processes and a separated plugin-management infrastructure. An example use case is running continuously changing analytics logic on a given data set stored in HDFS. Avalailable on hackage and github: https://github.com/michaxm/task-distribution Cheers, Axel

1 0

Three Haskell dev roles at Standard Chartered
by Don Stewart 23 Mar '16

23 Mar '16

Hi all I'm hiring another 3 devs to join Strats at Standard Chartered in London or Singapore. This is a good chance to join a growing, experienced team using Haskell for a wide set of projects in finance. More details in https://donsbot.wordpress.com/2016/03/23/haskell-developer-roles-at-standar… -- Don

1 0

Haskell-related PhD Studentship at Kent
by Meng Wang 22 Mar '16

22 Mar '16

Dear Haskellers, I am seeking a PhD student on a Haskell-related project: http://www.cs.kent.ac.uk/research/studyingforaphd/phd-wang.html This would be a good opportunity for someone who is interested in applying Haskell ideas to real problems. The funding covers maintenance, EU student fees and research related expenses. But non-EU students are welcome to apply too. For Sep 2015 starting, the application deadline is 17 April 2015. If you are interested, please contact me at m.w.wang(a)kent.ac.uk<mailto:m.w.wang@kent.ac.uk>. Best wishes, Meng — Dr Meng Wang School of Computing University of Kent http://www.cs.kent.ac.uk/people/staff/mw516/

1 1

[TFPIE 2016] 2nd call for papers
by Peter Achten 22 Mar '16

22 Mar '16

Trends in Functional Programming in Education (TFPIE 2016) 2nd Call for papers https://wiki.science.ru.nl/tfpie/TFPIE2016 The 5th International Workshop on Trends in Functional Programming in Education, TFPIE 2016, will be held on June 7, 2016 at the University of Maryland College Park in the USA. It is co-located with the Symposium on Trends in Functional Programming (TFP 2016) which takes place from June 8 - 10. *** Goal *** The goal of TFPIE is to gather researchers, teachers and professionals that use, or are interested in the use of, functional programming in education. TFPIE aims to be a venue where novel ideas, classroom-tested ideas and work-in-progress on the use of functional programming in education are discussed. The one-day workshop will foster a spirit of open discussion by having a review process for publication after the workshop. The program chair of TFPIE 2016 will screen submissions to ensure that all presentations are within scope and are of interest to participants. Potential presenters are invited to submit an extended abstract (4-6 pages) or a draft paper (up to 16 pages) in EPTCS style. The authors of accepted presentations will have their preprints and their slides made available on the workshop's website/wiki. Visitors to the TFPIE 2016 website/wiki will be able to add comments. This includes presenters who may respond to comments and questions as well as provide pointers to improvements and follow-up work. After the workshop, presenters will be invited to submit (a revised version of) their article for review. The PC will select the best articles for publication in the journal Electronic Proceedings in Theoretical Computer Science (EPTCS). Articles rejected for presentation and extended abstracts will not be formally reviewed by the PC. TFPIE workshops have previously been held in St Andrews, Scotland (2012), Provo Utah, USA (2013), Soesterberg, The Netherlands (2014), and Sophia-Antipolis, France (2015). *** Program Committee *** Stephen Chang at Northeastern University in Massachusetts, USA Marc Feeley at Université de Montréal in Québec, Canada Patricia Johann at Appalachian State University in North Carolina, USA Jay McCarthy at University of Massachusetts Lowell in Massachusetts, USA (Chair) Prabhakar Ragde at University of Waterloo in Ontario, Canada Brent Yorgey at Hendrix College in Arkansas, USA *** Submission Guidelines *** TFPIE 2016 welcomes submissions describing techniques used in the classroom, tools used in and/or developed for the classroom and any creative use of functional programming (FP) to aid education in or outside Computer Science. Topics of interest include, but are not limited to: - FP and beginning CS students - FP and Computational Thinking - FP and Artificial Intelligence - FP in Robotics - FP and Music - Advanced FP for undergraduates - Tools supporting learning FP - FP in graduate education - Engaging students in research using FP - FP in Programming Languages - FP in the high school curriculum - FP as a stepping stone to other CS topics - FP and Philosophy *** Best Lectures *** In addition to papers, we request "best lecture" presentations. What is your best lecture topic in an FP related course? Do you have a fun way to present FP concepts to novices or perhaps an especially interesting presentation of a difficult topic? In either case, please consider sharing it. Best lecture topics will be selected for presentation based on a short abstract describing the lecture and its interest to TFPIE attendees. *** Submission *** Papers and abstracts can be submitted via EasyChair at the following link: https://easychair.org/conferences/?conf=tfpie2016 It is expected at at least one author for each submitted paper will attend the workshop. *** Registration & Local Information *** Please see the TFP site for registration and local information: http://tfp2016.org/ *** Important Dates *** April 27, 2016: Submission deadline for draft TFPIE papers and abstracts May 3, 2016: Notification of acceptance for presentation May 13, 2016: Registration for TFP/TFPIE closes June 7, 2016: Presentations in Maryland, USA July 7, 2016: Full papers for EPTCS proceedings due. September 1, 2016: Notification of acceptance for proceedings September 22, 2016: Camera ready copy due for EPTCS Submission of an abstract implies no obligation to submit a full version; abstracts with no corresponding full versions by the full paper deadline will be considered as withdrawn.

