- Haskell-Cafe - Haskell.org

indentation with let and do
by Corentin Dupont 03 Oct '13

03 Oct '13

Hi the list, why do this function doesn't compile (parse error): test :: Bool -> IO () test foo = do let bar = case foo of True -> "Foo"; False -> "Bar" return () while this one does (just adding one space in front of True and False): test :: Bool -> IO () test foo = do let bar = case foo of True -> "Foo"; False -> "Bar" return () Thanks!! Corentin

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"plugins" fails on a simple example
by Petr Pudlák 03 Oct '13

03 Oct '13

Hi, I'm playing with "plugins", trying to evaluate a simple expression: |import Control.Monad import System.Eval.Haskell main =do let fExpr ="1 + 2 :: Int" r <- eval_ fExpr ["Prelude"] [] [] [] ::IO (Either [String] (Maybe Int)) case rof Right (Just f) ->do print $ f Left err -> putStrLn $"Error:" ++ unlines err _ -> putStrLn $"Unknown error."| However, it fails with |Error: on the commandline: Warning: -fglasgow-exts is deprecated: Use individual extensions instead| Am I doing something wrong? How can I turn off the flag? I'm using GHC 7.6.3. Thanks, Petr

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[ANN] lvish 1.0 -- successor to monad-par
by Ryan Newton 03 Oct '13

03 Oct '13

Hi all, I'm pleased to announce the release of our new parallel-programming library, LVish: hackage.haskell.org/package/lvish It provides a "Par" monad similar to the monad-par package, but generalizes the model to include data-structures other than single-assignment variables (IVars). For example, it has lock-free concurrent data structures for Sets and Maps, which are constrained to only grow monotonically during a given "runPar" (to retain determinism). This is based on work described in our upcoming POPL 2014 paper: http://www.cs.indiana.edu/~rrnewton/papers/2013_07_LVish_quasiDet_working_d… Cheers, -Ryan

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Re: [Haskell-cafe] Using lenses
by Niklas Haas 03 Oct '13

03 Oct '13

Another great use of lenses is the lens-aeson library (not to be confused with aeson-lens). It's technically based around prisms, though, so it's outside the scope of your talk; but you may wish to at least reference it - it makes working with JSON really elegant!

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Re: [Haskell-cafe] Using lenses
by Nicolas Trangez 03 Oct '13

03 Oct '13

Simon, On Thu, 2013-10-03 at 08:07 +0000, Simon Peyton-Jones wrote: > If you are using the lens library yourself, could you spare a few minutes to tell me how you are using it? I'm not a heavy 'lens'-user (yet), and this might not be the most pretty use-case from a theoretic point of view, but anyway: I use 'lens' in Kontiki [1], my implementation of Raft [2], a fairly recent consensus protocol for distributed systems (think Paxos & multi-Paxos, Zookeeper,...). The Raft protocol description is fairly imperative ("When in state S, if you receive a message M, broadcast message M'(M) to all other nodes, append entry E(M) to your log, and update the state to S'(S)"), so in order to keep the code close to this description, I created a TransitionT monad transformer (where the underlying monad should, in some cases, provide access to the persisted log of the system, most likely requiring IO access, but this is abstracted over), which is basically RWST. The R environment gives access to system configuration (e.g. the set of nodes (or at least their names/IDs) part of the cluster), W is used to output/list Commands to be executed as part of a state transition, S gives access to the current state, and a transition should yield a new state (or the old one if e.g. a message is received which should be ignored in the current state). See [3] for an overview of the types involved. Finally, after this long introduction, the 'lens' part: thanks to the 'lens' operators, and my types involved in the TransitionT monad (specifically the R environment and S state) being lens'ified, accessing R & S becomes fairly unobtrusive and more imperative-looking (which makes sense when using RWS). As an example, in [4], you see some parts of the current (Candidate) state being accessed: currentTerm <- use cCurrentTerm votes <- use cVotes Not using 'lens', this would be something (OTOH) like currentTerm <- fmap _cCurrentTerm get which is less familiar from an imperative POV. Then also updating the current state 'in-place' (not for real, obviously): cVotes %= Set.insert sender And accessing the configuration (R) environment, e.g.: nodeId <- view configNodeId See other handler functions in that module, or in the Follower and Leader modules in the same directory, for more examples. Regards, Nicolas [1] https://github.com/NicolasT/kontiki [2] https://ramcloud.stanford.edu/wiki/download/attachments/11370504/raft.pdf [3] https://github.com/NicolasT/kontiki/blob/master/src/Network/Kontiki/Types.hs [4] https://github.com/NicolasT/kontiki/blob/master/src/Network/Kontiki/Raft/Ca…

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[ANN] yi-0.7
by Dmitry Ivanov 03 Oct '13

03 Oct '13

I'm pleased to announce a new release of Yi, text editor written and extensible in Haskell. This release introduces new vim keybindings emulation. If all goes well, the old one will be deprecated in future. The advantages of the new emulation include support for visual block operations, more consistent repeat (dot command) behavior, lots of tests (but not nearly enough, because vim feature set is HUGE) and more. If you are a vim user, please try it out and help us make it better. Full changelog is available at https://github.com/yi-editor/yi/blob/v0.7/CHANGELOG Places to dicuss using and developing yi: mailing list: https://groups.google.com/group/yi-devel issue tracker: https://github.com/yi-editor/yi/issues IRC channel: #yi@freenode (it's very slow compared to #haskell, please don't quit after 10 mins) Regards, Dmitry

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Roshask
by Tijn van der Zant 02 Oct '13

02 Oct '13

Hi, I want to use Haskell to program my robot using ros. I've found roshask https://github.com/acowley/roshask and I was wondering if someone on this list has experience with it and can tell me how good it is. Thanx! --Tijn

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Haskell Logo Macbook Decal
by Ryan Trinkle 02 Oct '13

02 Oct '13

Hi everyone, I put together a Haskell logo decal designed to fit over the Apple logo on a MacBook, and had a few made by macdecals.com. They came out great! They're available here: http://www.macdecals.com/macbook-haskell . My share of the proceeds will go to haskell.org, and macdecals.com has generously offered to match that contribution, as well. Ryan

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Haskell.org design is broken
by Roman Cheplyaka 01 Oct '13

01 Oct '13

There is now a big white stripe in the Haskell.org's header (see the screenshot). Roman

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HTML framework for web-ui
by Vlatko Basic 01 Oct '13

01 Oct '13

Hi, I'd like to start using web pages as the UI for apps. I found out for yesod, snapp and happstack as the candidates. Would you recommend any of them as better for app ui (not "classical" web pages)? Or maybe another one? thanks, vlatko

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[ANN] fclabels 2.0
by Sebastiaan Visser 01 Oct '13

01 Oct '13

Hello everyone, I’m excited to announce a brand new major version of fclabels. This library provides first class labels that can act as bidirectional record fields. The labels are implemented as lenses. This new version contains some interesting new features like support for polymorphic updates and lens derivation for GADTs. Furthermore the API has been cleanup significantly and should be easier to work with. You can read everything about this release at: http://fvisser.nl/post/2013/okt/1/fclabels-2.0.html All feedback more than welcome! -Sebastiaan -- On Hackage: http://hackage.haskell.org/package/fclabels-2.0 Source on github: https://github.com/sebastiaanvisser/fclabels Full changelog: https://github.com/sebastiaanvisser/fclabels/blob/master/CHANGELOG

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The RTSOPTS "-qm" flag's impact on runtime
by Iustin Pop 01 Oct '13

01 Oct '13

Hi all, I found an interesting case where the rtsopts -qm flag makes a significant difference in runtime (~50x). This is using GHC 7.6.3, llvm 3.4, program compiled with "-threaded -O2 -fllvm" and a couple of language extension. Source is at http://benchmarksgame.alioth.debian.org/u64q/benchmark.php?test=chameneosre…, on the language shootout benchmarks. Running the code without -N results (on my computer) in around 4 seconds of runtime: $ time ./orig 6000000 … real 0m3.919s user 0m3.903s sys 0m0.010s This is reasonably consistent. Running -N4 (this is an 8-core machine) results in the surprising: $ time ./orig 6000000 +RTS -N4 … real 1m15.154s user 1m38.790s sys 2m7.947s The cores are all used very erratically (continuously changing 5%-20%-40%) and the overall cpu usage is ~27-28%. Note the surprising 2m7s of sys usage, which means the kernel is involved a lot… Note that removing the explicit forkOn and running with -N4 results in somewhat worse performance: real 2m6.548s user 2m13.470s sys 2m3.043s So in that sense the forkOn itself is not at fault. What I have found is that -qm is here a life saver: $ time ./orig 6000000 +RTS -N4 -qm real 0m2.773s user 0m5.610s sys 0m0.123s Adding -qa doesn't make a big difference. To summarise more runs (in terms of cpu used, user+sys): with forkOn: - -N4: 228s - -N4 -qa: 110s - -N4 -qm: 6s - -N4 -qm -qa: 6s without forkOn: - -N4: 253s - -N4 -qa: 252s - -N4 -qm: 5s - -N4 -qm -qa: 5s (Note that "without forkOn" is a bit slower in term of wall-clock, as the "with forkOn" version distributes the work a bit better, even if it uses overall a tiny bit more CPU.) So the question is, what does -qm actually do that it affects this benchmark so much (~50x)? (The docs are not very clear on it) And furthermore, could there be an heuristic inside the runtime such that automatic thread migration is suspended if threads are "over-migrated" (which is what I suppose happens here)? thanks for any explanations, iustin

