June 2016 - Haskell-Cafe

CUFP 2016 Call For Tutorials
by Román González 14 Jun '16

14 Jun '16

Hi all, The Commercial Users of Functional Programming (CUFP) 2016 has its Call for Tutorials open for submission. CUFP 2016 is being held in the historic city of Nara, Japan. The conference is devoted to showcase the state of the art of Functional Programming on industrial settings. This conference is co-located with the International Conference of Functional Programming (ICFP). We're looking for tutors that would like to host workshops on on the following themes: - Introductions to functional programming languages. In the past we have had sessions of Clojure, Erlang, F#, F*, Haskell, ML, OCaml, Scala, Scheme and others. - Advanced programming languages, concepts and applications (e.g. Lens, Liquid-Haskell, Agda, Idris, etc.) - Applying functional programming in particular areas, including Web, high-performance computing, finance. - Tools and techniques supporting state of the art functional programming. In the past we have had tutorials on QuickCheck, Elm and others. - Theory. Type theory, category theory, abstract algebra, ongoing or new research, and anything useful or interesting to functional programmers. If you'd like to submit a proposal, just fill this form http://goo.gl/forms/qoyK9qYPZhiDPSzO2. More info can be found at http://cufp.org/2016/call-for-tutorials.html Regards, Roman Gonzalez.

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[ANN] aivika-lattice-0.1
by David Sorokin 12 Jun '16

12 Jun '16

Hi Cafe, I’m glad to introduce a complete new module aivika-lattice [1] for the Aivika simulation library. It allows running nested discrete event simulations within lattice. If the naive approach implies that traversing the nested simulation nodes has an exponential complexity, then the lattice approach gives us a quadratical growth. This is a key feature, which makes the traversing a computationally feasible task even for a large size lattice. It can be useful for financial modeling, for instance. The model can be divided into two different parts. The first part is a discrete event simulation that branches in the lattice nodes. Within this simulation, we can update a mutable reference that can be observed in another part of the model. For example, such a reference can store a value of the modeled interest rate, or stock price, or exchange rate. It is important that the first part is forward traversing, when the time increases from the past to the future. The first part can even include discontinuous processes, resources, queues, streams of transacts if required. This is a general purpose simulation library. The second part is quite opposite. This is an estimating part. It is backward-traversing, where we estimate the past based on estimations of the future. When estimating, we can observe the mutable reference values. This is a bridge for connecting two different parts of the model. For example, we can estimate the price of the contract by the model of interest and exchange rates specified in the first part of the model. The package is quite experimental. It is mainly a proof of concept. There was no goal to achieve the highest possible speed of simulation, which is important for such tasks. Best regards, David Sorokin [1] http://hackage.haskell.org/package/aivika-lattice

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left to right pipeline of functions
by Christopher Howard 12 Jun '16

12 Jun '16

Hi, I am learning about monads, and this question came to mind: is there a way to have a sequence of functions left to right like so: g = return 2 >>= \n -> return (n + 1) >>= \n -> return (n + 3) Either: some kind of generic monad that makes this legal, or some way to do this without monad (i.e., without the "returns"). -- http://justonemoremathproblem.com To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

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All-fail case in asum
by Юрий Сыровецкий (Yuriy Syrovetskiy) 11 Jun '16

11 Jun '16

Hello I want to define some parser such way: myParser = tryA <|> tryB <|> fail "input must be either A or B" It works. But then I want to rewrite it with asum: myParser = asum [tryA, tryB, fail "must be A or B"] It works, but the wrong way. Instead of my error it writes "empty". Just "empty". It is so because in base library asum = foldr (<|>) empty What if it was defined asum [] = empty asum [x:xs] = x <|> asum xs It would help me with my parser. But what can this break? Why isn't this done yet? -- Yuriy Syrovetskiy, http://cblp.su

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Call pattern specialization limit messages
by David Feuer 11 Jun '16