1 0

Stuck on a type family problem where kind inference fails
by Oliver Charles 21 Mar '16

21 Mar '16

Hi all, This is a little tricky to explain, so bear with me. I'm working on some code that roughly models a PostgreSQL schema. Users begin by defining their tables as Haskell records, parametrized over some f :: k -> *, and use a special Col type family that applies some normalisation: data Table f = Table { tableId :: Col f ('NotNullable 'DBInt) , tableX :: Col f ('Nullable 'DBString) } is one such example. The idea behind Col is that sometimes we don't need information about the "full type" when we know more about f. One such choice of f is Expr, which corresponds to expressions inside a query. In this case, I would desire tableId :: Col Expr ('NotNullable 'DBInt) = tableId :: Expr 'DBInt tableX :: Col Expr ('Nullable 'DBString) = tableX :: Expr ('Nullable 'DBString) Notice here that if you use 'NotNullable, then this information is erased - but it's important if the column is 'Nullable. However, I'm struggling to work out any way to actually pull this off in the general case. Here's what I've been attempting: {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE RankNTypes #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE KindSignatures #-} {-# LANGUAGE PolyKinds #-} {-# LANGUAGE TemplateHaskell #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE ScopedTypeVariables #-} module ExprTest where import Data.Singletons import Data.Singletons.Prelude hiding (Null) import Data.Singletons.TH data Expr (a :: k) data MyExprSym :: TyFun k * -> * type instance Apply MyExprSym (x :: k) = Expr x $(singletons [d| data Null a = Nullable a | NotNullable a |]) $(promote [d| notNullableType k (NotNullable a) = baseType k a nullableType k (Nullable a) = baseType (k . Nullable) a baseType k a = k a |]) So far, this seems to work well. If I ask GHCI: *ExprTest> :kind! Apply (Apply NullableTypeSym0 MyExprSym) ('Nullable 'DBString) Apply (Apply NullableTypeSym0 MyExprSym) ('Nullable 'DBString) :: * = Expr ('Nullable 'DBString) *ExprTest> :kind! Apply (Apply NotNullableTypeSym0 MyExprSym) ('NotNullable 'DBInt) Apply (Apply NotNullableTypeSym0 MyExprSym) ('NotNullable 'DBInt) :: * = Expr 'DBInt This is exactly what I want, but note that I had to choose the necessary symbols NullableTypeSym0 and NotNullableTypeSym0. I would like to calculate those symbols from the column type itself. Looking at the kinds of these symbols though, they are both different: *ExprTest> :kind! NotNullableTypeSym0 NotNullableTypeSym0 :: TyFun (TyFun k1 k -> *) (TyFun (Null k1) k -> *) -> * = NotNullableTypeSym0 *ExprTest> :kind! NullableTypeSym0 NullableTypeSym0 :: TyFun (TyFun (Null k1) k -> *) (TyFun (Null k1) k -> *) -> * = NullableTypeSym0 So I can't see a way to write a single type family that returns them. To summarise, I'd like a way to write this following instance for Col: type instance Col Expr x = Apply (Apply ?? MyExprSym) x such that Col Expr ('Nullable a) = Expr ('Nullable a') and Col Expr ('NotNullable a) = Expr a but I cannot work out how to write the placeholder ?? above. One attempt is type family ExprTyfun (col :: colK) :: TyFun (TyFun k * -> *) (TyFun j * -> *) -> * type instance ExprTyfun ('NotNullable a) = NotNullableTypeSym0 type instance ExprTyfun ('Nullable a) = NullableTypeSym0 But neither of these instances actually normalise as I'd like, presumably because of k and j being forall'd in the return type: *ExprTest> :set -fprint-explicit-kinds *ExprTest> :kind! ExprTyfun ('Nullable 'DBInt) ExprTyfun ('Nullable 'DBInt) :: TyFun (TyFun k * -> *) (TyFun k1 * -> *) -> * = ExprTyfun k k1 (Null DBType) ('Nullable DBType 'DBInt) *ExprTest> :kind! ExprTyfun ('NotNullable 'DBInt) ExprTyfun ('NotNullable 'DBInt) :: TyFun (TyFun k * -> *) (TyFun k1 * -> *) -> * = ExprTyfun k k1 (Null DBType) ('NotNullable DBType 'DBInt) *ExprTest> :i ExprTyfun type family ExprTyfun (k :: BOX) (j :: BOX) (colK :: BOX) (col :: colK) :: TyFun (TyFun k * -> *) (TyFun j * -> *) -> * -- Defined at src/Opaleye/TF/ExprTest.hs:39:1 type instance ExprTyfun (Null k) (Null k) (Null k1) ('Nullable k1 a) = NullableTypeSym0 * k -- Defined at src/Opaleye/TF/ExprTest.hs:41:1 type instance ExprTyfun k (Null k) (Null k1) ('NotNullable k1 a) = NotNullableTypeSym0 * k -- Defined at src/Opaleye/TF/ExprTest.hs:40:1 I'd also like to point out that in my full code the types to Col can be a lot bigger, and I'd like to not assume any ordering. For example, here's a possible type: userId :: Col f ('Column "id" ('NotNullable ('HasDefault 'DBInt))) In this case Col Expr ('Column "id" ('NotNullable ('HasDefault 'DBInt))) = Expr 'DBInt I hope this question is understandable! Please let me know if there's anything I can do to provide more clarity. - Ollie