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Proposal: Partitionable goes somewhere + containers instances
by Ryan Newton 30 Sep '13

30 Sep '13

<subject change> On Sun, Sep 29, 2013 at 3:31 AM, Mike Izbicki <mike(a)izbicki.me> wrote: > I've got a Partitionable class that I've been using for this purpose: > > https://github.com/mikeizbicki/ConstraintKinds/blob/master/src/Control/Cons… > Mike -- Neat, that's a cool library! Edward -- ideally, where in the standard libraries should the Partitionable comonoid go? Btw, I'm not sure what the ideal return type for comappend is, given that it needs to be able to "bottom out". Mike, our partition function's list return type seems more reasonable. Or maybe something simple would be this: *class Partitionable t where* * partition :: t -> Maybe (t,t)* That is, at some point its not worth splitting and returns Nothing, and you'd better be able to deal with the 't' directly. So what I really want is for the *containers package to please get some kind of Partitionable instances! * Johan & others, I would be happy to provide a patch if the class can be agreed on. This is important because currently the balanced tree structure of Data.Set/Map is an *amazing and beneficial property* that is *not* exposed at all through the API. For example, it would be great to have a parallel traverse_ for Maps and Sets in the Par monad. The particular impetus is that our new and enhanced Par monad makes extensive use of Maps and Sets, both the pure, balanced ones, and lockfree/inplace ones based on concurrent skip lists: http://www.cs.indiana.edu/~rrnewton/haddock/lvish/ Alternatively, it would be ok if there were a "Data.Map.Internal" module that exposed the Bin/Tip, but I assume people would rather have a clean Partitionable instance... Best, -Ryan On Sun, Sep 29, 2013 at 3:31 AM, Mike Izbicki <mike(a)izbicki.me> wrote: > I've got a Partitionable class that I've been using for this purpose: > > > https://github.com/mikeizbicki/ConstraintKinds/blob/master/src/Control/Cons… > > The function called "parallel" in the HLearn library will automatically > parallelize any homomorphism from a Partionable to a Monoid. I > specifically use that to parallelize machine learning algorithms. > > I have two thoughts for better abstractions: > > 1) This Partitionable class is essentially a comonoid. By reversing the > arrows of mappend, we get: > > comappend :: a -> (a,a) > > By itself, this works well if the number of processors you have is a power > of two, but it needs some more fanciness to get things balanced properly > for other numbers of processors. I bet there's another algebraic structure > that would capture these other cases, but I'm not sure what it is. > > 2) I'm working with parallelizing tree structures right now (kd-trees, > cover trees, oct-trees, etc.). The real problem is not splitting the > number of data points equally (this is easy), but splitting the amount of > work equally. Some points take longer to process than others, and this > cannot be determined in advance. Therefore, an equal split of the data > points can result in one processor getting 25% of the work load, and the > second processor getting 75%. Some sort of lazy Partitionable class that > was aware of processor loads and didn't split data points until they were > needed would be ideal for this scenario. > > On Sat, Sep 28, 2013 at 6:46 PM, adam vogt <vogt.adam(a)gmail.com> wrote: > >> On Sat, Sep 28, 2013 at 1:09 PM, Ryan Newton <rrnewton(a)gmail.com> wrote: >> > Hi all, >> > >> > We all know and love Data.Foldable and are familiar with left folds and >> > right folds. But what you want in a parallel program is a balanced fold >> > over a tree. Fortunately, many of our datatypes (Sets, Maps) actually >> ARE >> > balanced trees. Hmm, but how do we expose that? >> >> Hi Ryan, >> >> At least for Data.Map, the Foldable instance seems to have a >> reasonably balanced fold called fold (or foldMap): >> >> > fold t = go t >> > where go (Bin _ _ v l r) = go l `mappend` (v `mappend` go r) >> >> This doesn't seem to be guaranteed though. For example ghc's derived >> instance writes the foldr only, so fold would be right-associated for >> a: >> >> > data T a = B (T a) (T a) | L a deriving (Foldable) >> >> Regards, >> Adam >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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What class for splittable data / balanced-fold?
by Ryan Newton 30 Sep '13

30 Sep '13

Hi all, We all know and love Data.Foldable and are familiar with left folds and right folds. But what you want in a parallel program is a balanced fold over a tree. Fortunately, many of our datatypes (Sets, Maps) actually ARE balanced trees. Hmm, but how do we expose that? It seems like it would be nice to have a* standard class t*hat allows you to split a datatype into roughly even halves, until you get down to the leaves. This goes along with Guy Steele's argument that we should use "append lists" as primitive rather than "cons-lists", and it's why we added append-lists within the monad-par library<http://hackage.haskell.org/package/monad-par-extras-0.3.3/docs/Control-Mona…> . Does this class exist already? A random google search brought up this module by the name Data.Splittable<http://hackage.haskell.org/package/unfoldable-0.2.0/docs/Data-Splittable.ht…>, but it's not quite the right thing. Thanks, -Ryan

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Vacancy Assistant Professor Software Technology Utrecht University (1, 0 fte)
by Johan Jeuring 30 Sep '13

30 Sep '13

Assistant Professor Software Technology Utrecht University (1,0 fte) Job description The division Software Systems of the Department of Information and Computing Sciences is looking for an Assistant Professor for the bachelor programmes Computing Science and Information Science and the master programmes of the department, and for research in the area of software technology. You are expected to develop an independent line of research within the field of software technology in cooperation with the other members of the division Software Systems. The tasks include: performing scientific research in the field of software systems, in particular software technology; supervising PhD students and acquiring research funding; developing and teaching courses within the bachelor and master programmes of the department; supervising internships and theses; organizational activities within the division, department or faculty. Qualifications We are looking for candidates with a PhD with expertise and experience in scientific education and research in computer science. Expertise in the fields of software technology, programming languages and typing systems, advanced programming methods, or compilers is required. Experience in academic education within a university setting is desired. You have published on the aforementioned areas in national and international conferences and / or journals. Well-developed teaching skills and command of English in speaking and writing are a requirement. Candidates who prefer part-time employment are also invited to apply by specifying the desired part-time ratio. Offer We offer a position in a dynamic environment. The position is for at most five years. The total size of the position is 100%, but part-time is possible. The salary depends on education and experience and ranges between € 2,919 (scale 10) and € ,5070 (scale 12) gross per month for a full-time appointment. Additionally, excellent secondary benefits are provided, such as 8% holiday allowance and 8.3% end of year bonus. We also offer a pension scheme, partially paid parental leave and flexible working conditions. For more information see the terms of employment. The department provides the candidate the necessary support for the arrangements of the education and research line. About the organisation Utrecht University has great ambitions for its teaching quality and study success rates. This also applies to its clear research profiles which are centred around four themes: Sustainability, Life Sciences, Youth & Identity, and Institutions. Utrecht University plays a prominent role in our society and contributes to finding the answers to topical and future societal issues. The Faculty of Science at Utrecht University comprises six departments: Biology, Pharmacy, Information and Computer Sciences, Chemistry, Mathematics and Physics and Astronomy. It has 3500 students and nearly 2000 employees, and is internationally known for its quality in research. The academic programs of the Faculty reflect developments in society and science of today. The Department of Information and Computer Science is nationally and internationally renowned for its fundamental research in computer science and information science. Its research is positioned around game technology, one of the four research themes of the Faculty of Science. The research of the department is grouped into four divisions: Software Systems, Artificial Intelligence, Virtual Worlds and Interaction Technology. The Department offers bachelor programmes in computer science and information science, and four English-language research master-programmes including Computing Science. High enrollment figures and good student ratings make the education very successful. Part of the research of the division Software Systems focuses on how programming languages, methods, and tools can be adapted to support program construction. More specifically, the research covers the following areas: programming languages and compiler construction-tools program analysis interaction analysis, error diagnosis advanced programming methods: generic programming, dependently-typed programming program testing and verification The division aims to design better programming languages and methods; to implement tools and languages that help programmers work more effectively; and to develop products and systems demonstrating the feasibility (and/or validity) of the ideas. An important application area studied in the department and the division is (serious) games. The division mainly contributes to the education in the bachelor programs information science and computer science, and to the master program Computing Science. Additional information For more information please contact Prof.dr. Johan Jeuring +31.30.253.4115 or +31.6.400.100.53, email:J.T.Jeuring@uu.nl. Apply Your application must contain a letter of motivation, your CV with publication list, teaching and research statement, and contact details of at least two references. You can respond via the application button below. The application deadline is 21/10/2013 Assistant Professor Software Technology (1,0 fte)

