- Haskell-Cafe - Haskell.org

help with glfw seg-fault
by briand＠aracnet.com 29 May '15

29 May '15

Hi, GLFW.swapBuffers w is the culprit. Not sure where to go from there. That's a pretty low level failure. Any suggestions. Brian

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Type inference doesn't always calculate the most generic type?
by Christophe Delord 28 May '15

28 May '15

Hello, I'm new here. Sorry if this question has already been asked. I have noticed something strange about type inference. Prelude> :t abs abs :: Num a => a -> a Prelude> let mapabs = map abs Prelude> :t mapabs mapabs :: [Integer] -> [Integer] Prelude> :t (map abs) (map abs) :: Num b => [b] -> [b] I think that "mapabs" and "map abs" should have the same generic type. In a program I can force the type like this: mapabs = map abs mapabs' :: (Num a) => [a] -> [a] mapabs' = map abs but mapabs still have the type [Integer] -> [Integer] Are there any reason for this? Regards, Christophe Delord.

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(Why) must this function remain nameless?
by Clinton Mead 28 May '15

28 May '15

The following code (somewhat contrived) code compiles on GHC without issue, and towards the end repeatedly uses the lambda function "(\fn (D x) -> f fn x)". But when I simply try to give it a name, like so: h = (\fn (D x) -> f fn x) I then get a compile error. How can I name this function, or must it remain forever nameless? ( Ideone link: http://ideone.com/mtuYnK ) --- {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE UndecidableInstances #-} {-# LANGUAGE OverlappingInstances #-} {-# LANGUAGE ScopedTypeVariables #-} {-# LANGUAGE ExistentialQuantification #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE ConstraintKinds #-} {-# LANGUAGE NoMonomorphismRestriction #-} import GHC.Exts (Constraint) type family Parent a class C a b where f :: b -> a -> String instance (C (Parent a) b) => C a b where f _ _ = f (undefined :: b) (undefined :: Parent a) data A1 = A1 data A2 = A2 data A3 = A3 data A4 = A4 type instance Parent A2 = A1 type instance Parent A3 = A2 type instance Parent A4 = A3 data F1 = F1 data F3 = F3 instance C A1 F1 where f _ _ = "F1" instance C A3 F3 where f _ _ = "F3" type family Constraints t a :: Constraint data D t = forall a. (Constraints t a) => D a type instance Constraints A1 a = (C a F1) type instance Constraints A2 a = (C a F1, C a F3) type instance Constraints A3 a = (C a F1, C a F3) type instance Constraints A4 a = (C a F1, C a F3) main = do putStrLn (f F1 A1) putStrLn (f F1 A2) putStrLn (f F1 A3) putStrLn (f F1 A4) putStrLn (f F3 A3) putStrLn (f F3 A4) putStrLn $ (\fn (D x) -> f fn x) F1 ((D A1) :: D A1) putStrLn $ (\fn (D x) -> f fn x) F1 ((D A2) :: D A1) putStrLn $ (\fn (D x) -> f fn x) F3 ((D A3) :: D A2) -- h = (\fn (D x) -> f fn x)

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Re: [Haskell-cafe] pqueue - repository and maintainer (taking over)
by Louis Wasserman 28 May '15

28 May '15

No, it's not; I never did put it up on github. On Wed, May 27, 2015 at 11:18 PM Tobias Brandt <tob.brandt(a)gmail.com> wrote: > I have an open pull request for this issue since February: > https://github.com/bumptech/haskell-pqueue/pull/2 > > But I don't even know whether this is the official repository. > > On Wed, May 27, 2015 at 10:01 PM lennart spitzner < > lsp(a)informatik.uni-kiel.de> wrote: > >> Greetings, >> >> Regarding the pqueue package: >> >> 1) Does anyone have any (additional) contact details for the current >> maintainer/author, Louis Wasserman? >> 2) Is the package's repository available anywhere? The darcs link >> listed in the package 404s. >> 3) I would be willing to take over for basic maintenance if the >> current maintainer is unavailable. >> >> The pqueue package does not compile with ghc-7.10. Fixing requires >> just some quick changes (i have a working version locally). The last >> upload for the package is from 2012, but the author's github account >> lowasser shows some more recent activity. Yet I have not received a >> reply to my e-mail from six weeks ago. >> >> Lennart >> > _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> >

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Libraries Mailing Problem?
by Dominic Steinitz 28 May '15

28 May '15

Is there something wrong with the libraries mailing list? There doesn’t seem to have been any traffic since 18 May: https://mail.haskell.org/pipermail/libraries/2015-May/date.html <https://mail.haskell.org/pipermail/libraries/2015-May/date.html> Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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International Conference on Live Coding, 13-15 July, Registration open
by alex 28 May '15

28 May '15

First International Conference on Live Coding ICSRiM, School of Music, University of Leeds 13th-15th July 2015 http://iclc.livecodenetwork.org/ We are happy to announce that registration for ICLC2015 is now open. Live coding turns programming languages into live interfaces, allowing us to directly manipulate computation via its notation. Live coding has great potential, being used for example to create improvised music and visuals, to allow developers to collaborate in new ways, to better understand computational models by making fundamental changes to them on-the-fly, and to find new ways to learn and teach programming. Since the beginning of the TOPLAP movement in 2003 (building on an extensive but hidden pre-history), live coding has grown fast, attracting interest from many people in artistic, creative, scientific, educational, business and mixed contexts. After a good number of international events, the time is right to bring these people together for an academic conference, exchanging ideas and techniques, and enjoying dozens of peer reviewed papers and performances. The conference will also open up the field for people new to live coding, so they may develop and contribute their own perspectives on this emerging field. Join us! Registration is £80 (£50 concessions) for the three day conference including lunches, evening events, and more. See the website for details of the developing programme: http://iclc.livecodenetwork.org/ And register here, completing both the on-line payment and registration forms: http://iclc.livecodenetwork.org/registration.html ICLC is organised by the Live Coding Research Network, which is funded by the Arts and Humanities Research Council. -- http://yaxu.org/

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no Web-Security component in Haskell?
by Thomas Koch 28 May '15

28 May '15

Hallo, I did not found anything comparable to Spring Security[1][2] (Java) or Symfony Security[3] (PHP) in Haskell. Both components are used in web applications to grant or deny access to resources based on roles, ACLs or custom voters. A naive strategy would be to port the concepts of both components, which are very similar, to Haskell. They represent a lot of accumulated knowledge from many experts about web security. Or are there better ways to do web security in a powerful language like Haskell? Regards, Thomas Koch [1] http://projects.spring.io/spring-security [2] http://docs.spring.io/autorepo/docs/spring-security/3.1.7.RELEASE/apidocs [3] http://api.symfony.com/master/Symfony/Component/Security/Core/SecurityConte…

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Taking over protocol-buffers package
by Kostiantyn Rybnikov 28 May '15