2 10

Using rebox2 (emacs) with Haskell
by Henry Laxen 21 Mar '16

21 Mar '16

If any of you have tried using rebox2 with haskell, you've discovered that it does not have a built in Haskell comment mode. I was looking for something like this: ------------------------------------- -- You can put a nice comment here -- -- and surround with a pretty box -- ------------------------------------- Actually, it is easy to set this up with a few lines in your .emacs file. Here is what you need: (require 'rebox2) (add-to-list 'rebox-language-character-alist '(7 . "-")) (setq rebox-style-loop '(725)) (rebox-register-all-templates) (add-hook 'haskell-mode-hook 'rebox-mode) Then just type Meta-q if you want to refill the comment, and Meta-Q if you don't want to refill. I hope this is helpful. Best wishes, Henry Laxen

1 0

Odd list comprehension behaviour
by Krisztian Pinter 21 Mar '16

21 Mar '16

Hello, I noticed some odd behaviour with list comprehensions. [1..1] == [1] BUT [1,1..1] == [1..] I noticed this while writing a Clean program, but it seems Haskell inherited this as well. In the case of integer lists with step size >= 0 the up_list function[1] is used: up_list :: Integer -> Integer -> Integer -> [Integer] up_list x0 delta lim = go (x0 :: Integer) where go x | x > lim = [] | otherwise = x : go (x+delta) In the case of [1,1..1] x0 == lim, so go will recurse infinitely, producing an infinite list. I think the reasonable behaviour would be [1,1..1] == [1]. Is there a reason it doesn't work like this? [1] http://hackage.haskell.org/package/base-4.8.2.0/docs/src/GHC.Enum.html#up_l… Thanks, Krisztián

9 14

Ambiguous type variable ‘f0’ arising from a use of ‘f’
by Tom Ellis 20 Mar '16

20 Mar '16

Can anyone explain what happened in GHC 8 such that it forced this change: -data PackMap a b s t = PackMap (Applicative f => (a -> f b) -> s -> f t) +data PackMap a b s t = PackMap (forall f. Applicative f => (a -> f b) -> s -> f t) ... instance PP.SumProfunctor (PackMap a b) where - f +++! g = (PackMap (\x -> eitherFunction (f' x) (g' x))) - where PackMap f' = f - PackMap g' = g + f +++! g = + PackMap (\x -> + case f of + PackMap f' -> + case g of + PackMap g' -> + eitherFunction (f' x) + (g' x)) https://github.com/tomjaguarpaw/haskell-opaleye/pull/140/files The errors are Ambiguous type variable ‘f0’ arising from a use of ‘f’ etc., as seen here https://github.com/tomjaguarpaw/haskell-opaleye/pull/140#issuecomment-19829… Thanks, Tom

2 5

Gaussian Elimination over GF2
by Mick Francis 20 Mar '16

20 Mar '16

Does anyone know of any implementation in Haskell of Gaussian Elimination over GF2? I'm experimenting with congruence-based factoring algorithms, and need an implementation for the Linear Algebra stage. Mick.

1 0

[ANN] servant 0.5
by Julian Arni 19 Mar '16

19 Mar '16

Dear all, We have just released a new major version (0.5) of the official servant packages: - servant - servant-server - servant-client - servant-docs - servant-foreign - servant-js - servant-cassava - servant-blaze - servant-lucid - servant-mock (servant-js and servant-foreign are being released for the first time. servant-jquery will be deprecated in favour of servant-js) This new version brings quite a number of significant changes. Servant is now faster, more correct, more replete with features, and more consistent. We have a blog post going into more details about the changes: http://haskell-servant.github.io/posts/2016-03-19-servant-0.5-release.html Note also that we have revamped our tutorial, and moved it to readthedocs: http://haskell-servant.readthedocs.org/en/master/ Enjoy the weekend, Julian

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 151, Issue 22
by Barak A. Pearlmutter 19 Mar '16

19 Mar '16

> If I were to propose this, which I'm not, I would discuss what the > [a,b..c] notation is meant to represent. To me, personally and for no > good reason, it looks like an iterator that yields numbers starting at > a, adding (b-a) at each step and yielding the next number as long as > it's less than or equal to c, and continuing as long as c is neither > reached nor exceeded. Yes, the current situation is somewhat odd. $ ghci GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help Prelude> [0,5..9] [0,5] Prelude> [0,0.5..0.9] [0.0,0.5,1.0] Prelude> [0.0..0.49999999999999991] [0.0] Prelude> [0.0..0.49999999999999992] [0.0,1.0] Prelude> :m Data.Ratio Prelude Data.Ratio> [0..1%2] [0 % 1,1 % 1] This makes the construct into a serious bug generator for anything numeric. For instance, consider a naive numeric integration of the sort one might wish to exhibit while teaching Haskell this past pi day, Monday the fourteenth of March. Prelude> let h=1e-1 in sum $ map (\x -> 4*h*sqrt(1-x^2)) [0,h..1] 3.304518326248318 Prelude> let h=1e-2 in sum $ map (\x -> 4*h*sqrt(1-x^2)) [0,h..1] NaN Prelude> let h=1e-3 in sum $ map (\x -> 4*h*sqrt(1-x^2)) [0,h..1] NaN Prelude> let h=1e-4 in sum $ map (\x -> 4*h*sqrt(1-x^2)) [0,h..1] 3.141791477784753 Prelude> let h=1e-5 in sum $ map (\x -> 4*h*sqrt(1-x^2)) [0,h..1] 3.1416126164824103 Prelude> let h=1e-6 in sum $ map (\x -> 4*h*sqrt(1-x^2)) [0,h..1] NaN One invariant that people seem to find natural regarding [x,y..z] is that its elements are all between x and z (inclusive), regardless of the value of y. This is, in part, because the mathematical notation [x,z] often denotes the closed interval whose endpoints are x and z. I myself cannot think of any advantage of the behaviour exhibited above. To take a slightly deeper violated invariant, it seems like map f [x,y..z] and [f x,f y..f z] should be the same when f is a linear (in the numeric sense) function. The current behaviour violates this.