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New Functional Programming Job Opportunities
by Functional Jobs 30 Sep '13

30 Sep '13

Here are some functional programming job opportunities that were posted recently: Senior Scala Developer for Green Building Software at Sefaira http://functionaljobs.com/jobs/8649-senior-scala-developer-for-green-buildi… Cheers, Sean Murphy FunctionalJobs.com

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FFI: how to handle external dll crashes
by Miro Karpis 30 Sep '13

30 Sep '13

Please, can you help me with following: I have an external dll that I'm importing in my haskell program. In some particular cases the dll crashes. Simplified: first I need to send to dll with MethodA some parameters and then call MethodB to do some calculations on those parameters. If I didn't give enough parameters then MethodB will crash the whole dll and my Haskell application. Is there a way to handle this? Unfortunately there are no exceptions thrown from the dll. In ghci I'm getting following message: ERROR in InitNumericalSystem::initializeSystem. JuncLabel. I have tried to use "catchAny but that didn't help. c_run is my external dll method which takes 4 input parameters: catchAny :: IO a -> (SomeException -> IO a) -> IO a catchAny = Control.Exception.catch main :: IO () main = do let timeTot = []::[CDouble] timeNow = []::[CDouble] runType = 2::CInt timeTotPtr <- newArray timeTot timeNowPtr <- newArray timeNow result <- (catchAny $ c_run timeTotPtr runType timeNowPtr 0) $ \e -> do putStrLn $ "Got an exception: " ++ show e putStrLn "Returning dummy value of -1" return (-1) free timeTotPtr free timeNowPtr print result I have tried also with withAsync, and no luck tryAny :: IO a -> IO (Either SomeException a) tryAny action = withAsync action waitCatch catchAny :: IO a -> (SomeException -> IO a) -> IO a catchAny action onE = tryAny action >>= either onE return try2 :: IO () try2 = do let timeTot = []::[CDouble] timeNow = []::[CDouble] runType = 2::CInt timeTotPtr <- newArray timeTot timeNowPtr <- newArray timeNow putStrLn $ "c_run going to call c_run.." result <- catchAny (c_run timeTotPtr runType timeNowPtr 0) (const $ return (-1)) free timeTotPtr free timeNowPtr putStrLn $ "Result: " ++ show result Is there a way how I can handle this? cheers, m.

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Richard Bird and the fast nub function
by Henning Thielemann 30 Sep '13

30 Sep '13

In Richard Bird's "Functional Pearls in Algorithm Design" there is chapter 10 "Removing duplicates" which is about a fast and sorting variant of 'nub'. After reading the introduction of the chapter I answered mentally "Set.toAscList . Set.fromList - next chapter please". However after the introduction eight pages follow that develop an efficient algorithm for the problem. I suspected there might be the additional difficulty of not using the standard Set type, however on page 70 the common Set API is "imported". In the final remarks of the chapter Bird writes: "A nagging doubt remains that there might be a much simpler solution to such a simply stated problem. But so far I have not been able to find one." Now I am lost. Can someone tell me, how the task differs from what "Set.toAscList . Set.fromList" does?

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[ANN] New OpenCV Bindings
by Arjun Comar 29 Sep '13

29 Sep '13

Hi all, I've been hard at work on a new set of OpenCV bindings that will hopefully solve a lot of the shortcomings with previous attempts. An automatic header parser has been used to generate a full set of Haskell bindings for the C++ API, and I'm now working to create a pleasant Haskell API. The plan is to expose major functionality through pipes for two reasons: 1) OpenCV is not very referentially transparent, and so you're stuck in IO for anything non-trivial. Lazy IO is potentially problematic, and so immediate incorporation of a proper streaming library is probably best. 2) Computer vision algorithms are frequently expressed in terms of pipelines of functionality, and a pipes approach can provide a very natural API for expressing these algorithms. At this stage, I could very much use input from anyone who's interested in these bindings. I've got the basics of a library forming, but there's a ton to do and help in the form of pull requests are very very welcome. I could also use feedback on what's been done so far (especially criticisms) as well as feature requests. The current plan is to develop the pipes API for the core functionality. The plan is to provide the major functionality from core, highgui, imgproc, features2d, contrib, ml, flann, video, and objdetect as quickly as I can before trying to cover any of the more specialized parts of the API. The functions and types from these modules (baring a few major and important exceptions) are automatically translated into C wrappers and raw Haskell bindings. If there's sufficient interest in these raw bindings separately from the API I'm developing, I'll release them as a separate package on Hackage. I'm calling my project revelation for the moment because I'm bad at naming things and it was the best pun I could come up with. Github: www.github.com/arjuncomar/revelation Regards, Arjun

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Proposal: new function for lifting
by Thiago Negri 29 Sep '13

29 Sep '13

Everybody is claiming that using lift is a bad thing. So, I come to remedy this problem. Stop lifting, start using shinny operators like this one: (^$) :: Monad m => m a -> (a -> b -> c) -> m b -> m c (^$) = flip liftM2 Then you can do wonderful stuff and you will never read the four-letter word in your code again: \> Just 42 ^$(+)$ Nothing Nothing \> Just 10 ^$(+)$ Just 20 Just 30 \> let add = (+) \> Just 30 ^$ add $ Just 12 Just 42

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Fwd: [GSoC 2013] Porting Charts to Diagrams - Final Report
by Jan Bracker 29 Sep '13

29 Sep '13

Hello everybody, I am sorry to send this a second time. Someone hinted out that I would not reach everybody on the mailing list through the Google Groups address. I should have looked a bit more thoroughly. The Google Summer of Code 2013 is over! My project to port the charts [0] library to use diagrams [1] as an alternative to cairo [2] was a full success. The project goal [3,4] was to remove cairo as a dependency and replace it with a open backend API so different technologies can be used to render charts. This was mainly necessary, because cairo is hard to install on platforms like windows or mac. Aside of that it also makes charts more flexible and opens the doors for renderings charts in different contexts. We were successful. The cairo rendering code was completely removed from the chart library and replaced by a drawing API [5] that is backend independent. The cairo rendering backend, of course, is still there and now provided as the separate package Chart-cairo [6]. In addition we implemented a second backend based on the diagrams library. It is provided in Chart-diagrams [7]. To give some more detail on the development: The backend API is now based on a deep embedding of all drawing commands in the ChartBackend monad. The sequence of drawings commands resulting from this is then interpreted by a implementing backend. We use the operational package [9] to implement the deep embedding. Implementing the cairo backend was straightforward, because the backend API was developed with the cairo API in mind. Implementing the diagrams backend was some more work. Drawing on its own is not a problem but calculating text metrics is, because it requires to access the systems font rendering capabilities most of the time. Diagrams does not offer this access for several reasons (missing backend support, unclear how API would look, etc.). You can look at the diagrams-discuss mailing list for further information on this topic. We used the SVGFonts [10] library to render fonts, because of these issues. It is independent of the used backend and uses the SVGFonts format to render fonts and calculate their metrics. Like this fonts can be preloaded and metrics can be calculated on the fly. The only downside of this approach is that its performance is not to good, because we render each glyph as a path and because the math done in diagrams is not to fast either. At least when rendering to SVG files we could improve the performance by embedding fonts into the produced SVG and by that saving to insert each glyph as a path. The API to access this is not yet on hackage but the new version will be released soon. You can look at the GitHub repository [11] if you want to access it. Along with this development I also had the change to tackle some bugs and improve the diagrams-svg [12] and SVGFonts [10] code. Everybody who is interested in the details of the development process and see every bit of what was done can check the chart or diagrams mailing list. Both contain the progress reports of the project [8]. So have a look at charts [0] and see what it can do. We also have a nice little tutorial on how to use the new backends [13]. Greets Jan [0]: https://github.com/timbod7/haskell-chart/wiki [1]: http://projects.haskell.org/diagrams/ [2]: http://hackage.haskell.org/package/cairo [3]: http://www.google-melange.com/gsoc/proposal/review/google/gsoc2013/jbracker… [4]: http://www.google-melange.com/gsoc/project/google/gsoc2013/jbracker/33001 [5]: http://hackage.haskell.org/packages/archive/Chart/1.0/doc/html/Graphics-Ren… [6]: http://hackage.haskell.org/package/Chart-cairo [7]: http://hackage.haskell.org/package/Chart-diagrams [8]: https://groups.google.com/d/topic/diagrams-discuss/S2nkxyxbtcY/discussion [9]: http://hackage.haskell.org/package/operational [10]: http://hackage.haskell.org/package/SVGFonts [11]: https://github.com/timbod7/haskell-chart/blob/master/chart-diagrams/Graphic… [12]: http://hackage.haskell.org/package/diagrams-svg [13]: https://github.com/timbod7/haskell-chart/wiki/How-to-use-backends