28 May '15

Hi Chris and Cafe! I've sent Chris an email couple days ago, this is another one to have haskell-cafe CCed in order to request maintainership of protocol-buffers package. Stefan Wehr actually tried to contact Chris long time ago, and thus you can see current "riak" package depends upon protocol-buffers-fork package, created to add support for GHC 7.8. I'd like to incorporate work from protocol-buffers-fork, add support for GHC 7.10, and also move project to GitHub and add some README with at least basic tutorial. Thanks! Awaiting few weeks now :)

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how to organize a parallel parser/compiler
by Maurizio Vitale 27 May '15

27 May '15

hello haskell-cafe, suppose you have a compiler pipeline roughly similar to (from write you a Haskell <http://dev.stephendiehl.com/fun/007_path.html> ): modl :: FilePath -> L.Text -> CompilerM () modl fname = parseP fname >=> dataP >=> groupP >=> renameP >=> desugarP >=> inferP >=> evalP and suppose you have a language where you can compile multiple files and compilation must be made _as if_ files were concatenated together in the order given on the command line (there might be side effects that affect parsing of subsequent files); still in the average case there're no dependencies and files could be compiled in parallel (or some of the dependencies can be handled at the AST level as one can prove they don't affect parsing but only aspects of the AST that can be patched). What are good strategies for dealing with this and rerun some of the parseP functions (and in the simplest solution the complete pipeline after it). The strategy I have in mind now doesn't mix well with the above pipeline, so I'd like to see if there're alternative solutions. Basically, what I have in mind is: - each parse function gets a file, something to watch on for the result of the previous parse (let's say an MVar, or some variation of speculation <https://hackage.haskell.org/package/speculation> , not sure yet) and an input environment (same for everybody). It produces an AST + what he's sensitive to (e.g. what would have affected the parsing) and what he generates that the next guy must be sensitive to. - before producing the 'what it generates part', it must be sure to have completed a valid parse, so he'll wait on the input MVar to know that the previous files have been parsed properly and that whatever side effects it caised wouldn't affect parsing. This wait will be done on a thread that doesn't count towards the parallelism limit as it is presumably cheap and we don't really serialize the parsing. [a similar question related to the above pipeline would be how do I fit in any kind of global transformation pass] Is there any library or other ideas on how to combine multiple pipelines where we want to run them with maximum parallelism but the outcome of (even a partial step of) one pipeline can invalidate and require to rerun others? Thanks for any idea, Maurizio

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ZeroMQ Thread Safety
by David Turner 27 May '15

27 May '15

Hi all, According to the ZeroMQ docs[1]: "Individual ØMQ sockets are not thread safe except in the case where full memory barriers are issued when migrating a socket from one thread to another." The Haskell ZeroMQ binding [2] is a fairly thin wrapper around the C API, and in particular doesn't seem to do much to enforce thread safety as described above. My question: do I need to use bound threads to call functions on sockets to ensure that all the foreign calls happen on the same OS thread, or is it the case that two consecutive foreign calls in a single Haskell thread have a "full memory barrier" between them if they end up being called from different OS threads? Thanks in advance, David [1] http://api.zeromq.org/4-0:zmq [2] http://hackage.haskell.org/package/zeromq4-haskell

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Account for the Haskell Wiki
by Alois Cochard 27 May '15

27 May '15

Hi, I would like a user account to access the Haskell wiki. Desired username: 'aloiscochard' Cheers -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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ClassyPrelude vs. Haskell.Language.Interpreter
by Mike Meyer 26 May '15

26 May '15

No answer on -beginners, so I'm trying -cafe. I'm trying to run interpreted code via ClassyPrelude, and getting some results that make me suspect a bug in the Prelude's type system. Or maybe the interpreter. Anyway, here's a bit of code that works as expected: {-# LANGUAGE NoImplicitPrelude #-} import ClassyPrelude import Language.Haskell.Interpreter main :: IO () main = do fun <- runInterpreter $ makeFun "reverse" case fun of Left e -> print e Right f -> readFile "/etc/motd" >>= hPut stdout . f makeFun expr = do set [languageExtensions := [NoImplicitPrelude]] setImportsQ [("ClassyPrelude", Nothing)] interpret expr (as :: Text -> Text) I don't think I can simplify this any further. It works as expected, and also works as expected, and prints out the contents of /etc/motd reversed. However, if you change the type signature in the last line from Text -> Text to LText -> Ltext (to get lazy text), you get no output. But if you change the function in the first line after main from "reverse" to "id", it works. So far, it might be an issue with lazy IO. However, change the type signature in the last line to LText -> Text. In this case, there is no output for either value of the expression. I expect an error in this case, as neither id nor reverse should be able to have the type LText -> Text! So, is there something I missed in either ClassyPrelude or the Interpreter? Or is this a subtle interaction, in which case can someone suggest a workaround? Or have I found a bug in one of the two?

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Re: [Haskell-cafe] Installing ghc-mod on Windows
by Anakreontas 26 May '15

26 May '15

I think cabal reported errors regarding the header files where in fact the problem was that it could not find a c compiler. I tried to install QuickCheck and the primitives package required by QuickCheck failed to install with errors related to header files. After installing gcc, primitives and QuickCheck installed without errors. On Tuesday, May 26, 2015 at 11:18:30 AM UTC+1, Anakreontas wrote: > > ... continued from previous message > .. even with command cabal install --extra-include-dirs=include cabal > still reports an error. > The header file is useful for older ghc versions that the one I have so > removing the dependency on the header resolved the problem. > > On Tue, May 26, 2015 at 11:16 AM, Anakreontas Mentis < > anakreonmejdi(a)gmail.com> wrote: > >> I installed the MinGHC distribution but it did not solve the problem. >> >> To install ghc-mod I had to: >> 1) cabal install ghc-mod >> to install what cabal can build without errors. >> 2) Modify the cabal file of ansiterminal according to Roman's advice. It >> installed successfully. >> 3) Modify the cabal file of lifted-base where I removed the Include-dirs >> and Includes directives and all references to inlinable.h from the source >> files. >> cabal reports that it can not find the header file or it is damaged. >> The file exists in the include directory but even with >> >> On Fri, May 22, 2015 at 7:58 PM, Michal Antkiewicz < >> mantkiew(a)gsd.uwaterloo.ca> wrote: >> >>> There used to be a big warning "don't download just the ghc. Use the >>> platform. " before. >>> >>> Nowadays, it's best to get MinGHC from >>> >>> https://www.haskell.org/downloads/windows >>> >>> this distribution is best, it'll allow you build the network package and >>> other things like the ansi-terminal, etc. >>> >>> Get the 32bit installer. >>> >>> Michał >>> >>> On Fri, May 22, 2015 at 2:10 PM, <anakreonmejdi(a)gmail.com> wrote: >>> >>>> Hello. >>>> I don't know the MinGHC release. To install ghc I downloaded a windows >>>> install program from https://www.haskell.org/ghc/. >>>> >>>> >>>> Michal Antkiewicz <mantkiew(a)gsd.uwaterloo.ca> writes: >>>> >>>> > Hi, >>>> > >>>> > are you using msys and MinGHC? >>>> > >>>> > For now, I clone ghc-mod @ master and just cabal install it (with >>>> MinGHC >>>> > 0.7.10 and cabal 1.22) within msys. It has not been released yet. >>>> > >>>> > Michał >>>> > >>>> > On Fri, May 22, 2015 at 12:09 PM, Roman Cheplyaka <roma(a)ro-che.info> >>>> wrote: >>>> > >>>> >> On 22/05/15 18:06, Anakreontas wrote: >>>> >> > I tried to instal ghc-mod on Windows with cabal. Two dependencies >>>> fail >>>> >> > to compile because of missing native libraries. >>>> >> > ansi-terminal requires kernel32 and >>>> >> > lifted-base requires inlinable.h. >>>> >> > >>>> >> > Have you solved a similar problem? In Linux it would be easy to >>>> install >>>> >> > the native libraries but in Windows I do not know which programs I >>>> >> > should install and where to find them. >>>> >> >>>> >> You should be able to install ansi-terminal by patching its cabal >>>> file, >>>> >> see https://github.com/feuerbach/ansi-terminal/issues/6 >>>> >> >>>> >> Once again, I'm asking Windows users and developers for their input >>>> on >>>> >> this issue. >>>> >> >>>> >> Roman >>>> >> >>>> >> >>>> >> _______________________________________________ >>>> >> Haskell-Cafe mailing list >>>> >> Haskell-Cafe(a)haskell.org >>>> >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >>>> >> >>>> >> >>>> >>>> -- >>>> >>> >>> >> >