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Re: [Haskell-cafe] Trying desperately to make a c library binding on Windows
by Nicu Ionita 18 Mar '16

18 Mar '16

Am 17.03.2016 um 23:24 schrieb Theodore Lief Gannon: > > I am on Win 7, using stack (configured for lts-4.2) under MinGW. > > Stack itself provides MSYS2/MinGW during builds on Windows. Do you > mean you have an independent MinGW shell that you're opening, and then > running stack from there? Yes, I work under the git bash (git for Windows comes with an own msys). > If so, assuming you're not already using this flag, try: > > stack build --skip-msys Just tried that now, same result. > > This tells stack that it's already running inside a unix-style shell, > and shouldn't assert its related path overrides. > > Beyond that, it would help to have more information about exactly > where everything is and how it's being built/invoked/etc. Project is under: J:\Projects\BaseOh Library is under: J:\BO\lib and is called: libbayesopt.a (under bash they are called /j/Projects/BaseOh and /j/BO/lib, needless to say I tried those too, but they are not found, as the programs know only Windows style paths). So beeing under the git bash in the project directory, I type: > stack build or even: > stack build --extra-lib-dirs=j:\\BO\\lib But in both cases, if the line "extra-libraries: bayesopt" is present in the cabal file, then configure does not work (message below). Inbetween I upgraded stack (now is version 1.0.4.2 x86_64). When I try to build, I get the message: Continuing despite missing tool: msys2 after which the build continues and brings exactly the same failures. > > On Thu, Mar 17, 2016 at 2:19 PM, Nicu Ionita <nicu.ionita(a)acons.at > <mailto:nicu.ionita@acons.at>> wrote: > > Hi all, > > I am really stuck with my try to make a Haskell binding for the > library bayesopt on Windows. > In theory it looks all simple, just put some lines in the cabal > configuration file: > > ... > extra-lib-dirs: /path/to/the/lib -- contains the file > libbayesopt.a > extra-libraries: bayesopt > ... > > But whatever I tried, I can't step over the configuration phase, > coz I get (I'm compiling with stack): > > Configuring BaseOh-0.1.0.0... > setup-Simple-Cabal-1.22.5.0-x86_64-windows-ghc-7.10.3.exe: Missing > dependency > on a foreign library: > * Missing C library: /j/BO/lib/libbayesopt.a > This problem can usually be solved by installing the system > package that > provides this library (you may need the "-dev" version). If the > library is > already installed but in a non-standard location then you can use > the flags > --extra-include-dirs= and --extra-lib-dirs= to specify where it is. > > If I comment those lines out, then the configure phase succeeds, > the library is compiled (i.e. my binding library), but a test > executable in the same project does of course not compile, as > symbols are missing: > > ... > In-place registering BaseOh-0.1.0.0... > Preprocessing executable 'test' for BaseOh-0.1.0.0... > [1 of 2] Compiling Optimisation.Stochastic.BayesOpt ( > src\Optimisation\Stochasti > c\BayesOpt.hs, > .stack-work\dist\x86_64-windows\Cabal-1.22.5.0\build\test\test-tm > p\Optimisation\Stochastic\BayesOpt.o ) > ghc.exe: unable to load package `BaseOh-0.1.0.0' > ghc.exe: > J:\Projects\BaseOh\.stack-work\dist\x86_64-windows\Cabal-1.22.5.0\build > \HSBaseOh-0.1.0.0-GdNObdePATgDIW1I2OVwEc.o: unknown symbol > `initialize_parameter > s_to_default' > > -- While building package BaseOh-0.1.0.0 using: > ... > > Does somebody have some idea, what is going on? > > I am on Win 7, using stack (configured for lts-4.2) under MinGW. > (I'm using inline-c to make the bindings, and the same trick for > include - include-dirs: ... - worked fine.) > > Thanks, and sorry for the longer email. > Nicu > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > >

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CUFP 2016 Call for Presentations
by Alex Lang 18 Mar '16