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Munich Haskell Meeting, 2nd birthday
by Heinrich Hördegen 28 Sep '13

28 Sep '13

Dear all, I am pleased to announce that our monthly Haskell meeting is scheduled on Monday, 30th of September, 19h30 at Cafe Puck. If you plan to join, please click the button at: http://www.haskell-munich.de/dates Our monthly meetings started on Thu, 29 Sept 2011, so this will be over two years now! With hope to coninue in this nice and friendly sprit, Heinrich

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Re: [Haskell-cafe] Proposal: new function for lifting
by Nick Vanderweit 28 Sep '13

28 Sep '13

Sorry for sending this twice; I didn't reply to the list initially. I thought people [1] were generally talking about lift from Control.Monad.Trans: class MonadTrans t where lift :: Monad m => m a -> t m a The idea being that lifting through a monad stack feels tedious. The proposed solution is to use instances to do the lifting for you, like in mtl. So we've got instances like: MonadState s m => MonadState s (ReaderT r m) Which let you automatically lift get/put/modify up a stack, without doing any work. This is different from liftM*, which are about applying a pure function to monadic arguments. This can be done quite nicely with (<$>) and (<*>) from Data.Functor and Control.Applicative, respectively. Your first example can be written: (+) <$> (Just 42) <*> Nothing Nick [1] http://blog.ezyang.com/2013/09/if-youre-using-lift-youre-doing-it-wrong-pro…

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Non-termination using Free Monads and Data Types a la Carte
by Alexander Solla 27 Sep '13

27 Sep '13

I am trying to use a data types a la carte approach to define a free monad for templating purposes. I am using Edward Kmett's free package, and a module implementing data types a la carte's injections, modelled on the IOSpec Types module. I have written a few combinators, but I am stuck. My program keeps diverging, and I don't see why. Consider: math :: Math :<: f => MathExpr a -> Free f () blank :: f :<: (Textual :+: Math) => Free f () -> Free (Blank k f) () equals :: Free (Math :+: (Blank L Math)) () -> Free (Math :+: (Blank R Math)) () -> Free Equation () The intention is that a blank takes in a properly typed abstract syntax tree and tags it with "blank k", so that the parsers/renderers do the "right thing" (when I get around to implementing them) The composition (blank . math) has the type: blank . math :: ( f :<: (Textual :+: Math) , Math :<: f ) => MathExpr a -> Free (Blank k f) () Notice that f must be simultaneously less than or equal to the join of Textual and Math, and greater than or equal to Math. So the only possibility for f is Math. (I realize the compiler can't infer this without more work on my part) The problem happens when I try to evaluate (using scoped type signatures to get around my comment above): test :: Free Equation () test = (hoistFree (inj :: Blank 'L Math a -> (Math :+: Blank 'L Math) a) . blank . (math :: MathExpr x -> Free Math ()) $ "hi" ) `equals` (math $ "world") which apparently loops, pegging my CPU at 100%. The computation prints its result as: Free (Equation (Free (DirectSum {unDirectSum = Right at which point the value is truncated and GHCi quits. So it apparently gets as far as figuring out that the first argument to equals is in the latter part of the direct sum, but it doesn't seem t be able to compute blank. Relatively minimal source is available at: monad: http://lpaste.net/93471 data types a la carte: http://lpaste.net/93472 All my functions are total and I don't see a bottom here, but I was never any good at fixed point combinators. Any ideas?

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[ANNOUNCE] cereal-0.4.0.0
by Trevor Elliott 27 Sep '13

27 Sep '13

Hi Everyone, I'm happy to announce the newest release of the cereal[1] binary serialization library. This includes a number of bug fixes, as well as instances of Serialize for the newtypes defined in Data.Monoid. Happy hacking! --trevor [1] http://hackage.haskell.org/package/cereal-0.4.0.0

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Proposal: RankedInstances
by Wvv 27 Sep '13

27 Sep '13

The main power of Haskell is on instances. But Haskell instances system work fine with lower number of instances (rare instances). But we want hight density of instances! If we wish to have more selective instances we use `OverlappingInstances` (which are desined in a poor way) and if we still have too many instances we use `IncoherentInstances`. ~~`RankedInstances` extension ~~ I suggest simple `RankedInstances` extension. We use it (!)before OverlappingInstances (it must include `RankedInstances`), and in many cases instead of. This extension is easy to implement and it give us a lot of new possibilities and instruments. Now the system of instances is flat, and compiler takes all of them and check if only 1 match. If it is not(less or more than) - compiler trow an error. I suggest to add rankings, so compiler * compiler set N=0 * took all N-ranked instances and ** try to find only one match instance. *** If it found 1 - this is RESULT: needed instance, *** If it found many instances - still throw an error ******* (then we use `OverlappingInstances` to resolve this) *** If compiler found NO instances, compiler set N=N+1 and repeat * If N=MaxRank and still no matches compiler throw an error ~~How to add a rank~~ I suggest next grammar: {-# LANGUAGE RankedInstances #-} instance rank 1. C a => D a where ... instance C2 a => E a where ... <<==>> instance rank 0. C2 a => E a where ... So, all written instances(without ranking) are 0-ranked instances. Backward compatibility => without -XRankedInstances all instances with rank n, where n >0 - are not exported ~Example~ 1) instance rank 1. C Int a where ... -- (A) instance C a Bool where ... -- (B) rank 0 1+) instance rank 1. C Int a where ... -- (A) instance rank 1. C a Bool where ... -- (B) instance C Int Bool where ... -- (C) rank 0 2) instance rank 1. C Int [a] where ... -- (C) instance C Int [Int] where ... -- (D) As we see, all instances are unambiguous! ~~ Rank Scale~~ It is for discussion, I see this like: 0 - default 1 ..9 - user free (without fear to overlap with devs instances) 10 .. 14 - Generic 15 .. - superclass' instances ~~ Higher Rank instances~~ We don't need to use `default` inside of class: instance rank 10. (Generic a, GToJSON (Rep a)) => ToJSON a where toJSON = genericToJSON defaultOptions We could add superclass' instances now, something like these: instance rank 15. Monad m => Applicative m where pure = return (<*>) = ap instance rank 16. Monad m => Functor m where fmap = liftM instance rank 17. Applicative m => Functor m where fmap f x = pure f <*> x ~~Inherit mechanism~~ What do if we want to use any proposed instance, not in the rank order ? For example we have data, which is Monad and Applicative, but not a Functor. We'll use automatically "instance rank 16. Monad m => Functor m", but not "instance rank 17. Applicative m => Functor m" . But we wish to use the last one. We need to create a new instance and inherit the behavior of needed instance data D a .... instance Monad D where ... instance Applicative D where ... instance rank 1. Functor D inherit (D ~ m) instance Applicative m => Functor m foo = ... fmap So, in this case we'll use `fmap` as Applicative Functor. Inherit mechanism defaulting : instance C a => D a where ... <<==>> instance C a => D a inherit (a ~ b) class D b where ~~ "As" pattern in RankedInstances~~ Now we add "as" pattern and rewrite both of our instances: instance rank 17. Applicative m => ApFunctor@Functor m where fmap f x = pure f <*> x instance ApFunctor D --by the way 0-ranked Wow!!! It is simple, safe and looks nicer! ~~Partly Applied Instances~~ We describe a situation when we write a child class and want automatically get access to parent's classes. But sometimes we need to use already defined parent classes to describe children classes We CANNOT do next: instance rank 20. (Functor m, Applicative m) => Monad m where ma >> mb = (fmap (const id) ma) `apply` mb instance rank 21. Applicative m => Monad m where ma >> mb = (pure (const id) <*> ma) `apply` mb Because if we define data D a ... instance Functor D ... instance Applicative D ... D a >>= D b -- this will compiler, but we have no full applied MonadInstance How to resolve this? I suggest to add one reserved world "newclass" (as an analog of newtype) --instance (Functor m, Applicative m) => FAMonad@Monad m where newclass (Functor m, Applicative m) => FAMonad@Monad m where ma >> mb = (fmap (const id) ma) `apply` mb --instance Applicative m => AMonad@Monad m where newclass (Applicative m) => AMonad@Monad m where ma >> mb = (pure (const id) <*> ma) `apply` mb The "newclass" is just an instance, but guarded - compiler did count it when it try to match So, now next throw an error: D a >>= D b And we have an ability to write more precisely instance AMonad H where instance FAMonad K where ~~~BIG Example~~~~ Let try to divide "class (Eq a)=>Ord a" to both: ORIGINAL ONE: class (Eq a) => Ord a where compare :: a -> a -> Ordering ... compare x y = if x == y then EQ else if x <= y then LT else GT Proposed one (it is just an example, not a "real" proposal): class Ord' a where ........... compare x y = if x < y then LT else if x > y then GT else EQ -- without Eq it is a last choice newclass (Eq a) => Ord@Ord' a where compare x y = if x == y then EQ else if x <= y then LT else GT So now we have both Ord' a for nonEQ data and for Eq data. And this has a backward compatibility! -- View this message in context: http://haskell.1045720.n5.nabble.com/Proposal-RankedInstances-tp5737152.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Looking for numbers to support using haskell
by Mike Meyer 27 Sep '13

