June 2016 - Haskell-Cafe

partial solved problem installing postgreSQL-libpq on Windows?
by Kees Bleijenberg 16 Jun '16

16 Jun '16

Maybe I've found a part of the solution. I changed in postgresql-libpq.cabal Extra-Libraries: from pq to libpq. Then runHaskell xx configure -ghc, runHaskell xx build and then runHaskell xx install. No errors.. I'am happy. But. if I try to install postgresql-simple or hasql I get this error : .. <command line>: can't load .so/.DLL for: d:/PROGRA~2/POSTGR~1/9.3/lib\libpq.dll (addDLL: could not load DLL) ghc.exe: d:/PROGRA~2/POSTGR~1/9.3/lib\libpq: %1 is not a valid Win32 application. ... dir d:\PROGRA~2\POSTGR~1\9.3\lib\libpq.dll finds the dll, but d:/PROGRA~2/POSTGR~1/9.3/lib/libpq.dll gives: 'Parameter format not correct'. These mangled filenames come from pg_config.exe. Is this a filename mangling problem? Any idea what is going on? Kees --------------------------- I want to install postgreSQL-libpq on Windows 7 64 bits with ghc version 7.10.1 and cabal version 1.22.4.0 This is what I did: Installed mingw >From the msys prompt: pexports "d:\program files\postgreSQL\9.3\bin\libpq.dll" > libpq.def >From the msys prompt: dlltool -d libpq.def -l libpq.a The file libpq.a is created. I copied the file to d:\program files\postgreSQL\9.3\bin\ and then from de cmd prompt: cabal install postgreSQL-libpq --extra-include-dirs="d:\program files\postgreSQL\9.3\include" --extra-lib-dirs="d:\program files\postgreSQl\9.3\bin" I get: Resolving dependencies... Configuring postgresql-libpq-0.9.1.1... Failed to install postgresql-libpq-0.9.1.1 Build log ( C:\Users\kees\AppData\Roaming\cabal\logs\postgresql-libpq-0.9.1.1.log ): [1 of 1] Compiling Main ( D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.hs, D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\Main.o ) Linking D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.exe ... Configuring postgresql-libpq-0.9.1.1... setup.exe: Missing dependency on a foreign library: * Missing C library: pq 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. What can I do? Kees

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problem installing postgreSQL-libpq on Windows
by Kees Bleijenberg 16 Jun '16

16 Jun '16

I want to install postgreSQL-libpq on Windows 7 64 bits with ghc version 7.10.1 and cabal version 1.22.4.0 This is what I did: Installed mingw >From the msys prompt: pexports "d:\program files\postgreSQL\9.3\bin\libpq.dll" > libpq.def >From the msys prompt: dlltool -d libpq.def -l libpq.a The file libpq.a is created. I copied the file to d:\program files\postgreSQL\9.3\bin\ and then from de cmd prompt: cabal install postgreSQL-libpq --extra-include-dirs="d:\program files\postgreSQL\9.3\include" --extra-lib-dirs="d:\program files\postgreSQl\9.3\bin" I get: Resolving dependencies... Configuring postgresql-libpq-0.9.1.1... Failed to install postgresql-libpq-0.9.1.1 Build log ( C:\Users\kees\AppData\Roaming\cabal\logs\postgresql-libpq-0.9.1.1.log ): [1 of 1] Compiling Main ( D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.hs, D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\Main.o ) Linking D:\Temp\cabal-tmp-6140\postgresql-libpq-0.9.1.1\dist\setup\setup.exe ... Configuring postgresql-libpq-0.9.1.1... setup.exe: Missing dependency on a foreign library: * Missing C library: pq 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. What can I do? Kees

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This non-exhaustive pattern match seems exhaustive
by Mitchell Rosen 15 Jun '16