18 Mar '16

Apologies for any duplicates you may receive. http://cufp.org/2016/call-for-presentations.html ====================================================================== CUFP 2016 Call for Presentations Commercial Users of Functional Programming 2016 Sponsored by SIGPLAN Co-located with ICFP 2016 Nara, Japan September 22-24 Talk Proposal Submission Deadline: 24 June 2016 CUFP 2016 Presentation Submission Form: http://goo.gl/forms/gWDSoKfizW The annual CUFP event is a place where people can see how others are using functional programming to solve real world problems; where practitioners meet and collaborate; where language designers and users can share ideas about the future of their favorite language; and where one can learn practical techniques and approaches for putting functional programming to work. ====================================================================== Giving a CUFP Talk If you have experience using functional languages in a practical setting, we invite you to submit a proposal to give a talk at the event. We're looking for two kinds of talks: Retrospective talks are typically 25 minutes long. Now that CUFP has run for more than a decade, we intend to invite past speakers to share what they’ve learned after a decade spent as commercial users of functional programming. We will favour experience reports that include technical content. Technical talks are also 25 minutes long, and should focus on teaching the audience something about a particular technique or methodology, from the point of view of someone who has seen it play out in practice. These talks could cover anything from techniques for building functional concurrent applications, to managing dynamic reconfigurations, to design recipes for using types effectively in large-scale applications. While these talks will often be based on a particular language, they should be accessible to a broad range of programmers. We strongly encourage submissions from people in communities that are underrepresented in functional programming, including but not limited to women; people of color; people in gender, sexual and romantic minorities; people with disabilities; people residing in Asia, Africa, or Latin America; and people who have never presented at a conference before. We recognize that inclusion is an important part of our mission to promote functional programming. So that CUFP can be a safe environment in which participants openly exchange ideas, we abide by the SIGPLAN Conference Anti-Harassment Policy ( http://www.sigplan.org/Resources/Policies/Anti-harassment) If you are interested in offering a talk, or nominating someone to do so, please submit your presentation before 24 June 2016 via the CUFP 2016 Presentation Submission Form (http://goo.gl/forms/gWDSoKfizW) You do not need to submit a paper, just a short proposal for your talk. There will be a short scribe's report of the presentations and discussions but not of the details of individual talks, as the meeting is intended to be more of a discussion forum than a technical interchange. Nevertheless, presentations will be recorded and presenters will be expected to sign an ACM copyright release form. Note that we will need all presenters to register for the CUFP workshop and travel to Japan at their own expense. There are some funds available to would-be presenters who require assistance in this respect. ====================================================================== Program Committee Katie Ots (Facebook), co-chair Alex Lang (Tsuru Capital), co-chair Rúnar Óli Bjarnason (Verizon Labs) Mark Hibberd (Ambiata) Mirai Ikebuchi (Nagoya University) Paul Khuong (AppNexus) Carin Meier (Cognitect) Kenji Rikitake (Kenji Rikitake Professional Engineer's Office) ====================================================================== More information For more information on CUFP, including videos of presentations from previous years, take a look at the CUFP website at http://cufp.org. Note that presenters, like other attendees, will need to register for the event. Acceptance and rejection letters will be sent out by July 15th. ====================================================================== Guidance on giving a great CUFP talk Focus on the interesting bits: Think about what will distinguish your talk, and what will engage the audience, and focus there. There are a number of places to look for those interesting bits. Setting: FP is pretty well-established in some areas, including formal verification, financial processing, and server-side web services. An unusual setting can be a source of interest. If you're deploying FP-based mobile UIs or building servers on oil rigs, then the challenges of that scenario are worth focusing on. Did FP help or hinder in adapting to the setting? Technology: The CUFP audience is hungry to learn about how FP techniques work in practice. What design patterns have you applied, and to what areas? Did you use functional reactive programming for user interfaces, or DSLs for playing chess, or fault-tolerant actors for large-scale geological data processing? Teach us something about the techniques you used, and why we should consider using them ourselves. Getting things done: How did you deal with large-scale software development in the absence of pre-existing support tools that are often expected in larger commercial environments (IDEs, coverage tools, debuggers, profilers) and without larger, proven bodies of libraries? Did you hit any brick walls that required support from the community? Don't just be a cheerleader: It's easy to write a rah-rah talk about how well FP worked for you, but CUFP is more interesting when the talks also cover what doesn't work. Even when the results were all great, you should spend more time on the challenges along the way than on the parts that went smoothly.

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Calling Haskellers to Bryn Mawr & Haverford
by Richard Eisenberg 18 Mar '16

18 Mar '16

Anyone who has probed deeply (or at all!) into the delay behind the release of GHC 8.0 may have come across protestations from me that I'm on a job search and have been struggling to find the time to finish off the last few show-stopper bugs. That search has now come to a very happy conclusion, and so I'm writing to share the news: I will be starting as an Assistant Professor at Bryn Mawr College this fall. In my role there, I'm expecting to introduce a new course (or two) on functional programming using Haskell (though the emphasis would be more on pure, strongly typed functional programming than on Haskell, per se), as well as to continue to pursue my research interests in the design and implementation of functional languages along with the requisite type theory. Undergrads will feature prominently in my research efforts, joining my research lab and collaborating on research papers. That's where you come in. Are you, reading this list, a high school student? (Or perhaps an undergrad looking for a change?) Do you know a Haskeller who is? Then come to Bryn Mawr and work with me to design the functional language of the future. "But wait!" many of you might say, "isn't Bryn Mawr only for women?" Yes, indeed it is. However, right down the street is Haverford College, a co-ed school. Haverford and Bryn Mawr share a close relationship, with regular free transportation (< 10 mins) between the schools and very frequent cross-registration for courses. Haverford students even sometimes declare their major at Bryn Mawr and vice versa. The CS departments regularly coordinate in deciding which courses to offer and when, in order to allow students to access the resources of both colleges. So, for you young men out there, I'll rephrase: Are you, reading this list, a high school student? (Or perhaps an undergrad looking for a change?) Do you know a Haskeller who is? Then come to Haverford (or Swarthmore, or University of Pennsylvania) and work with me to design the functional language of the future. I've included Swarthmore and UPenn (where I'm finishing my dissertation) above as members of the Quaker Consortium, where students have cross-registration privileges. Swarthmore is also in the Tri-College Consortium with Bryn Mawr, which also allows easier inter-college research experiences. Swarthmore students can get to Bryn Mawr via free van service (~25 mins) and UPenn students can get to Bryn Mawr via 20 minutes on SEPTA regional rail (these links are admittedly less convenient than the Haverford bus). Of course, I'm happy to answer questions. Though, being new to Bryn Mawr, I may have to refer you to others to get the answers! Hope to see you on campus! Richard