27 Sep '13

Hi all, I'm looking for articles that provide some technical support for why Haskell rocks. Not just cheerleading, but something with a bit of real information in it - a comparison of code snippets in multiple languages, or the results of a study on programmer productivity (given all the noise and heat on the topic of type checking, surely there's a study somewhere that actually provides light as well), etc. Basically, I'd love things that would turn into an elevator pitch of "I can show you how to be X times more productive than you are using Y", and then the article provides the evidence to support that claim. Thanks, Mike

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Why superclass' instances are bad idea?
by Wvv 27 Sep '13

27 Sep '13

I suggest to add superclass' instances into libraries. http://ghc.haskell.org/trac/ghc/ticket/8348 In brief, we could write next: >{-# LANGUAGE FlexibleInstances #-} >{-# LANGUAGE UndecidableInstances #-} > >instance Monad m => Applicative m where > pure = return > (<*>) = ap > >instance Monad m => Functor m where > fmap = liftM > >instance Monad m => Bind m where > (>>-) = flip (>>=) > B.join = M.join this code is valid! I've already defined 3 "superclassses" for Monad: Functor, Applicative and Bind! Similar idea said Edward Kmett in 2010 (founded by monoidal) ( http://stackoverflow.com/questions/3213490/how-do-i-write-if-typeclass-a-th… ) And he said "but effectively what this instance is saying is that every Applicative should be derived by first finding an instance for Monad, and then dispatching to it. So while it would have the intention of saying that every Monad is Applicative (by the way the implication-like => reads) what it actually says is that every Applicative is a Monad, because having an instance head 't' matches any type. In many ways, the syntax for 'instance' and 'class' definitions is backwards." Why? I don't understand. Not every Applicative is a Monad, but every Monad is Applicative -- View this message in context: http://haskell.1045720.n5.nabble.com/Why-superclass-instances-are-bad-idea-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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FP Complete competition clarification
by Mike Meyer 26 Sep '13

26 Sep '13

I got some clarification on what "unpublished" means for FP Complete competition entries. Basically, you can enter code that you've already published, providing it has an appropriate license (or can be republished with such a license). The tutorial/description/documentation that shows how to use it must be unpublished. So, if you're looking for a good excuse to document an existing project, how about a chance to win $1000 by doing so?

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Hackage 2 switchover imminent
by Duncan Coutts 26 Sep '13

26 Sep '13

Hi everyone, Having been running the Hackage 2 alpha & beta for several months we intend to do the final switchover tomorrow (Wednesday 25th Sept). This will involve disabling uploads to the old server for a few hours. If all goes well we will switch the DNS over. If anything goes wrong we will just re-enable the old server. After the switch, everyone with a hackage account will need to do a one-time self-service account upgrade. A small handful of hackage early adopters will need assistance from an administrator to upgrade their accounts. We will email these people individually with instructions. If you wish to help or keep an eye on the switchover process then you are welcome to join us on the #hackage IRC channel on Freenode. If you run into problems after the switch there are site administrators you can contact and there is an issue tracker. Please report bugs in the site issue tracker: https://github.com/haskell/hackage-server/issues For issues with accounts or permissions please contact the administrators by email at admins(a)hackage.haskell.org -- Duncan Coutts, Haskell Consultant Well-Typed LLP, http://www.well-typed.com/

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Re: [Haskell-cafe] [GSoC 2013] Porting Charts to Diagrams - Final Report
by Daniel Santa Cruz 26 Sep '13

26 Sep '13

Awesome work, Jan. I'm looking forward to playing around with the new libs! As a side note, what did you use to generate your email? Did you manage all the footnotes by hand? Daniel

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Haskell Job Opportunity (Remote Work)
by Benny 26 Sep '13

26 Sep '13

Hello, ShotVibe is an early-stage Israeli startup company in the mobile photo sharing space. We are looking for an experienced or expert level Haskell programmer for backend web related projects. The work will be done by you remotely, using a freelancer model, with the potential for longer term work in the near future (also remote). One of the projects we have is a server application that queues messages that are to be sent to end user mobile phones, and pushes them through the "push notification" APIs supplied by Google and Apple. The work needed here involves some bug fixes, and some new features. This project will likely eventually be open sourced. Another project that we need to be written from scratch is a web application that handles photo uploads and processes them (including verifying user authentication with our main web backend, image resizing, and storing images on Amazon S3). This will probably end up only a few hundred lines of Haskell code, but involves integrating a bunch of stuff together. We are also interested in experimenting in using Haskell for some other areas of our backend where we are currently using Python. If you are interested you may contact me at: benny(a)shotvibe.com Please feel free to forward this email to any friends or acquaintances that may be interested.

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Haskell Weekly News: Issue 281
by Daniel Santa Cruz 26 Sep '13