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aeson-utils: aeson-0.9 compatibility package
by Adam Bergmark 25 May '15

25 May '15

Hi folks, aeson-0.9 was released today. It changes the behavior of `decode` and `eitherDecode`: They now both allow atomic values on the top level. Previously the behavior was inconsistent, `encode 1 = "1"` but `decode "1" :: Maybe Int = Nothing`. aeson-utils[1] has the functions `decodeV` and `eitherDecodeV` that work like aeson-0.9's `decode` and `eitherDecode` respectively, also with older aeson versions. If you want to stay backwards compatible without having varying semantics based on dependencies, check it out! [1] http://hackage.haskell.org/package/aeson-utils Regards, Adam

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Any recommendations on how to interact with the running state of a program?
by Anatoly Yakovenko 25 May '15

25 May '15

I am playing around with some deep learning algorithms and I need a way to periodically read the intermediate result and change some of the system variables. Any ideas on how to best approach this problem? I was thinking of something basic, like having the program periodically read and write from some files. Thanks, Anatoly

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New Functional Programming Job Opportunities
by Functional Jobs 25 May '15

25 May '15

Here are some functional programming job opportunities that were posted recently: Clojure/Erlang backend engineer/architect at Zoomo http://functionaljobs.com/jobs/8831-clojure-erlang-backend-engineer-archite… Cheers, Sean Murphy FunctionalJobs.com

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ANN: Leksah 0.15
by Hamish Mackenzie 25 May '15

25 May '15

Hi Everyone, The new leksah package is in Hackage and the installers for Windows and OS X are available for download at: https://github.com/leksah/leksah/wiki/download (remember to choose the one that matches your GHC version) Nw in this release: * Support for GHC 7.10.1. * Uses Gtk+ 3.16 on Windows and OS X. * GtkInspector works on all platforms (Ctrl+Shift+I). * Updated build instructions https://github.com/leksah/leksah (OS X and Windows builds are fairly easy now). * Underlining of doctest failures. * Lots of bug fixes. Things that are new since 0.14.0: * Support for using GHCJS. https://www.youtube.com/watch?v=zQnExdDL63c * GtkInspector https://wiki.gnome.org/Projects/GTK%2B/Inspector. * Web Inspector pane (right click on output pane to bring it up. https://trac.webkit.org/wiki/WebInspector * Cabal commands executed by Leksah show up in the log pane. I remain optimistic about the future of Leksah. GTK+ has improved hugely in the last couple of years. Also WebKitGTK+ and GHCJS mean integrating tools into Leksah will be easier than ever. A great many people contribute (mostly indirectly) to Leksah, it is much appreciated and I hope that number will grow. As always, please help! Hop on #leksah or file and issue at https://github.com/leksah/leksah/issues, even if it is just to vent your displeasure with Leksah (every bug report helps). Here are some fun ideas you might like to try working on if you are looking for a way to contribute to Leksah: * Try using Leksah and fix the thing that annoys you most about it. * Figure out if/how ide-backend can be used in Leksah. * Create an XMonad like manager for <div> based panes. Ideally it would work for both GTK+ and GHCJS. * Migrate existing UI components from Gtk+ to GHCJS. * Anything GHCJS based and then add support in Leksah for it. * GHCJS based scripting (make it work for Leksah like elisp for Emacs). * Improve Yi integration. What we have is unusably incomplete. * Add GHCJS backend for Yi (replacing the Pango one). * Improve JavaScript based editor support (currently only CodeMirror is supported and not very well). * Add support for using SoH and/or FPView within Leksah. If you are interested in any of these please let me know and I will do what I can to help you get started. Hamish PS. I am kind of sad Eclipse FP has stalled for now and I hope it restarts soon. Integrating Haskell into existing IDEs (especially those with large user bases) will help sell Haskell to the world. I wish JP well and I am sure he will find something interesting and challenging to work on next.

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Increasing parallelism in a frequency counter
by Andreas Pauley 25 May '15

25 May '15

Hi everyone, I've started playing with some parallel programming in Haskell, mostly by applying the first few examples from Simon Marlow's book to my own toy problem: https://github.com/apauley/parallel-frequency I'm quite pleased with the speedup I have so far, the fastest parallel implementation is just over twice as fast as its sequential counterpart. But looking at the threadscope images from the generated event logs I can see that there are still significant portions of my program that runs on only one core. Is anyone interested to see if we can increase the parallelism in this frequency counter? Kind regards, Andreas -- https://keybase.io/apauley http://za.linkedin.com/in/apauley http://www.meetup.com/lambda-luminaries http://www.meetup.com/Bitcoins-Baby-Bitcoins GPG Public Key: https://keybase.io/apauley/key.asc

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Fwd: Abandoning String = [Char]?
by David Feuer 25 May '15

25 May '15

Performance will go utterly out the window if you use pattern synonyms and the like to pretend that Text is [Char]. It would probably work fine (great, even) when matching, but code that assumes String=[Char] would be completely killed on the construction side, because building Text by consing, or repeatedly prepending small chunks, is ridiculously inefficient. These are the very things that are *efficient* with [Char], and that people have assumed to be efficient when writing code that uses it. On May 22, 2015 5:58 PM, "Carter Schonwald" <carter.schonwald(a)gmail.com> wrote: > > one direction that this thread has *COMPLETELY* overlooked is the following: > > could we use pattern synonyms or something along those lines to make the migration to Text or the like more seemless?