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GHC Performance Regression
by Dominic Steinitz 18 Mar '16

18 Mar '16

Some time ago I wrote a little test program for random number generation. Under 7.8.3 I get > Total time 9.03s ( 9.15s elapsed) Under 7.10.3 I get > Total time 24.773s ( 25.288s elapsed) Now of course it could be the libraries that I am using rather than GHC itself so I have tried to make them as similar as possible. For 7.8.3 I have > build-depends: base ==4.7.0.1, > mtl ==2.1.3.1, > primitive == 0.6, > mwc-random == 0.13.3.2, > vector == 0.10.12.3, > random ==1.1, > random-fu == 0.2.6.2, > random-source == 0.3.0.6 For 7.10.3 I have > build-depends: base ==4.8.2.0, > mtl ==2.2, > primitive == 0.6, > mwc-random == 0.13.3.2, > vector == 0.10.12.3, > random ==1.1, > random-fu == 0.2.6.2, > random-source == 0.3.0.6 So the only differences are in mtl and base. I don’t seem to be able to coax cabal into using mtl-2.2 for 7.8.3 with all the other required libraries. > dominic@ghcPerformance:~$ cabal install 'random-source ==0.3.0.6' 'random-fu ==0.2.6.2' 'random ==1.1' 'primitive ==0.6' 'mwc-random ==0.13.3.2' 'mtl ==2.2' 'vector ==0.10.12.3' --with-ghc=ghc-7.10.3 > Resolving dependencies... > All the requested packages are already installed: > mtl-2.2 > mwc-random-0.13.3.2 > primitive-0.6 > random-1.1 > random-fu-0.2.6.2 > random-source-0.3.0.6 > vector-0.10.12.3 > Use --reinstall if you want to reinstall anyway. > dominic@ghcPerformance:~$ cabal install 'random-source ==0.3.0.6' 'random-fu ==0.2.6.2' 'random ==1.1' 'primitive ==0.6' 'mwc-random ==0.13.3.2' 'mtl ==2.2' 'vector ==0.10.12.3' --with-ghc=ghc-7.8.3 > Resolving dependencies... > cabal: Could not resolve dependencies: > trying: random-source-0.3.0.6/installed-70e... (user goal) > next goal: mtl (user goal) > rejecting: mtl-2.2.1, 2.2.0.1 (global constraint requires ==2.2) > rejecting: mtl-2.2/installed-cc5..., 2.2 (conflict: random-source => > mtl==2.1.3.1/installed-8bc...) > rejecting: mtl-2.1.3.1/installed-8bc..., 2.1.3.1, 2.1.2, 2.1.1, 2.1, 2.0.1.1, > 2.0.1.0, 2.0.0.0, 1.1.1.1, 1.1.1.0, 1.1.0.2, 1.1.0.1, 1.1.0.0, 1.0 (global > constraint requires ==2.2) > Backjump limit reached (change with --max-backjumps). Cabal seems to be telling me that random-source-0.3.0.6 is the problem but if I look at the constraints for that package here https://hackage.haskell.org/package/random-source <https://hackage.haskell.org/package/random-source> then I see > mtl <https://hackage.haskell.org/package/mtl> (>=1 && <3) I am not sure how to proceed from here. Should I raise an issue on the GHC bug tracker? I’d like to solve this myself but I don’t want to start building versions of ghc to see which change caused the regression without first eliminating mtl. Any ideas would be gratefully received. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com > {-# LANGUAGE TemplateHaskell #-} > {-# LANGUAGE GADTs #-} > {-# LANGUAGE FlexibleInstances #-} > > import Data.Random > import Data.Random.Source > import qualified System.Random.MWC as MWC > import Control.Monad.Reader > import Control.Monad.Primitive > > $(monadRandom [d| > instance (PrimMonad m, s ~ PrimState m) => MonadRandom (ReaderT (MWC.Gen s) m) where > getRandomWord16 = ask >>= lift . MWC.uniform > getRandomWord32 = ask >>= lift . MWC.uniform > getRandomWord64 = ask >>= lift . MWC.uniform > |]) > > testUniform :: MonadRandom m => Int -> m [Double] > testUniform n = replicateM (fromIntegral n) (sample stdUniform) > > n :: Int > n = 10^7 > > main :: IO () > main = do > seed <- MWC.create > xs <- runReaderT (testUniform n) seed > print (sum xs / fromIntegral n) This cabal file will build this on 7.8.3 > name: PerfTest8 > version: 0.1.0.0 > homepage: TBD > license: MIT > author: Dominic Steinitz > maintainer: idontgetoutmuch(a)gmail.com > category: System > build-type: Simple > cabal-version: >=1.10 > > executable Random8 > main-is: TestMwcViaRandomSource.hs > build-depends: base ==4.7.0.1, > mtl ==2.1.3.1, > primitive == 0.6, > mwc-random == 0.13.3.2, > vector == 0.10.12.3, > random ==1.1, > random-fu == 0.2.6.2, > random-source == 0.3.0.6 > default-language: Haskell2010 This cabal file will build this on 7.10.3 > name: PerfTest10 > version: 0.1.0.0 > homepage: TBD > license: MIT > author: Dominic Steinitz > maintainer: idontgetoutmuch(a)gmail.com > category: System > build-type: Simple > cabal-version: >=1.10 > > executable Random10 > main-is: TestMwcViaRandomSource.hs > build-depends: base ==4.8.2.0, > mtl ==2.2, > primitive == 0.6, > mwc-random == 0.13.3.2, > vector == 0.10.12.3, > random ==1.1, > random-fu == 0.2.6.2, > random-source == 0.3.0.6 > default-language: Haskell2010