15 Jun '16

I'm emulating a "closed typeclass" using a closed type family: * {-# LANGUAGE ExistentialQuantification #-}* * {-# LANGUAGE GADTs #-}* * {-# LANGUAGE LambdaCase #-}* * {-# LANGUAGE TypeFamilies #-}* * import GHC.Exts (Constraint)* * -- This is like* * --* * -- class Thing a -- instance Thing Int --* * type family Thing a :: Constraint where* * Thing Int = ()* * data Foo = forall a. Thing a => Foo (Bar a)* * data Bar a where* * Bar1 :: Bar Int* * Bar2 :: Bar Bool* * inspectFoo :: Foo -> ()* * inspectFoo = \case* * Foo Bar1 -> ()* * Foo Bar2 -> () -- This is required to suppress a warning* Here, it's not possible to create a Foo using "Foo Bar2", because there is no "Thing Bool" constraint in scope. Yet, when picking apart a Foo, I must still pattern match on this impossible data. Is there some smarter way to write this code? I thought of using `constraints`, and adding a catch-all clause to Thing: * type family Thing a :: Constraint where Thing Int = ()* * Thing a = Bottom* This would at least allow users of a Foo to use some * absurd :: Bottom => a* thing to discharge the Bottom constraint brought in scope by pattern matching: * inspectFoo :: Foo -> () inspectFoo = \case Foo Bar1 -> () Foo Bar2 -> absurd bottom* but better still would be to avoid having to write these impossible cases. Thanks!

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benchmarks game -- invalid Haskell fasta programs
by Isaac Gouy 15 Jun '16

15 Jun '16

The guidelines for the benchmarks game "fasta" programs changed to: -- "match a random number against those cumulative probabilities to select each nucleotide (use linear search or binary search)". I'd appreciate it if someone familiar with Haskell could confirm that the old Haskell programs are not compatible with the changed guidelines. Here are those old programs: http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… http://benchmarksgame.alioth.debian.org/u64q/program.php?test=fasta&lang=gh… best wishes, Isaac

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Help with Data.Conduit.List.mapAccum
by bruno＠ruomad.net 15 Jun '16

15 Jun '16

Hello, I'm trying to use Data.Conduit, but I get stuck with mapAccum as how to get and retrieve the result. If I use it, I get a simple conduit like : testC :: ConduitM () Int IO Int testC = Src =$= cdt where src = CL.sourceList [1..10] cdt = CL.mapAccum (\x s ->(x+s, x) 0 I can get the output with testC $$ CL.consume but how do I retrieve the accumulated sum ? Bruno

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ANN: eccrypto, aka Hecc, hF2
by Marcel Fourné 15 Jun '16

15 Jun '16

Dear Haskell Community! It was a long~ish time ago I released hecc[1], which had an unfortunate but funny (to me) name, later together with hF2[2]. Since I have neither released hyperelliptic curve crypto support, nor my pairing based crypto, a generalising change in names would be in order. Today I am releasing eccrypto[3], which contains the code of both (to allow easier refactoring of new ideas) and something new: A pure Haskell, timing-attack resistant Ed25519[4] implementation! ...well, a very rough one at least. The code is not "done", gives wrong results, is _very_ slow, but it might serve as reading material as well as a primer what I plan to do in the future. I do not plan to add embedded C or assembler code, but plan to make the code comparatively fast to some common implementations as well as timing attack resistant (see: [5]), even if it will never be as fast as the best code used in contemporary benchmarks. Sadly, due to health issues, I am not able to work on said code and have not been for a time longer than I care to admit. All comments are welcome, but I will not be able to guarantee answers. ;) Best of wishes to a thriving community, Marcel Fourné [1]: https://hackage.haskell.org/package/hecc [2]: https://hackage.haskell.org/package/hF2 [3]: https://hackage.haskell.org/package/eccrypto [4]: https://ed25519.cr.yp.to/ [5]: https://mail.haskell.org/pipermail/haskell-cafe/2015-February/118213.html

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[ANN] Budapest Haskell Hackathon 2016, 6-7th Aug 2016
by Gmail 15 Jun '16

15 Jun '16

Hi everybody, I'm happy to announce that our local user group will hold a Haskell Hackathon in Budapest this year (this will be the second)! We will hold it from August 6th to the 7th (Saturday & Sunday). You can find out more on the following link: https://wiki.haskell.org/Budapest_Hackathon_2016 We will reguraly update the site with new information. If you decide to come, please fill out the following Google Form: http://goo.gl/forms/pqgh6fvK8F8a2pAg1 If you have a project, demo, or talk that you want to bring to the event please contact us, and we can talk about the details. You can find our contact info the events wiki site, or you can just contact me directly. The event will be open to people of all experience levels, from beginners to gurus. The only requisite is that you’re interested in the Haskell language, and want to hang out with us, and have a good time! Greetings from Daniel, and the other BP-HUG organizers.