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Munich Haskell Meeting, 2015-05-25 @ 19:30
by Christian Neukirchen 23 May '15

23 May '15

Dear all, Next week, our monthly Munich Haskell Meeting will take place again on Monday, May 25 at Cafe Puck at 19h30. For details see here: http://www.haskell-munich.de/dates 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-may-2015/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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open gl type conversions
by briand＠aracnet.com 23 May '15

23 May '15

Following code GLFW.setWindowSizeCallback w (Just (\window w h -> do GL.viewport $= (GL.Position 0 0, GL.Size w h) emo1.hs:42:50: Couldn't match type ‘Int’ with ‘Foreign.C.Types.CInt’ Expected type: GLsizei Actual type: Int In the first argument of ‘Size’, namely ‘w’ In the expression: Size w h I can never seem to figure out if i really need to do a type conversion, or just the make the appropriate type declarations. Sometimes it seems to be a combination of both. Part of the complication here is that w and h are, in fact, `Int` because that's there type in the type signature of WindowSizeCallback (Window -> Int -> Int -> IO () ). GL.Size really needs a CInt so it seems like I have to do some sort of explicit conversion, but I can never seem to figure out exactly how to find the necessary function. Humorously i tried putting Int->CInt in hoogle, and the only thing that looked like it might be useful was unsafeCoerce, but I'm pretty sure that's not the right answer. I was wondering if someone could enlighten me on exactly how you can trace out the solution to this sort of problem because it seeems to come up often (see, for example my confusion over FFTW r). Brian

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Abandoning String = [Char]?
by Andrew Gibiansky 22 May '15

22 May '15

Hey all, In the earlier haskell-cafe discussion of IsString, someone mentioned that it would be nice to abandon [Char] as the blessed string type in Haskell. I've thought about this on and off for a while now, and think that the fact that [Char] is the default string type is a really big issue (for example, it gives beginners the idea that Haskell is incredibly slow, because everything that involves string processing is using linked lists). I am not proposing anything, but am curious as to what already has been discussed: 1. Has the possibility of migrating away from [Char] been investigated before? 2. What gains could we see in ease of use, performance, etc, if [Char] was deprecated? 3. What could replace [Char], while retaining the same ease of use for writing string manipulation functions (pattern matching, etc)? 4. Is there any sort of migration path that would make this change feasible in mainline Haskell in the medium term (2-5 years)? Thanks! I would welcome any references or links that my cursory googling has failed to find. -- Andrew

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Installing ghc-mod on Windows
by Anakreontas 22 May '15

22 May '15

I tried to instal ghc-mod on Windows with cabal. Two dependencies fail to compile because of missing native libraries. ansi-terminal requires kernel32 and lifted-base requires inlinable.h. Have you solved a similar problem? In Linux it would be easy to install the native libraries but in Windows I do not know which programs I should install and where to find them.

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cabal problem with Digits
by Roelof Wobben 22 May '15

22 May '15

Hello, When I want to install digits I see this output: cabal install digits Resolving dependencies.. [1 of 1] Compiling Main ( /tmp/digits-0.2-415/digits-0.2/Setup.lhs, /tmp/digits-0.2-415/digits-0.2/dist/setup/Main.o ) /tmp/digits-0.2-415/digits-0.2/Setup.lhs:3:3: Warning: Module ‘System.Cmd’ is deprecated: Use "System.Process" instead /tmp/digits-0.2-415/digits-0.2/Setup.lhs:5:49: Warning: In the use of ‘runTests’ (imported from Distribution.Simple, but defined in Distribution.Simple.UserHooks): Deprecated: "Please use the new testing interface instead!" Linking /tmp/digits-0.2-415/digits-0.2/dist/setup/setup ... Warning: digits.cabal: A package using 'cabal-version: >=1.2' must use section syntax. See the Cabal user guide for details. Configuring digits-0.2... Building digits-0.2... Preprocessing library digits-0.2... [1 of 1] Compiling Data.Digits ( src/Data/Digits.hs, dist/build/Data/Digits.o ) ****/usr/bin/ld: cannot find -lHSQuickCheck-2.8.1-ghc7.8.3 /usr/bin/ld: cannot find -lHStf-random-0.5-ghc7.8.3 /usr/bin/ld: cannot find -lHSprimitive-0.6-ghc7.8.3 /usr/bin/ld: cannot find -lHSrandom-1.1-ghc7.8.3**** How to soilve this one ? Roelof --- Dit e-mailbericht is gecontroleerd op virussen met Avast antivirussoftware. http://www.avast.com

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Haskell Weekly News: Issue 322
by Semen Trygubenko / Семен Тригубен ко 21 May '15

21 May '15

New Releases 99 Haskell: A web service by Bram Hoskin Solve live Haskell coding problems based on H-99 in the browser to strengthen your understanding of the language. http://www.99haskell.org/ https://github.com/bramgg/99haskell/ Magic Cookies A commercial Android game is released that is written in Haskell using SDL2 for multimedia and the Arrowized Functional Reactive Programming DSL Yampa. The authors had to "escape their functional comfort zones and come up with smarter abstractions that mutable reality and performance demand". The game consists of 2K lines of code, of which 1K is game specific and 400 are Yampa code. The most complex parts were certain Yampa constructs (arrow-based, with lots of tupling/untupling). http://keera.co.uk/blog/2015/03/19/magic-cookies-released-google-play/ https://play.google.com/store/apps/details?id=uk.co.keera.games.magiccookies https://github.com/keera-studios/keera-hails https://github.com/ivanperez-keera/Yampa Discussion Finding a GHC bug by Neil Mitchell A write up of the hunt for bug #10176 http://neilmitchell.blogspot.it/2015/03/finding-ghc-bug.html https://ghc.haskell.org/trac/ghc/ticket/10176 What are your most persuasive examples of using Quickcheck? Quickcheck helped many people in a number of areas — compiler optimisations, date/time validation, regular expressions, encoding/decoding, topological sort, fuzzing HTTP APIs and even exhibiting classical voting paradox! Apart from the obvious benefit of helping to find big juicy bugs as well as valid but potentially harmless tiny bugs in edge cases that no-one cares about, Quickcheck can help attain enlightenment in the sense that spelling out Quickcheck properties in itself can be rewarding because this can reveal assumptions that have been made without realizing it. Roman Cheplyaka reminds us about SmallCheck and that it should be used instead of Quickcheck when one has a good idea about what depth is needed and when exhaustive search at that depth is affordable. https://www.reddit.com/r/haskell/comments/308ps6/what_are_your_most_persuas… http://stackoverflow.com/questions/20092191/how-much-should-one-control-the… What is the difference between free monads and free monoids? A comment by Edward Kmett. https://www.reddit.com/r/haskell/comments/2znhjk/what_is_the_difference_bet… Type-Checked Pseudo-Code Tom Ashworth argues that Haskell is an excellent tool for fleshing out ideas and prototyping solutions, and that it makes one generalize and shake out many conceptual bugs before concepts become code. https://phuu.net/2015/03/24/type-checked-pseudo-code.html Where does GHC spend most of it's time during compilation? Optimisation and codegen, it seems. Also, GHC compilation times went up substantially from version 7.6 to 7.8. https://www.reddit.com/r/haskell/comments/309430/where_does_ghc_spend_most_… Quotes of the Week "Haskell doesn't feel like code. It feels like a language for thinking in: it's expressive, terse and simple, especially as type-checked pseudo-code." (Tom Ashworth) https://phuu.net/2015/03/24/type-checked-pseudo-code.html "Well that's not in the spec. If you want to change the requirements you have to renegotiate the contract =P" (sccrstud92) https://www.reddit.com/r/haskell/comments/2zxekg/while_learning_haskell_i_m… "Unit tests are double entry bookkeeping" (EvanDaniel) https://www.reddit.com/r/haskell/comments/308ps6/what_are_your_most_persuas… augustss> "Well, type checking is worst case exponential…" barsoap> "Yep. That's also the reason why I don't really get the insistence of dependently-typed languages to have to be total at the type level: I don't care whether type-checking takes ten or infinitely many years, both figures are too large." https://www.reddit.com/r/haskell/comments/309430/where_does_ghc_spend_most_… "Our prophet Djistra said that a testing shows the presence, not the absence of bugs … <snip> … Today Djistra would have been stoned under a myriad of inutile unit tests that people perform for a sense of false security, in a sort of superstitious sacrificial ritual, a waste of time to convince himself and others that his software is right." (agocorona) https://www.reddit.com/r/haskell/comments/308ps6/what_are_your_most_persuas… "You might also consider these sorts of infelicities as teachable moments" (ericpashman) https://www.reddit.com/r/haskell/comments/2zxekg/while_learning_haskell_i_m… "Nice gradual progression there. Big O notion, smoothly divided into 3 easy parts, then bam, Coyoneda. =) I approve. [Yes, I realize it is a bag of topics, not a course outline, but it still grabbed me.]" (edwardkmett) https://www.reddit.com/r/haskell/comments/2zqyes/we_released_a_video_librar…