26 Sep '13

Welcome to issue 281 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of September 15 to 21, 2013. Quotes of the Week * jmcarthur: weak algebraic structures? ha! i prefer my algebraic structures to put up more of a fight. * newsham: teach a man to pred and he will pred to zero. teach a man to succ and he will succ forever Top Reddit Stories * Edward C++Hands Domain: bartoszmilewski.com, Score: 83, Comments: 102 On Reddit: [1] http://goo.gl/64LLo4 Original: [2] http://goo.gl/0H0yr7 * Perfect streaming using `pipes-bytestring` Domain: haskellforall.com, Score: 59, Comments: 45 On Reddit: [3] http://goo.gl/oSlzZP Original: [4] http://goo.gl/8xwZjc * Adding safe coercions to Haskell Domain: joachim-breitner.de, Score: 58, Comments: 23 On Reddit: [5] http://goo.gl/2vs5M9 Original: [6] http://goo.gl/n0RYA3 * Which programming languages do you like besides Haskell, and why? Domain: self.haskell, Score: 55, Comments: 104 On Reddit: [7] http://goo.gl/nzgwJQ Original: [8] http://goo.gl/nzgwJQ * GHC HEAD: merged checkable "minimal complete definitions" (#7633) Domain: ghc.haskell.org, Score: 48, Comments: 36 On Reddit: [9] http://goo.gl/VoZVYL Original: [10] http://goo.gl/5F61AX * Do companies ever hire someone who has no Haskell experience to be a Haskell programmer? If I pursue such a job, how important would a Domain: self.haskell, Score: 44, Comments: 50 On Reddit: [11] http://goo.gl/KA998k Original: [12] http://goo.gl/KA998k * [Haskell-cafe] PSA: do not install xcode 5 if you are using ghc 7.6 Domain: haskell.org, Score: 43, Comments: 4 On Reddit: [13] http://goo.gl/ut6k6p Original: [14] http://goo.gl/1G8Syo * Model Analysis - The New York Times’ Erik Hinton breaks down a Fashion Week special Domain: source.mozillaopennews.org, Score: 40, Comments: 4 On Reddit: [15] http://goo.gl/NdVw6l Original: [16] http://goo.gl/bYB8JS * Programming reactively with both barrels (experiences of Haskell/FRP for mobile games) Domain: blog.reactiveprogramming.org, Score: 39, Comments: 7 On Reddit: [17] http://goo.gl/QXacUo Original: [18] http://goo.gl/wLJwt6 * Why monads have not taken the Common Lisp world by storm [r/lisp] Domain: reddit.com, Score: 33, Comments: 14 On Reddit: [19] http://goo.gl/tZUVWx Original: [20] http://goo.gl/w5KHqc * 13,000 readers Domain: self.haskell, Score: 28, Comments: 11 On Reddit: [21] http://goo.gl/lTys0R Original: [22] http://goo.gl/lTys0R * A type for IO actions that do not throw exceptions Domain: self.haskell, Score: 25, Comments: 49 On Reddit: [23] http://goo.gl/Ao8HyB Original: [24] http://goo.gl/Ao8HyB * ANN: Scotty 0.5.0 Released Domain: github.com, Score: 24, Comments: 15 On Reddit: [25] http://goo.gl/jgGJhO Original: [26] http://goo.gl/BejPTF * Haskell version freezing Domain: blog.docmunch.com, Score: 23, Comments: 8 On Reddit: [27] http://goo.gl/9LJSjY Original: [28] http://goo.gl/Ikd86k * PHOAS For Free by Edward Kmett Domain: fpcomplete.com, Score: 21, Comments: 8 On Reddit: [29] http://goo.gl/RDt1BV Original: [30] http://goo.gl/o0phN7 * Cellular Automata, Part III by Edward Kmett Domain: fpcomplete.com, Score: 20, Comments: 0 On Reddit: [31] http://goo.gl/AKCfGw Original: [32] http://goo.gl/x7GtH1 * Translating Haskell programs to Coq [/Gallina] programs Domain: github.com, Score: 20, Comments: 2 On Reddit: [33] http://goo.gl/IQAp3K Original: [34] http://goo.gl/qcib77 * ANN: pipes-csv: a fast, streaming csv parser based on cassava and pipes Domain: github.com, Score: 20, Comments: 9 On Reddit: [35] http://goo.gl/aITtGX Original: [36] http://goo.gl/yrzZ7n Top StackOverflow Questions * What does the “Just” syntax mean in Haskell? votes: 12, answers: 4 Read on SO: [37] http://goo.gl/f17UEP * How can I understand “:t ((==) <*>)” in haskell? votes: 10, answers: 1 Read on SO: [38] http://goo.gl/CwyBn4 * why polymorphism is so costly in haskell(GHC)? votes: 10, answers: 3 Read on SO: [39] http://goo.gl/4MjcbH * Break and continue in GHCi debugger without use of breakpoints votes: 9, answers: 0 Read on SO: [40] http://goo.gl/HrtcXZ * Why is there no `-XDeriveApplicative` extension? votes: 8, answers: 1 Read on SO: [41] http://goo.gl/4dcRF1 * Downsides to ScopedTypeVariables votes: 7, answers: 2 Read on SO: [42] http://goo.gl/UjBcsg * Haskell design encompassing several monads votes: 7, answers: 1 Read on SO: [43] http://goo.gl/EwWd5d * How to correct my OOP tendencies when programming in Haksell votes: 7, answers: 3 Read on SO: [44] http://goo.gl/9JVqh7 * composing functions with higher arity votes: 7, answers: 5 Read on SO: [45] http://goo.gl/jQjNJW * Why are Haskell Maps implemented as balanced binary trees instead of traditional hashtables? votes: 7, answers: 3 Read on SO: [46] http://goo.gl/nZaLGV Until next time, [47]+Daniel Santa Cruz References 1. http://bartoszmilewski.com/2013/09/19/edward-chands/ 2. http://www.reddit.com/r/haskell/comments/1mqni1/edward_chands/ 3. http://www.haskellforall.com/2013/09/perfect-streaming-using-pipes-bytestri… 4. http://www.reddit.com/r/haskell/comments/1msinm/perfect_streaming_using_pip… 5. http://www.joachim-breitner.de/blog/archives/610-Adding-safe-coercions-to-H… 6. http://www.reddit.com/r/haskell/comments/1mfz8z/adding_safe_coercions_to_ha… 7. http://www.reddit.com/r/haskell/comments/1mvb2e/which_programming_languages… 8. http://www.reddit.com/r/haskell/comments/1mvb2e/which_programming_languages… 9. http://ghc.haskell.org/trac/ghc/ticket/7633#comment:28 10. http://www.reddit.com/r/haskell/comments/1mp434/ghc_head_merged_checkable_m… 11. http://www.reddit.com/r/haskell/comments/1mtcox/do_companies_ever_hire_some… 12. http://www.reddit.com/r/haskell/comments/1mtcox/do_companies_ever_hire_some… 13. http://www.haskell.org/pipermail/haskell-cafe/2013-September/108902.html 14. http://www.reddit.com/r/haskell/comments/1ml97r/haskellcafe_psa_do_not_inst… 15. http://source.mozillaopennews.org/en-US/learning/model-analysis/ 16. http://www.reddit.com/r/haskell/comments/1mlgwd/model_analysis_the_new_york… 17. http://blog.reactiveprogramming.org/?p=107 18. http://www.reddit.com/r/haskell/comments/1moob5/programming_reactively_with… 19. http://www.reddit.com/r/lisp/comments/1mkqvj/why_monads_have_not_taken_the_… 20. http://www.reddit.com/r/haskell/comments/1mn6vb/why_monads_have_not_taken_t… 21. http://www.reddit.com/r/haskell/comments/1modra/13000_readers/ 22. http://www.reddit.com/r/haskell/comments/1modra/13000_readers/ 23. http://www.reddit.com/r/haskell/comments/1mpsvj/a_type_for_io_actions_that_… 24. http://www.reddit.com/r/haskell/comments/1mpsvj/a_type_for_io_actions_that_… 25. https://github.com/xich/scotty/blob/master/ReleaseNotes.md 26. http://www.reddit.com/r/haskell/comments/1mr9hf/ann_scotty_050_released/ 27. http://blog.docmunch.com/blog/2013/haskell-version-freezing 28. http://www.reddit.com/r/haskell/comments/1mjldi/haskell_version_freezing/ 29. https://www.fpcomplete.com/user/edwardk/phoas 30. http://www.reddit.com/r/haskell/comments/1mo59h/phoas_for_free_by_edward_km… 31. https://www.fpcomplete.com/user/edwardk/cellular-automata/part-3 32. http://www.reddit.com/r/haskell/comments/1mfaqx/cellular_automata_part_iii_… 33. https://github.com/gdijkstra/hs-to-gallina/blob/master/docs/report/report.p… 34. http://www.reddit.com/r/haskell/comments/1miawm/translating_haskell_program… 35. https://github.com/jb55/pipes-csv 36. http://www.reddit.com/r/haskell/comments/1mvbk7/ann_pipescsv_a_fast_streami… 37. http://stackoverflow.com/questions/18808258/what-does-the-just-syntax-mean-… 38. http://stackoverflow.com/questions/18813431/how-can-i-understand-t-in-haske… 39. http://stackoverflow.com/questions/18854866/why-polymorphism-is-so-costly-i… 40. http://stackoverflow.com/questions/18876128/break-and-continue-in-ghci-debu… 41. http://stackoverflow.com/questions/18861231/why-is-there-no-xderiveapplicat… 42. http://stackoverflow.com/questions/18852341/downsides-to-scopedtypevariables 43. http://stackoverflow.com/questions/18866558/haskell-design-encompassing-sev… 44. http://stackoverflow.com/questions/18867620/how-to-correct-my-oop-tendencie… 45. http://stackoverflow.com/questions/18905867/composing-functions-with-higher… 46. http://stackoverflow.com/questions/18908639/why-are-haskell-maps-implemente… 47. https://plus.google.com/105107667630152149014/about

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Haskell Weekly News: Issue 280
by Daniel Santa Cruz 25 Sep '13