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Trying desperately to make a c library binding on Windows
by Nicu Ionita 17 Mar '16

17 Mar '16

Hi all, I am really stuck with my try to make a Haskell binding for the library bayesopt on Windows. In theory it looks all simple, just put some lines in the cabal configuration file: ... extra-lib-dirs: /path/to/the/lib -- contains the file libbayesopt.a extra-libraries: bayesopt ... But whatever I tried, I can't step over the configuration phase, coz I get (I'm compiling with stack): Configuring BaseOh-0.1.0.0... setup-Simple-Cabal-1.22.5.0-x86_64-windows-ghc-7.10.3.exe: Missing dependency on a foreign library: * Missing C library: /j/BO/lib/libbayesopt.a This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. If I comment those lines out, then the configure phase succeeds, the library is compiled (i.e. my binding library), but a test executable in the same project does of course not compile, as symbols are missing: ... In-place registering BaseOh-0.1.0.0... Preprocessing executable 'test' for BaseOh-0.1.0.0... [1 of 2] Compiling Optimisation.Stochastic.BayesOpt ( src\Optimisation\Stochasti c\BayesOpt.hs, .stack-work\dist\x86_64-windows\Cabal-1.22.5.0\build\test\test-tm p\Optimisation\Stochastic\BayesOpt.o ) ghc.exe: unable to load package `BaseOh-0.1.0.0' ghc.exe: J:\Projects\BaseOh\.stack-work\dist\x86_64-windows\Cabal-1.22.5.0\build \HSBaseOh-0.1.0.0-GdNObdePATgDIW1I2OVwEc.o: unknown symbol `initialize_parameter s_to_default' -- While building package BaseOh-0.1.0.0 using: ... Does somebody have some idea, what is going on? I am on Win 7, using stack (configured for lts-4.2) under MinGW. (I'm using inline-c to make the bindings, and the same trick for include - include-dirs: ... - worked fine.) Thanks, and sorry for the longer email. Nicu

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Prelude.head: empty list
by Han Joosten 17 Mar '16

17 Mar '16

In a rather large program I made some changes, and now I get the runtime error: ampersand.exe: Prelude.head: empty list Of course I know that head is partial, and should be used with care. It is used many times (we have 100+ modules in the program). Is there an elegant way to get some information about where the specific call to head is being made? Thanks!

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Re: [Haskell-cafe] Link error
by Alexander Altman 17 Mar '16

17 Mar '16

This is actually nothing at all to do with formatting; instead it’s what’s known as Z-encoding: see https://ghc.haskell.org/trac/ghc/wiki/Commentary/Compiler/SymbolNames for details. > > > EmbedTree_zdfLiftEntryzuzdclift_closure > > > I've seen something like this before -- I think the 'zd' and 'zu' in there > are supposed to be formatting tokens, %zd and %zu, for architecture-aware > data sizing. I ran into this while building the Haskell GTK bindings on > Windows, and IIRC it was caused by GHC 7.8 bundling an older GCC. >

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Re: [Haskell-cafe] Link error
by Theodore Lief Gannon 17 Mar '16

17 Mar '16

>EmbedTree_zdfLiftEntryzuzdclift_closure I've seen something like this before -- I think the 'zd' and 'zu' in there are supposed to be formatting tokens, %zd and %zu, for architecture-aware data sizing. I ran into this while building the Haskell GTK bindings on Windows, and IIRC it was caused by GHC 7.8 bundling an older GCC.

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Link error
by fr33domlover 16 Mar '16

16 Mar '16

Hello, I'm getting this when trying to build the tests of the 'ssh' package: -------------------------------------------------------------------- ssh-0.3.2: build (lib + test) Preprocessing library ssh-0.3.2... In-place registering ssh-0.3.2... Preprocessing test suite 'ssh-test' for ssh-0.3.2... [2 of 2] Compiling Main ( test/test.hs, .stack-work/dist/x86_64-linux/Cabal-1.22.5.0/build/ssh-test/ssh-test-tmp/Main.o ) /usr/bin/ld: .stack-work/dist/x86_64-linux/Cabal-1.22.5.0/build/ssh-test/ssh-test-tmp/EmbedTree.dyn_o: relocation R_X86_64_PC32 against symbol `EmbedTree_zdfLiftEntryzuzdclift_closure' can not be used when making a shared object; recompile with -fPIC /usr/bin/ld: final link failed: Bad value collect2: error: ld returned 1 exit status Progress: 1/2 -- While building package ssh-0.3.2 using: /home/fr33domlover/.stack/setup-exe-cache/x86_64-linux/setup-Simple-Cabal-1.22.5.0-ghc-7.10.3 --builddir=.stack-work/dist/x86_64-linux/Cabal-1.22.5.0 build lib:ssh test:ssh-test --ghc-options " -ddump-hi -ddump-to-file" Process exited with code: ExitFailure 1 -------------------------------------------------------------------- Other people don't get this error. What does it mean, how do I start to debug and fix it? Thanks in advance for any clue! --fr33