1 4

23% of calls to map fuse away
by Joachim Breitner 21 May '15

21 May '15

Hi, I just compiled all¹ of Stackage LTS 2.9 with GHC 7.8.4 with -ddump-rule-firings, and counted the occurrences of the rules. Here is a fun fact: 23% of all (static) occurrences of "map" fuse away². And 50387 lists are fused away in total³ Full data at https://gist.github.com/nomeata/071c1f87450cf668bbeb Greetings, Joachim ¹ but the SDL2 bindings ² 16925 × rule map 12904 × rule mapList, which fires if no fusion happened. ³ 27846 × rule fold/build 11293 × rule foldr/single 11248 × rule augment/build -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

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I'm reading #OutOfTheTarPit does ghc have a relational model built in for state?
by KC 21 May '15

21 May '15

I'm reading #OutOfTheTarPit does ghc have a relational model built in for state? "Out of the Tar Pit" talks about FRP - Functional Relational Programming -- -- Sent from an expensive device which will be obsolete in a few months! :D Casey

5 5

Library design around FFI library
by Marco Zocca 21 May '15

21 May '15

I'm implementing the low-level interface to a large C library (using c2hs). The C functions can be broadly classified by: *) the main datastructure they operate on, e.g. returnType AFunction (A* a, ...); *) creation, modification, read access, destruction operations for each of these datastructures, following a common pattern: ACreate(), ASet1(), ASet2(), .., ARead(), ADestroy(), BCreate(), etc. The library rests on top of MPI, so there are e.g. AScatterBegin(), AScatterEnd() function pairs that account for potentially large delays associated with computing and moving data around. On the Haskell side, the C pointer types are represented as e.g. data Ah = Ah (Ptr Ah) deriving instance Storable Ah and e.g. a Create function returns the representation of the fresh pointer along with the usual integer error code: ahCreate :: MPIComm -> IO (Ah, Err) What abstraction may I use to capture logic such as: *) separate read-only functions from the potentially overwriting ones *) guarantee precedence relations (e.g. computation can only occur after initialization) *) collect or even compose error codes, letting computation go through iff Err==0 (e.g. a n-ary Maybe ?) Sequencing in the IO monad causes all effectful functions to run and return their result and/or error code. All feedback is welcome; Thank you in advance

1 1

NoOO languages
by Harry . 20 May '15

20 May '15

Could we mimic the marketing success of NoSQL databases by branding functional languages as NoOO (or even NoIO)?

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[ANN] codex 0.3
by Alois Cochard 20 May '15

20 May '15

Hello Café, I have released a new version of `codex`[1] (a ctags file generator for cabal project and their dependencies). It should be noted that *this version now fully support the windows operating system*, thanks to a great contribution from Ben James. This new version include: - Tagging of the current project can be turned-off - Fix/Enhance the `emacs` and `sublime` default format - Tags file name is now configurable - Replace `curl` with `wrep` - Misc fixes and portability enhancement Thanks to the contributors (Ben James, Tal Walter, Eyal Lotem). [1] https://github.com/aloiscochard/codex -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

1 0

glfw demos ?
by briand＠aracnet.com 20 May '15

20 May '15

Hi, Looks like the demos, including the one on the wiki page, and the glfw-b-demo package, are suffering from bit-rot. I was hoping somebody could point me to a small get-started demo. Meanwhile I am working on trying to get the wiki demo running. Thanks, Brian

2 1

text-icu (and FFI in general) on Windows 64 bits
by Yitzchak Gale 20 May '15

20 May '15

I was finally successful in getting text-icu to work on Windows 64 bits. This is probably an indication of what to expect in general for packages requiring FFI on Windows 64 bits. In the past, on 32 bits, the standard Windows binary distribution from the ICU site could be used together with msys/mingw, even though it was officially only for MSVC. This no longer seems to be the case for 64 bits. When I build text-icu in that way with a 64 bit GHC and the Windows 64-bit binary ICU distribution for MSVC, the resulting EXEs segfault as soon as any function from text-icu is called. There is no official ICU download for mingw-w64 binaries. But happily, the MSYS2 project does provide a pre-built ICU binary distribution for mingw-w64. It tends to be quite up-to-date; the current version is ICU 55.1. Note, however, that I was *not* able to use the partial MSYS2 that comes with MinGHC, because pacman seems to be missing. So the solution is: 1. Download and install 64-bit MSYS2, following the instructions on the site: http://msys2.github.io 2. In the MSYS2 shell window, get the ICU package for mingw-w64: pacman -S mingw64/mingw-w64-x86_64-icu 3. Now you can build the Haskell text-icu library using this command: cabal install --extra-lib-dirs="c:\path\to\msys64\mingw64\lib" --extra-include-dirs="c:\path\to\msys64\mingw64\include" text-icu 4. Provide the following DLLs with your EXE that uses text-icu: libicudt55.dll libicuin55.dll libicuuc55.dll libgcc_s_seh-1.dll libstdc++-6.dll Get them from: c:\path\to\msys64\mingw64\bin This not only compiles, but EXEs produced using this library actually run without segfaulting. You can even compile native Windows EXEs from C using ICU this way, with the gcc that is put on your path by the Haskell Platform installer (and probably also MinGHC, but I didn't try that). Just include -L and -I options to gcc with the same paths as above, and make sure to specify -licuuc -licudt etc. as needed. -Yitz