25 Sep '13

Welcome to issue 280 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of September 8 to 14, 2013. Quotes of the Week * haasn: edwardk uses things in anger. shachaf uses them with disappointment :( * shachaf: Are you reading Mac Lane now? Saizan: yeah, it's not so bad if you skip the examples Top Reddit Stories * For my 17th birthday, my best friend got me "The most obscure programming book I could find" as a joke. I know what language I am learning next! Domain: i.imgur.com, Score: 163, Comments: 67 On Reddit: [1] http://goo.gl/0SyN5l Original: [2] http://goo.gl/oqGBzL * pipes-4.0: Simpler types and API Domain: haskellforall.com, Score: 95, Comments: 36 On Reddit: [3] http://goo.gl/ciVnq5 Original: [4] http://goo.gl/g9oq3i * Hackage 2 now available for beta testing -- switchover in a few weeks Domain: beta.hackage.haskell.org, Score: 91, Comments: 17 On Reddit: [5] http://goo.gl/aIhL67 Original: [6] http://goo.gl/zfprr9 * Cartesian Closed Comic #22: Cabal 1.18 Domain: ro-che.info, Score: 90, Comments: 3 On Reddit: [7] http://goo.gl/tVUUFG Original: [8] http://goo.gl/O0BR6c * Parallel and Incremental CRCs by Edward Kmett Domain: fpcomplete.com, Score: 58, Comments: 7 On Reddit: [9] http://goo.gl/YAChJl Original: [10] http://goo.gl/WnMsbY * Conquering Folds by Edward Kmett Domain: fpcomplete.com, Score: 47, Comments: 42 On Reddit: [11] http://goo.gl/reAjgu Original: [12] http://goo.gl/kHsSye * Conal Elliot: From Haskell to hardware via cartesian closed categories Domain: conal.net, Score: 47, Comments: 3 On Reddit: [13] http://goo.gl/VCwp7Y Original: [14] http://goo.gl/NO1sbs * FP Complete to release a personal edition of their online IDE Domain: fpcomplete.com, Score: 39, Comments: 38 On Reddit: [15] http://goo.gl/QOMy5Y Original: [16] http://goo.gl/XBE7zT * Quark : A Web Browser with a Formally Verified Kernel Domain: goto.ucsd.edu, Score: 36, Comments: 6 On Reddit: [17] http://goo.gl/RDZMY0 Original: [18] http://goo.gl/rgBcki * My first Haskell program - FNIStash - a utility for Torchlight 2 using threepenny for the GUI Domain: fluffynukeit.com, Score: 36, Comments: 19 On Reddit: [19] http://goo.gl/cK2N8v Original: [20] http://goo.gl/XOMTgQ * Conal Elliott: Overloading lambda Domain: conal.net, Score: 34, Comments: 4 On Reddit: [21] http://goo.gl/fQTt1P Original: [22] http://goo.gl/oPSQ3R * Cost semantics for STG in modern GHC Domain: blog.ezyang.com, Score: 31, Comments: 5 On Reddit: [23] http://goo.gl/mIQQxm Original: [24] http://goo.gl/5Sa49T * 0install - Python vs. OCaml vs. Haskell Domain: roscidus.com, Score: 31, Comments: 23 On Reddit: [25] http://goo.gl/htCf1x Original: [26] http://goo.gl/zhrVp0 * LogicGrowsOnTrees: a parallel implementation of logic programming using distributed tree exploration Domain: github.com, Score: 31, Comments: 9 On Reddit: [27] http://goo.gl/zp5lou Original: [28] http://goo.gl/5BgYh2 * RSS reader made by Haskell running on mbed platform (RAM size 64kB, using Ajhc Haskell compiler). Domain: youtube.com, Score: 30, Comments: 5 On Reddit: [29] http://goo.gl/n0Gkan Original: [30] http://goo.gl/cwL4vP * Conal Elliott: Optimizing CCCs Domain: conal.net, Score: 30, Comments: 12 On Reddit: [31] http://goo.gl/HVv8dr Original: [32] http://goo.gl/MCn0sO * Snap (and Heist) 0.13 released Domain: snapframework.com, Score: 29, Comments: 7 On Reddit: [33] http://goo.gl/zW5Sdn Original: [34] http://goo.gl/1wSLeJ * ANN: threepenny-gui-0.3 – GUI framework that uses the web browser as a display – now with FRP built-in Domain: apfelmus.nfshost.com, Score: 28, Comments: 8 On Reddit: [35] http://goo.gl/RUDrKD Original: [36] http://goo.gl/WZMeZN Top StackOverflow Questions * In Haskell, where does the range ['a'..] stop? votes: 20, answers: 2 Read on SO: [37] http://goo.gl/Oms7lr * Why were Haskell 98's standard classes made inferior to Haskell 1.3's? votes: 18, answers: 1 Read on SO: [38] http://goo.gl/WxvdL2 * 27 different Bool to Bool values in Haskell votes: 14, answers: 1 Read on SO: [39] http://goo.gl/1PcD1g * How to reconstruct Haskell expression from type votes: 10, answers: 1 Read on SO: [40] http://goo.gl/Qx06kz * Can links to anchors in haddock be labeled? votes: 8, answers: 0 Read on SO: [41] http://goo.gl/5deOMM * How to convert between ByteString and Storable Vector? votes: 7, answers: 1 Read on SO: [42] http://goo.gl/zBVVzI * Why is not GHC optimizing for constants? votes: 7, answers: 2 Read on SO: [43] http://goo.gl/sfo64S * newtype around ST causes type error votes: 7, answers: 1 Read on SO: [44] http://goo.gl/CwXaJp * GHC does not generate a binary despite no errors shown votes: 6, answers: 1 Read on SO: [45] http://goo.gl/PAv1oQ Until next time, [46]+Daniel Santa Cruz References

3 3

Mystery of an Eq instance
by damodar kulkarni 25 Sep '13

25 Sep '13

Hello, There were some recent discussions on the floating point support in Haskell and some not-so-pleasant "surprises" people encountered. There is an Eq instance defined for these types! So I tried this: *Main> sqrt (10.0) ==3.1622776601683795 True *Main> sqrt (10.0) ==3.16227766016837956 True *Main> sqrt (10.0) ==3.1622776601683795643 True *Main> sqrt (10.0) ==3.16227766016837956435443343 True It seems strange. So my doubts are: 1. I wonder how the Eq instance is defined in case of floating point types in Haskell? 2. Can the Eq instance for floating point types be considered "meaningful"? If yes, how? In general, programmers are **advised** not to base conditional branching on tests for **equality** of two floating point values. 3. Is this particular behaviour GHC specific? (I am using GHC 6.12.1) If there are references on this please share. Thanks and regards, -Damodar Kulkarni

16 33

Hackathon der Frankfurt-Haskell-User-Group
by Peter Althainz 24 Sep '13

24 Sep '13

the Frankfurt Haskell User Group announces its first Hackathon, if interested, see here: http://www.meetup.com/Frankfurt-Haskell-User-Group/events/138895112/ Peter Althainz

1 0

Strange exit status behavior from the process package
by Michael Xavier 24 Sep '13

24 Sep '13

I've run into some strangeness with the process package. When you kill some processes on the command line you correctly get a non-zero exit status. However when using the process package's terminateProcess (which sends a SIGTERM), it returns an ExitSuccess: module Main (main) where import Control.Concurrent (threadDelay) import System.Process (createProcess, proc, getProcessExitCode, terminateProcess) main :: IO () main = do (_, _, _, ph) <- createProcess $ proc "/usr/bin/sleep" ["100"] terminateProcess ph threadDelay 1000000 print =<< getProcessExitCode ph -- prints Just ExitSuccess, should be Just (ExitFailure 143) term1: sleep 100 term2: pkill sleep term1: echo $? # 143 Anyone know what might be going on? -- Michael Xavier http://www.michaelxavier.net

2 2

Creating a local Hoogle ...
by aditya siram 23 Sep '13

23 Sep '13

Hi all, I've installed Hoogle but am having issues creating the databases. I first did: `hoogle data all`, tried a search `hoogle "[a] -> a" and got: Could not find some databases: default Searching in: . ~/.cabal/share/hoogle-4.2.21/databases Either the package does not exist or has not been generated Found 4263 databases, including: abacate abcnotation abortt-monadstf abortt-mtl abortt-transformers So to create th default database I did: `hoogle combine *.hoo` and then got: Combining 4263 databases hoogle: embroidery.hoo: openFile: resource exhausted (Too many open files) Any help is appreciated. Thanks! -deech

2 1

Embedding compiled Haskell Platform in custom application
by blackbox.dev.ml 23 Sep '13

23 Sep '13

Hi! I'm writing a tool that generates haskell code, build it with cabal and launch it. I want to deliver that tool to clients, but I don't want to force them, to install system wide any specific ghc or cabal version. How can I embed compiled ghc, cabal and selected libraries (for specific platform) in installer of my application?