11 Jun '16

When I compile Data.Sequence with -dppr-debug, I get several messages about constructor specialization exceeding the call pattern limit. Things like SpecConstr Function ‘$j_ssfy{v} [lid]’ has four call patterns, but the limit is 3 Use -fspec-constr-count=n to set the bound Specialisations: [([sc_sAZr{v} [lid]], [sc_sAZr{v} [lid], lvl_sdmH{v} [lid]]), ([sc_sAZs{v} [lid]], [sc_sAZs{v} [lid], lvl_sw9X{v} [lid]]), ([sc_sAZt{v} [lid]], [sc_sAZt{v} [lid], lvl_swa0{v} [lid]]), ([sc_sAZu{v} [lid]], [sc_sAZu{v} [lid], lvl_swat{v} [lid]])] How can I figure out what function this sort of thing is actually talking about? I'd love to see what benchmarks say about whether tweaking -fspec-constr-count is a good idea, but I don't know what to benchmark. Thanks, David

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Re: [Haskell-cafe] All-fail case in asum
by David Feuer 10 Jun '16

10 Jun '16

Or, to keep it a fold, asum xs = foldr go (fromMaybe empty) xs Nothing where go x r Nothing = r (Just x) go x r (Just prev) = prev <|> r (Just x) On Jun 10, 2016 11:09 AM, "Dan Burton" <danburton.email(a)gmail.com> wrote: Add a pattern match for the single-element list to stop it from hitting the empty list base case. asum [] = empty asum [x] = x asum (x:xs) = x <|> asum xs On Friday, June 10, 2016, Tom Ellis < tom-lists-haskell-cafe-2013(a)jaguarpaw.co.uk> wrote: > On Fri, Jun 10, 2016 at 05:37:41PM +0300, Юрий Сыровецкий (Yuriy > Syrovetskiy) wrote: > > It is so because in base library > > > > asum = foldr (<|>) empty > > > > What if it was defined > > > > asum [] = empty > > asum [x:xs] = x <|> asum xs > > Those are the same (assuming you mean (x:xs) instead of [x:xs]). > > Tom > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > -- -- Dan Burton _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe

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GHC 8 + ImpredictiveTypes + $
by Brendan Hay 10 Jun '16

10 Jun '16

Hi, I have had a number of trivial compilation failures in many of my projects that contain instances for MonadBaseControl (from monad-control) since upgrading to GHC 8. Now, I say 'trivial' since the actual fix is incredibly minor - a change of compose (.) to apply ($). What was less trivial was the (additional) hair loss arriving at the fix. I've put together a minimal example that demonstrates both the failing (pre-GHC8) and the fixed (GHC8) instances here: https://gist.github.com/brendanhay/e6f2501c15ac5160ca7dbb6ada6777f0 Since I found the error message somewhat directionless, I'd like some help actually understanding the root cause and why the 'fix' works: * I assume previously GHC did not fully check type aliases that were impredictive prior to GHC 8? * What does this imply for a type alias such as for the alias RunInBase used in monad-control that contains RankNTypes: http://hackage.haskell.org/package/monad-control-1.0.1.0/docs/Control-Monad… - Is such an alias not safe in some sense? (Was it never safe?) * How does the use of ($) vs (.) fix this particular issue? (I'd naively assume the usage here would be equivalent.) I recall reading about ($)'s magical type alias somewhere - is this related? Cheers, Brendan

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couldn't match expected type ByteString with actual type IO ByteString
by Carl Petersen 09 Jun '16

09 Jun '16

Hello All, I'm getting the following error: /apps/workspace/hade/src/Step/ReadExcel.hs:39:23: Couldn't match expected type ‘L.ByteString’ with actual type ‘IO L.ByteString’ In the first argument of ‘IBuf’, namely ‘j’ In the second argument of ‘sendChan’, namely ‘(IBuf j)’ when I compile the following code: data Buf = IChan (SendPort Buf) | IBuf (L.ByteString) deriving (Show,Generic,Typeable) instance Binary Buf readExcel :: Process() readExcel = do sendChan chan (IBuf j) where IChan chan = expect j = do r <- toTableRowsFromFile 8 "final-project.xlsx" let b = A.encode r return b remotable ['readExcel] Any ideas as to what I'm doing wrong? Carl