1 1

Automated Differentiation of Matrices (again)
by Florian Hofmann 20 May '15

20 May '15

In [1](this) email thread Edward Kmett and Dominic Steinitz discuss the state of interoperability of `ad` and `hmatric` (or `repa`) with Edward hinting that the 4.0 line of `ad` might improve on the situation. Could someone elaborate on the state of affairs two years later? Florian [1]: https://mail.haskell.org/pipermail/haskell-cafe/2013-April/107561.html

2 2

Naming convention for version branches (Package versioning)
by Alois Cochard 20 May '15

20 May '15

Hi all, I am currently writing a tool to automate the release and version bump of cabal projects. Currently you can call the tool by giving as argument the rank of the branch you want to bump, for example given 0.0.0.0: - `cabal-release 0` bump to `1` - `cabal-release 1` bump to `0.1` - `cabal-release 2` bump to `0.0.1` - `cabal-release 3` bump to `0.0.0.1` As we are not all robots (yet), I thought that in addition to this it would be great if the user could give a human friendly name for the rank. For now, here is what I have for the different rank: 0 == --major 1 == --major-fix 2 == --minor 3 == --minor-fix I'm curious to know what you think of those names? any suggestions or known established convention about that? Thanks -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

4 6

advanced cabal configuration
by Kazu Yamamoto 20 May '15

20 May '15

Hi, I'm a maintainer of simple-sendfile and need to implement the following is to rescue 32bit Linux: - If the COff size is 8, the following FFI is used: foreign import ccall unsafe "sendfile64" c_sendfile :: Fd -> Fd -> Ptr COff -> CSize -> IO (#type ssize_t) - Otherwise, the following FFI is used: foreign import ccall unsafe "sendfile" c_sendfile :: Fd -> Fd -> Ptr COff -> CSize -> IO (#type ssize_t) How can I implement this? I guess that Setup.hs should evaluate (sizeOf (1 :: COff)) and define a C macro, say LARGE_OFFSET and write the following code. #ifdef LARGE_OFFSET foreign import ccall unsafe "sendfile64" #else foreign import ccall unsafe "sendfile" #endif I have no experience to use Build-Type: other than Simple in cabal files. Would someone explain how to implement it concretely or suggest examples which implement similar things? For more informaion, please read: https://github.com/yesodweb/wai/issues/372 Thanks. --Kazu

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Re: [Haskell-cafe] Request for maintainers
by Fred Ross 19 May '15

19 May '15

Thank you! I've added you to the maintainers list. You might want to go ahead and fork the repository at https://github.com/madhadron/serial, update serial.cabal with your info, and upload a new version. Fred Ross On May 18, 2015, at 11:05 AM, Jose Calderon <jmct(a)cs.york.ac.uk> wrote: > Hello, > > I'll happily take the serial library off your hands. > > My hackage username is jmct. > > Cheers, > > Jose > http://jmct.cc > > > > On 18 May 2015 at 02:34, Fred Ross <madhadron(a)gmail.com> wrote: > I have finally accepted that I won't be part of the Haskell community in any real sense in the foreseeable future. There are three libraries that I am still the maintainer of that I need to hand off. Is there anyone who would take over any of the following? > > hdaemonize - Utilities for writing Unix daemons in Haskell > serial - Serial port access library > hscamwire - FFI bindings to camwire to access IIDC1394 Firewire cameras > > Fred Ross > http://madhadron.com >

1 0

Request for maintainers
by Fred Ross 19 May '15

19 May '15

I have finally accepted that I won't be part of the Haskell community in any real sense in the foreseeable future. There are three libraries that I am still the maintainer of that I need to hand off. Is there anyone who would take over any of the following? hdaemonize - Utilities for writing Unix daemons in Haskell serial - Serial port access library hscamwire - FFI bindings to camwire to access IIDC1394 Firewire cameras Fred Ross http://madhadron.com

2 1

Automatically generate sum type members -> [String]
by Cody Goodman 19 May '15

19 May '15

Can I use either template Haskell, GHC Generics, or something else to get the list of Constructors in Codes? Then I could do `map show codeSumTypeMembers` and get `["A0100A","A0500A"]`? Here's an example of solving this problem manually: data Codes = A0100A | A0500A deriving Show codeExists "A0100A" = True codeExists "A0500A" = True codeExists _ = False main = print $ codeExists xmlElementName where xmlElementName = "A0500A" -- λ> main -- True

8 8

New Functional Programming Job Opportunities
by Functional Jobs 18 May '15

18 May '15

Here are some functional programming job opportunities that were posted recently: Senior Software Engineer (Functional Programming/Scala) at AdAgility http://functionaljobs.com/jobs/8826-senior-software-engineer-functional-pro… Cheers, Sean Murphy FunctionalJobs.com

1 0

data EitherF m1 m2 a = LeftF (m1 a) | RightF (m2 a)
by Daniel van den Eijkel 18 May '15

18 May '15

Hi, I am wondering if there is a library with a datatype like the following defined: data EitherF m1 m2 a = LeftF (m1 a) | RightF (m2 a) I could not find anything with Hoogle. Does anybody know such a thing? Thank you & best, Daniel

3 3

FIXME pragma
by Christopher Done 18 May '15

18 May '15

What's the feeling on having a FIXME pragma so that I can attach warnings to unfinished things? {-# FIXME foo "Reasons here." #-} I would use the WARNING pragma but that doesn't work within a module and only triggers on use. Compiler errors are the one thing I and everyone else pays attention to, it would be very handy to have more control over things GHC reports to the developer to aid development. Ciao

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OCL 2015: First Call for Papers
by Achim D. Brucker 18 May '15