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2nd Call for Papers: OCL and Textual Modeling Tools and Textual Model Transformations (OCL 2016) - Submit Your Paper Until July 17, 2016
by Achim D. Brucker 14 Jun '16

14 Jun '16

(Apologies for duplicates) Only four weeks until the deadline! -- Dr. Achim D. Brucker | Senior Lecturer | University of Sheffield https://www.brucker.ch/

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Package takeover (also: the future of Netwire)
by esz＠posteo.de 14 Jun '16

14 Jun '16

Hi everybody, I'd like to take over the following Hackage packages with my account named [esz]: * acme-schoenfinkel, * cascading, * continue, * contstuff-monads-tf, * contstuff-transformers, * contstuff, * dnscache, * fastirc, * ihttp, * instinct, * ismtp, * netlines, * netwire, * quickset, * web-page, * webwire, * yesod-tableview. These are actually already mine, but because my old account has become practically inaccessible, I'm now following the official [takeover procedure], asking myself whether I'm okay with that. =) After the takeover, I'm going to deprecate the following packages, unless someone would like to take over maintenance: * cascading: Clay is more comprehensive and easier to use. * contstuff*: Childhood experiments, because after writing a monad tutorial of course you must write an mtl replacement. * dnscache: Useful library, but needs maintenance. * fastirc: irc is reasonably efficient now (it used to be a String parser). * ihttp: use http-client. * ismtp: Useful library, but needs maintenance and should be rewritten using a modern streaming library. * netlines: use a modern streaming library. * netwire: Useful library, but needs maintenance and has high maintenance cost due to its design. I'll likely replace it by a new abstraction at some point, using a different package name. Currently I recommend using one of the following libraries for FRP: * reactive-banana: My former favourite when it comes to push/pull FRP. Well designed, clean semantics, reasonably efficient. * reflex: My current favourite when it comes to push/pull FRP. Well designed, clean semantics, reasonably efficient. * Yampa: AFRP for games, simulations and other real-time applications (for when a high and predictable framerate is more important than pushed events, same target domain as Netwire). * webwire: Experiment with FRP for handling server-side sessions in web applications. Works with some caveats, not that useful in practice. * yesod-tableview: needs maintenance, not that useful in modern web applications. That leaves the following packages for active maintenance by me, which includes making sure they compile, keeping them free of bugs and verifying/applying contributions. Most of these need maintenance right now: * acme-schoenfinkel: Surprisingly useful joke package. Needs a few adjustments to compile with modern GHC. * continue: Monad transformer for named reentry points, isomorphic to CofreeT. Ideally this should be just an interface to CofreeT from 'free', but unfortunately that one's instances are more restrictive than necessary (Alternative instead of Plus), making it useless. You couldn't use reasonable data structures like HashMap or Map. * instinct: Efficient feed-forward neural networks with backprop learning. To be replaced by a more general machine learning framework at some point, but still useful on its own. Needs maintenance. * quickset: Compact query-only binary search arrays. Needs a more comprehensive API. * web-page: Component system for web pages. Needs a more general API, because currently it makes too many assumptions on which packages you use (blaze-html, clay and jmacro). Note: do not confuse with Athan Clark's 'webpage' library. [esz]: https://hackage.haskell.org/user/esz [takeover procedure]: https://wiki.haskell.org/Taking_over_a_package Greets, Ertugrul

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Reminder: 10 days to submit talks to CUFP 2016
by Alex Lang 14 Jun '16

14 Jun '16

This CFP and the form for submitting presentation proposals can be found at: http://cufp.org/2016/call-for-presentations.html ---------------------------------------------------------------------- 2016 Call for Presentations Workshop for Commercial Users of Functional Programming 2016 Sponsored by SIGPLAN CUFP 2016 Co-located with ICFP 2016 Nara, Japan September 22-24 Talk Proposal Submission Deadline: 24 June 2016 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. 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 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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