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GHCi on Pi Zero
by alex 16 Mar '16

16 Mar '16

Hi all, I'm struggling with getting a working ghci on the Raspberry Pi Zero. I managed to get a ghc with ghci installed via jessie-backports, but when I run ghci from the commandline I simply get a "Illegal instruction" message. Has anyone had more luck, or does anyone have ideas / tips? Best wishes alex -- http://yaxu.org/

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Zoom instance for Coroutine
by Konstantin Saveljev 14 Mar '16

14 Mar '16

Hello, I am using monad-coroutine <https://hackage.haskell.org/package/monad-coroutine> package and have something like Coroutine (Await Int) (State MyState) Int (simplified version, for example purpose). MyState is deeply nested and I do a lot of modifications in it. Previously (with different data types) I was able to use zoom from lens <https://hackage.haskell.org/package/lens>in order to simplify the typing/view of code which operates on some subtree of the state, e.g.: zoom (company.assets) $ do something.a = someComputation anotherthing.b = False this.that = "someString" The problem I am having is that I cannot come up with instance Zoom for the Coroutine and was wondering if anyone is able to help me with that? Best regards, Konstantin

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Foldable/Traversable and Applicative/Monoid?
by David Banas 14 Mar '16

14 Mar '16

Hi all, I don't understand why Foldable is a necessary super-class of Traversable, and I suspect that the Applicative/Monoid duality, which I've just begun discovering in the literature, has something to do with why that is so. Can anyone give me a hint, without giving me the answer? Thanks! -db

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ANN: katip - a new structured logging framework for Haskell
by Ozgun Ataman 14 Mar '16

14 Mar '16

Fellow Haskellers, We're delighted to release a new logging framework today called "katip", centered around the idea of making it easy to include contextual data in individual log items in the form of structured fields. Katip has become, rather quickly, our go-to logging library at Soostone, included in everything from simple ad-hoc scripts to production systems under load. You can find katip on both Hackage[1] and Github[2]. The core library has also been added to Stackage nightly, though the ElasticSearch backend is waiting on a dependency conflict on aeson. We hope you find it useful and look forward to any contributions or feedback! [1] http://hackage.haskell.org/package/katip [2] https://github.com/Soostone/katip As a little summary, here's the features checklist from the README: * *Structured:* Logs are structured, meaning they can be individually tagged with key value data (JSON Objects). This helps you add critical details to log messages before you need them so that when you do, they are available. Katip exposes a typeclass for log payloads so that you can use rich, domain-specific Haskell types to add context that will be automatically merged in with existing log context. * *Easy to Integration:* Katip was designed to be easily integrated into existing monads. By using typeclasses for logging facilities, individual subsystems and even libraries can easily add their own namespacing and context without having any knowledge of their logging environment. * *Practical Use:* Katip comes with a set of convenience facilities built-in, so it can be used without much headache even in small projects. * A `Handle` backend for logging to files in simple settings. * A `AnyLogPayload` key-value type that makes it easy to log structured columns on the fly without having to define new data types. * A `Monadic` interface where logging namespace can be obtained from the monad context. * Multiple variants of the fundamental logging functions for optionally including fields and line-number information. * *Extensible:* Can be easily extended (even at runtime) to output to multiple backends at once (known as scribes). See `katip-elasticsearch` as an example. Backends for other forms of storage are trivial to write, including both hosted database systems and SaaS logging providers. * *Debug-Friendly:* Critical details for monitoring production systems such as host, PID, thread id, module and line location are automatically captured. User-specified attributes such as environment (e.g. Production, Test, Dev) and system name are also captured. * *Configurable:* Can be adjusted on a per-scribe basis both with verbosity and severity. * *Verbosity* dictates how much of the log structure should actually get logged. In code you can capture highly detailed metadata and decide how much of that gets emitted to each backend. * *Severity* AKA "log level" is specified with each message and individual scribes can decide whether or not to record that severity. It is even possible to at runtime swap out and replace loggers, allowing for swapping in verbose debug logging at runtime if you want. * *Battle-Tested:* Katip has been integrated into several production systems since 2015 and has logged hundreds of millions of messages to files and ElasticSearch.

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ANNOUNCE: Frown, Ralf Hinze's LALR(k) parser generator for Haskell, now slightly upkept ☺
by M Farkas-Dyck 13 Mar '16

13 Mar '16

Some years ago, Ralf Hinze wrote this parser generator [0], and i have since been using it, so i cleaned it up and uploaded it to Hackage as "frown" [1]. My repo is here: https://github.com/strake/frown [0] http://www.cs.ox.ac.uk/ralf.hinze/frown/ [1] https://hackage.haskell.org/package/frown

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Module name to package name index
by Harendra Kumar 13 Mar '16

13 Mar '16

Is there something available which can answer questions like this - what all packages on Hackage export "Data.List" module? Another useful question could be - what all packages export symbol named 'x'? Hackage search or hoogle are not helpful in providing a precise answer to these. I am assuming that related functionality usually lands up in the same part of the module namespace. This fact can help us in discovering related or alternative packages or functions available in a given area. For example when I am looking for list related functions I can search for who all exports "Data.List". I guess creating such an index should not be difficult. All the necessary information is available in the packages' .cabal files, we just need to extract it and create a module name to package name index. -harendra

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