18 May '15

(Apologies for duplicates) CALL FOR PAPERS 15th International Workshop on OCL and Textual Modeling Tools and Textual Model Transformations Co-located with ACM/IEEE 18th International Conference on Model Driven Engineering Languages and Systems (MODELS 2015) September 28th, 2015, Ottawa, Canada http://ocl2015.lri.fr Modeling started out with UML and its precursors as a graphical notation. Such visual representations enable direct intuitive capturing of reality, but some of their features are difficult to formalize and lack the level of precision required to create complete and unambiguous specifications. Limitations of the graphical notations encouraged the development of text-based modeling languages that either integrate with or replace graphical notations for modeling. Typical examples of such languages are OCL, textual MOF, Epsilon, and Alloy. Textual modeling languages have their roots in formal language paradigms like logic, programming and databases. The goal of this workshop is to create a forum where researchers and practitioners interested in building models using OCL or other kinds of textual languages can directly interact, report advances, share results, identify tools for language development, and discuss appropriate standards. In particular, the workshop will encourage discussions for achieving synergy from different modeling language concepts and modeling language use. The close interaction will enable researchers and practitioners to identify common interests and options for potential cooperation. Topics of interest include (but are not limited to) =================================================== - Mappings between textual modeling languages and other languages/formalisms - Algorithms, evaluation strategies and optimizations in the context of textual modeling languages for -- validation, verification, and testing, -- model transformation and code generation, -- meta-modeling and DSLs, and -- query and constraint specifications - Alternative graphical/textual notations for textual modeling languages - Evolution, transformation and simplification of textual modeling expressions - Libraries, templates and patterns for textual modeling languages - Tools that support textual modeling languages (e.g., verification of OCL formulae, runtime monitoring of invariants) - Complexity results for textual modeling languages - Quality models and benchmarks for comparing and evaluating textual modeling tools and algorithms - Successful applications of textual modeling languages - Case studies on industrial applications of textual modeling languages - Experience reports -- usage of textual modeling languages and tools in complex domains, -- usability of textual modeling languages and tools for end-users - Empirical studies about the benefits and drawbacks of textual modeling languages - Innovative textual modeling tools - Comparison, evaluation and integration of modeling languages - Correlation between modeling languages and modeling tasks This year, we particularly encourage submissions describing tools that support - in a very broad sense - textual modeling languages (if you have implemented OCL.js to run OCL in a web browser, this is the right workshop to present your work) as well as textual model transformations. Venue ===== The workshop will be organized as a part of MODELS 2015 Conference in Ottawa, Canada. It continues the series of OCL workshops held at UML/MODELS conferences: York (2000), Toronto (2001), San Francisco (2003), Lisbon (2004), Montego Bay (2005), Genova (2006), Nashville (2007), Toulouse (2008), Denver (2009), Oslo (2010), Zurich (2011, at the TOOLs conference), 2012 in Innsbruck, 2013 in Miami, and 2014 in Valencia, Spain. Similar to its predecessors, the workshop addresses both people from academia and industry. The aim is to provide a forum for addressing integration of OCL and other textual modeling languages, as well as tools for textual modeling, and for disseminating good practice and discussing the new requirements for textual modeling. Workshop Format =============== The workshop will include short (about 15 min) presentations, parallel sessions of working groups, and sum-up discussions. Submissions =========== Three types of papers will be considered: * short papers (between 6 and 8 pages) describing ideas, * tool papers (between 6 and 8 pages), and * full papers (between 12 and 16 pages) in LNCS format. Submissions should be uploaded to EasyChair (https://easychair.org/conferences/?conf=ocl20150) The program committee will review the submissions (minimum 2 reviews per paper, usually 3 reviews) and select papers according to their relevance and interest for discussions that will take place at the workshop. Accepted papers will be published online in a pre-conference edition of CEUR (http://www.ceur-ws.org) Important Dates =============== Submission of papers: July 17, 2015 Notification: August 21, 2015 Workshop date: September 28, 2015 Organizers ========== Achim D. Brucker, SAP SE, Germany Marina Egea, Indra Sistemas S.A., Spain Martin Gogolla, University of Bremen, Germany Frederic Tuong, Univ. Paris-Sud - IRT SystemX - LRI, France Programme Committee =================== Mira Balaban, Ben-Gurion University of the Negev, Israel Tricia Balfe, Nomos Software, Ireland Achim D. Brucker, SAP SE, Germany Fabian Buettner, Inria - Ecole des Mines de Nantes, France Jordi Cabot, Inria - Ecole des Mines de Nantes, France Dan Chiorean, Babes-Bolyai University, Romania Robert Clariso, Universitat Oberta de Catalunya, Spain Tony Clark, Middlesex University, UK Manuel Clavel, IMDEA Software Institute, Spain Carolina Dania, IMDEA Software Institute, Spain Birgit Demuth, Technische Universitat Dresden, Germany Marina Egea, Indra Sistemas S.A., Spain Geri Georg, Colorado State University, USA Martin Gogolla, University of Bremen, Germany Shahar Maoz, Tel Aviv University, Israel Istvan Rath, Budapest University of Technology and Economics, Hungary Bernhard Rumpe, RWTH Aachen, Germany Frederic Tuong, Univ. Paris-Sud - IRT SystemX - LRI, France Claas Wilke, Technische Universitat Dresden, Germany Edward Willink, Willink Transformations Ltd., UK Burkhart Wolff, Univ. Paris-Sud - LRI, France Steffen Zschaler, King's College, UK -- Dr. Achim D. Brucker, SAP SE, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, http://www.brucker.ch/

1 0

CFP: Haskell Symposium Regular Track Final Call
by Ben Lippmeier 18 May '15

18 May '15

===================================================================== ACM SIGPLAN CALL FOR SUBMISSIONS Haskell Symposium 2015 Vancouver, Canada, 3-4 September 2015, directly after ICFP http://www.haskell.org/haskell-symposium/2015 ===================================================================== Reminder that the Haskell Symposium Regular Track abstract deadline is this: Tuesday 19th of May, with full papers due this: Friday 22nd of May. Authors that have *already submitted to the early track*, have until 5th of June to resubmit an improved version of those papers. Deadlines stated are valid anywhere on earth. (the HotCRP submission site states them in US EDT, but don't fret) See the website for further details http://www.haskell.org/haskell-symposium/2015 =====================================================================

1 0

Announcement: Gipeda, the git performance dashboard
by Joachim Breitner 17 May '15

17 May '15

Dear Haskellers, a while ago, I set up a performance dashboard¹ for GHC, based on codespeed², but I was dissatisfied, so in the end, I wrote a new one, called Gipeda for “Git Performance Dashboard”. The git in the name as, in contrast to codespeed, I do not try to be VCS-agnostic but do want to use and expose the structure of your project’s git repository in the output. You can have a look at http://perf.haskell.org/ghc. It should be relatively self-explanatory. Just note that by default it hides boring stuff (commits and results with no significant change), you can select what to show in the top-right corner. The idea behind gipeda is relatively simple. Starting with a directory with one file for each of your project’s benchmarked commit, gipeda digests this to produce a bunch of JSON files. It uses shake³ to avoid unnecessary recalculations. A static HTML file with lots of JavaScript (using handlebars as a templating engine, and other JS libraries like jQuery and flot) then presents this data, in a hopefully snappy and intuitive way. I have announced the GHC instance on the ghc-dev mailing list⁴, so why do I write here as well? Because you can use gipeda for your own projects! And because you can contribute! The program is not GHC-specific, so if you have a way to produce benchmark numbers (or any other kind of metric) for your project, you can feed them to gipeda to be visualized. See the README at https://github.com/nomeata/gipeda for instructions (and ask me if you are stuck). If it makes sense we can host the result at http://perf.haskell.org/ (but you still need to run the benchmarks yourself). And although it is quite nice so far, there are a lot of things it should also be able to do. Here are a few ideas: * Integrate data from multiple build hosts. * Compare the results from arbitrary two commits. * Visualize non-linear git histories, e.g. due to branches. * Know about named branches and tags. * RSS feeds and email notifications. * Find a way to efficiently run gipeda on travis. * General UI polishing. Some of that is possible without touching any JavaScript, some without touching any Haskell, so if you want to contribute, I’m sure you’ll find something. I plan to work on that during ZuriHac⁵ (only two more weeks), so if you are there and looking for a project, please join me! Greetings, Joachim ¹ http://ghcspeed-nomeata.rhcloud.com/ ² https://github.com/tobami/codespeed ³ http://shakebuild.com/ ⁴ https://mail.haskell.org/pipermail/ghc-devs/2015-May/009032.html ⁵ https://wiki.haskell.org/ZuriHac2015 PS: Thanks to davean from the haskell.org admin team for setting up perf.haskell.org. -- Joachim “nomeata” Breitner mail(a)joachim-breitner.de • http://www.joachim-breitner.de/ Jabber: nomeata(a)joachim-breitner.de • GPG-Key: 0xF0FBF51F Debian Developer: nomeata(a)debian.org