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FHPC'16 - deadline extension to 14th June
by David Duke 09 Jun '16

09 Jun '16

Dear colleagues, Following several requests for an extension, the submission deadline for FHPC'16 has been extended by 5 days to 15th June. ====================================================================== 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: Wednesday, 15 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: Wednesday 15 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 --- David Duke T: +44 113 3436800 Professor of Computer Science E: D.J.Duke(a)leeds.ac.uk Head, School of Computing W: www.comp.leeds.ac.uk/scsdjd/ PA: Gaynor Butterwick, E: G.Butterwick(a)leeds.ac.uk T: +44 113 3435767

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Haskell in Leipzig 2016: Second Call for Papers
by Joachim Breitner 09 Jun '16

09 Jun '16

Haskell in Leipzig September 14-15, 2016 HTKW Leipzig, Germany http://hal2016.haskell.org/ Allow me to remind everyone of the opportunity to talk about your research, projects or ideas at this year’s Haskell in Leipzig. The deadline is three weeks from now. == News == Unsure about whether HaL is interesting to you? No need to worry: Alejandro Russo (from Chalmers) is our keynote speaker and will talk about his work on information-flow control (i.e. SecLib, LIO, MAC, HLIO) – a great topic that is of interest to researchers, practitioners and beginners alike. == About HaL == The workshop series “Haskell in Leipzig”, now in its 11th year, brings together Haskell developers, Haskell researchers, Haskell enthusiasts and Haskell beginners to listen to talks, take part in tutorials, and join in interesting conversations. Everything related to Haskell is on topic, whether it is about current research, practical applications, interesting ideas off the beaten track, education, or art, and topics may extend to functional programming in general and its connections to other programming paradigms as well. This year, HaL is colocated with two related conferences, * the Workshop on Functional and (Constraint) Logic Programming (WFLP) and * the Workshop on (Constraint) Logic Programming (WLP), to form the Leipzig Week of Declarative Programming (L-DEC): http://nfa.imn.htwk-leipzig.de/LDEC2016/ In order to accommodate and welcome a more international audience, this year’s HaL will be held in English. == Submissions == Contributions can take the form of * talks (about 30 minutes), * tutorials (about 90 minutes), * demonstrations, artistic performances, or other extraordinary things. Please submit an abstract that describes the content and form of your presentation, the intended audience, and required previous knowledge. We recommend a length of 2 pages, so that the PC and the audience get a good idea of your submission, but this is not a hard requirement. You can submit your abstract, as an PDF document, at https://easychair.org/conferences/?conf=hal2016 until Friday, July 1, 2016. You will be notified by July 15, 2016. == Program committee == * Andreas Abel, Chalmers and Gothenburg University, Sweden * Heinrich Apfelmus, Leipzig, Germany * Joachim Breitner, Karlsruhe Institute of Technology, Germany (Chair) * Matthias Fischmann, Zerobuzz, Germany * Petra Hofstedt, BTU Cottbus-Senftenberg, Germany * Wolfgang Jeltsch, Institute of Cybernetics at Tallinn University of Technology, Estonia * Andres Löh, Well-Typed LLP, Germany * Alejandro Serrano Mena, Universiteit Utrecht, Netherlands * Neil Mitchell, Standard Chartered Bank, UK * Katie Ots, Facebook, UK * Peter Stadler, University of Leipzig, Germany * Henning Thielemann, Freelancer, Germany * Niki Vazou, University of California, San Diego, USA If you have any questions, please do not hesitate to contact Joachim Breitner <breitner(a)kit.edu>. -- Dr. rer. nat. Joachim Breitner Wissenschaftlicher Mitarbeiter http://pp.ipd.kit.edu/~breitner

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