1 0

Re: [Haskell-cafe] Static executables in minimal Docker containers
by Greg Weber 17 May '15

17 May '15

Haskell is not that great at producing statically linked libraries independent of the OS. The issue you are running into would likely show up in another non-ubuntu image (or even possibly a different version of an ubuntu image), so you could probably use a Fedora image that has tracing. How are you addressing the linker warning about needing a particular glibc version at runtime? On Mon, Apr 13, 2015 at 3:28 AM, Sharif Olorin <sharif.olorin(a)gmail.com> wrote: > Unfortunately, strace and ltrace aren't available in that Docker image, >> but it's a good idea to see if I can get them running there somehow. >> > > Failing that, you might be able to get useful information of the same kind > by running docker (the server, not the `docker run` command) under perf[0] > and then running your busybox container. It should at least give you an > idea of what it's doing when it explodes. > > Sharif > > [0]: https://perf.wiki.kernel.org/index.php/Tutorial > > -- > You received this message because you are subscribed to the Google Groups > "Commercial Haskell" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to commercialhaskell+unsubscribe(a)googlegroups.com. > To post to this group, send email to commercialhaskell(a)googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/commercialhaskell/86ca2603-37f2-4645-9cd2… > <https://groups.google.com/d/msgid/commercialhaskell/86ca2603-37f2-4645-9cd2…> > . > > For more options, visit https://groups.google.com/d/optout. >

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Re: [Haskell-cafe] Haskell-Cafe Digest, Vol 141, Issue 25
by Michael Baikov 17 May '15

17 May '15

> > Suppose the following data type for encoding Boolean expressions: > > data BExpr a = BTrue > | BFalse > | Id String > | Not a > | And a a > | Or a a > | BEq a a > deriving (Functor) > type Expr = Fix BExpr > > It is easy to produce a string representation of an expression or evaluate > it: > > estr :: BExpr String -> String > eval :: BExpr Bool -> Bool > > with the cata function from Data.Functor.Fixedpoint. > > Could you suggest a solution for transforming trees encoded as Exp into > equivalent Expr (e.g Not Not a ~> a)? > cata does not work since it expects a function f a -> a while a > transformation would be f a -> f a. Actually cata works just fine, all you need following transformation which is f a -> a alg :: BExpr Expr -> Expr alg (Not (Fix (Not a))) = a alg x = Fix x

1 0

[ANN] relational-record - relational-algebraic query building DSL
by Kei Hibino 16 May '15

16 May '15

Hello everybody, I am happy to announce relational-record library and its project page. relational-record is domain specific language for type-safe SQL query building, and database access API with compile time schema generators. Code is avaiable on github and hackage. https://github.com/khibino/haskell-relational-record/ http://hackage.haskell.org/package/relational-record/ Tutorial, examples and documentations are available from project page links. http://khibino.github.io/haskell-relational-record/ Supported features are below, * Type safe query building. * Composable query. * Outer join. * Aggregation. * Compile time compile code generation along with RDBMS schema. * Schema support of ProsgreSQL, SQLite3, MySQL, IBM DB2, MicroSoft SQL Server, and Oracle. Any comments, any questions about this library are welcome. -- Kei Hibino ex8k.hibino at gmail.com https://github.com/khibino/

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Call for concurrency bugs!
by Michael Walker 16 May '15

16 May '15

Hi cafe, I've been working on a little library for testing concurrent Haskell programs, and would really like some test cases not constructed by myself to throw it at. If anyone has any examples of buggy concurrency (preferably where it's tricky to provoke the bugs with conventional testing techniques) that I could use: either open bugs, or things which have been fixed but were awkward to do so, that would be really useful. This is leading up to a paper, hopefully, so examples may go into that: anonymously, if preferred. Thank you. -- Michael Walker (http://www.barrucadu.co.uk)

2 1

Deriving Show instance with ADT that has phantom type
by Cody Goodman 15 May '15

15 May '15

Going through the Data Types Ala Carte paper I found this definition: data Expr f = In (f (Expr f)) I tried to use "deriving Show"... data Expr f = In (f (Expr f)) deriving Show I found out that doesn't work with ADT's that have phantom types. I tried StandaloneDeriving too since GHC recommended it: {-# LANGUAGE StandaloneDeriving #-} data Expr f = In (f (Expr f)) deriving Show instance deriving Show (Expr f) Got this error: src/Main.hs:32:1-31: No instance for (Show (f (Expr f))) … arising from a use of ‘showsPrec’ In the second argument of ‘(.)’, namely ‘(showsPrec 11 b1)’ In the second argument of ‘showParen’, namely ‘((.) (showString "In ") (showsPrec 11 b1))’ In the expression: showParen ((a >= 11)) ((.) (showString "In ") (showsPrec 11 b1)) When typechecking the code for ‘showsPrec’ in a standalone derived instance for ‘Show (Expr f)’: To see the code I am typechecking, use -ddump-deriv Compilation failed. Here is the derived instance output from ghc -ddump-simple: Derived instances: instance GHC.Show.Show (Main.Expr f_aq1) where GHC.Show.showsPrec a_azP (Main.In b1_azQ) = GHC.Show.showParen ((a_azP GHC.Classes.>= 11)) ((GHC.Base..) (GHC.Show.showString "In ") (GHC.Show.showsPrec 11 b1_azQ)) GHC.Show.showList = GHC.Show.showList__ (GHC.Show.showsPrec 0) Didn't work. Can this be derived? Will I need to manually make instances?

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cast to specific Typeclass
by Teodor Vlasov 15 May '15

15 May '15

Hello everyone, I'm trying to implement traversal over data structures and found Data.Typeable very useful for that. But it seems to be impossible to cast to specific typeclass, so that we can cast Typeable to something that is Show'able for example. It'd be usefull to have something like: data CanShow = forall a. CanShow a toConcrete :: (Typeable a) => a -> Maybe CanShow Implementing such datatypes for needed classes would allow to do some kind of class casting. Is it possible to implement this somehow? Is it a limitation of the implementation or a principal one? Thanks! Regards, Teodor.

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