2 1

PSA: do not install xcode 5 if you are using ghc 7.6
by Carter Schonwald 23 Sep '13

23 Sep '13

Hey everyone, if you are actively using ghc 7.6 on your mac, for now please do not install xcode 5. It will break your ghc install, because 7.6 doesn't know how to correctly use Clang for the CPP work. (ghc head / and thus 7.8 will work fine with xcode 5, thanks to some outstanding work by Austin Seipp, 7.6 does not) if you do not need xcode 5, and you're actively using ghc 7.6, stay with xcode 4.6 for now. if you installed xcode 5 because its there, and now your ghc 7.6 is occasionally giving you strange errors involving CPP parse failures on fragments like "#-}", you should go to the apple developers website, download, and reinstall the xcode 4.6 CLI tools. if you need both xcode 5 and ghc in working order *right now, tomorrow*, either a) live on the wildside: test out using ghc head: also means you could play with ghc-ios too! b) if you need both in working order now, and stabilish, Darin Morrison has a set of mac-homebrew taps that should be you use https://github.com/darinmorrison/homebrew-haskell these taps should be regarded as more "official" and "canonical" than the formula's that brew provides (the normal brew ones recurrently have problems induced by folks who aren't haskell devs) c) wait a wee bit till 7.8 lands in all its glory, and have both the freshest of xcodes, and the newest of awesome ghcs tl;dr if you don't need xcode 5, having xcode 4.6 CLI tools installed will stand you in good stead. if you are on os x mavericks, or absolutely need xcode 5 installed, and you want a ghc thats already released, use darin's brew formulae https://github.com/darinmorrison/homebrew-haskell Darin and I plan to spend some time next month preparing an unofficial patched version of ghc 7.6 that should play nice with clang / xcode 5, though at such a time ghc 7.8 will be in RC status at the very least. cheers -Carter

4 4

A thought on the LinkedIn spam and an "upstream spam filter"
by damodar kulkarni 23 Sep '13

23 Sep '13

Hello, Sorry for dwelling on a "spammy" topic. If you are NOT interested in this then please accept my regret and let me assure you that this is NOT to add to the existing spam. If you still are unconvinced, then the only thing I can tell you is "sorry, accept my apologies for wasting your time and please stop reading further." Okay, here is what I thought of it. Yesterday I sent a mail as a response to a spam from LinkedIn to the cafe. I don't know how, but part of my mail text was missing. (I must have pressed Ctrl-C instead of Ctrl-V to paste the text from another file.) I had thought of an idea which I call "upstream spam filter". Anyway here is the text: I thought, some people here on the list, who might have links with the higher-ups at linked-in might bring the issue to their notice and would make them *register* the Haskell-Cafe list on their server so that they never send a spam to the entire list. They should install such an "upstream spam filter". This "upstream spam filter" based solution would be more effective in culling spam as compared to solutions based on requesting/heckling individual linked-in subscribers to take some action at his/her end. Note that here the individual may or may not be doing intentional spamming BUT the linkedin is *hiding* behind the subscribers' ignorance. I propose that more *influential* people on the list demand that the linked-in company should provide a way to register some emails (e.g. mailing lists) which they SHOULD spare from their spamming machines. I have already tried communicating with them but was unsuccessful. Is there any DND like service, at least, to force these big companies (like linked-in), who are happily spamming the world, behave properly?[1] Please send such protest mails to the personal email ids of the linked-in (and other such companies) top brass or other linkedin top level technical staff, if you know them. If anybody on this list is working for linkedin, then this mail is for you too. [1] http://en.wikipedia.org/wiki/Do_Not_Disturb_%28telecommunications%29 Thanks and regards, -Damodar Kulkarni On Mon, Sep 23, 2013 at 12:43 AM, MigMit <miguelimo38(a)yandex.ru> wrote: > So, instead of emailing this guy and asking him to change the address in > his LinkedIn profile (which is simple, since he did write a lot to café), > you decided to continue spamming the mailing list. > > Nice > > Отправлено с iPad > > 22 сент. 2013 г., в 21:31, damodar kulkarni <kdamodar2000(a)gmail.com> > написал(а): > > What a surprise, I didn't know the real name of "Haskell Cafe" till date, > BUT today I came to know it: it is Minh Thu V. > > linked in sucks ... > > > Thanks and regards, > -Damodar Kulkarni > > > On Sun, Sep 22, 2013 at 2:53 PM, Kyle Hanson via LinkedIn < > member(a)linkedin.com> wrote: > >> >> [image: LinkedIn] >> <http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/hom/?hs=false&tok=1F1OVFpS1PWl…> >> >> >> >> >> Hi Minh Thu, >> >> I'd like to connect with you on LinkedIn. >> >> Accept<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/XvIdBwmueHfd6vFMPXXdLaqreCbl5o…> >> >> View Profile<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454…> >> >> >> >> >> <http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454…> >> >> Kyle Hanson<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454…> >> >> Engineer at eShares, Inc. >> >> Greater Chicago Area >> >> >> >> You are receiving Invitation emails. Unsubscribe<https://www.linkedin.com/e/uc6lxc-hlw276p4-5e/XvIdBwmueHfd6vFMPXXdLaqreCbl5…>. >> >> >> This email was intended for Minh Thu Vo (Core/Server Lead Developer at >> OpenERP). Learn why we included this<http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/plh/http%3A%2F%2Flinkedin%2Ecu…>. >> © 2013, LinkedIn Corporation. 2029 Stierlin Ct. Mountain View, CA 94043, >> USA >> >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > >

2 1

GSoC Result - Communicating with Mobile devices - Push Notifications
by Marcos Pividori 23 Sep '13

23 Sep '13

I am happy to announce the result of 3 months working on the GSoC project: "Communicating with mobile devices". After reading many documentation, looking for a good abstraction, learning about mobile apps and networks connections, and really valuable recommendations from my mentor, (I really want to thank Michael Snoyman for his availability and kindness) I succeeded in developing 3 libraries to make it easy to send push notifications to mobile devices. They are available on Hackage: ** push-notify-0.1.0.0 : *This library offers a simple API for sending notifications through APNS, GCM and MPNS. [1]<http://hackage.haskell.org/package/push-notify-0.1.0.0> ** push-notify-ccs-0.1.0.0 :* This library offers an API for sending/receiving notifications through CCS (XMPP - Google Cloud Messaging). [2] <http://hackage.haskell.org/package/push-notify-ccs-0.1.0.0> ** push-notify-general-0.1.0.0 : *This library offers a general API for sending/receiving notifications, and handling the registration of devices on the server. It provides a general abstraction which can be used to communicate through different services as APNS, GCM, MPNS, hiding as much as possible, the differences between them. [3]<http://hackage.haskell.org/package/push-notify-general> Now, it is easy to send/receive information with mobile devices, so you can develop server applications which interact with them. So, to clarify this, as part of this project, I developed many test examples, including Android/WPhone and Yesod apps. I really want to thank FPComplete for giving me the possibility of hosting the Yesod app. The code is available on GitHub: [4]<https://github.com/MarcosPividori/GSoC-Communicating-with-mobile-devices> and they are running online on: [5] <http://gsoc.marcospividori.com.ar/> , so can be downloaded and tested on mobile devices. (BackAndForth Messaging and Connect4 apps) ** BackAndForth Messaging:* In this example, I show how to use the push-general library to handle the registration/reception and sending of messages. From a Yesod app [5]<http://gsoc.marcospividori.com.ar/>, you can send notifications to devices registered and receive messages from them. It is avaliable for Android and WPhone on [6]<http://gsoc.marcospividori.com.ar/apps> . ** Connect 4:* I have been thinking of an app which lets me show how useful push notifications are. The advantage of this notifications is that you can receive information from server when it is available without needing to continually poll. So, I started to think about a multiplayers game. Every time a player does something, you let the rest know about the new movement. So, I ran into the board game: "Connect 4". Both, authenticated web players and users of the android app, can play one against each other. For actualizing the website [5] <http://gsoc.marcospividori.com.ar/> , I use long polling, while for the Android app, push notifications. The Android app is available on [6]<http://gsoc.marcospividori.com.ar/apps> . Every feedback is welcome! Thanks, Marcos [1] http://hackage.haskell.org/package/push-notify-0.1.0.0 [2] http://hackage.haskell.org/package/push-notify-ccs-0.1.0.0 [3] http://hackage.haskell.org/package/push-notify-general [4] https://github.com/MarcosPividori/GSoC-Communicating-with-mobile-devices [5] http://gsoc.marcospividori.com.ar [6] http://gsoc.marcospividori.com.ar/apps

1 0

Cabal install build of scion-browser 0.2.18 fails when linking Persistent-sqlite1.21
by Stephen Taylor 23 Sep '13

23 Sep '13

Hi I'm a Haskell newbie. I just installed Haskell on Windows 7 x64 (Haskell Platform 2013.2.0.0 containing GHC 7.6.3), and have been using cabal-install to build/install from Hackage all the "helper executables" required and/or supported by EclipseFP, the Eclipse Haskell Plugin. All the helper exe's installed without any issues, except for one: scion-browser 0.2.18. All its dependencies seemed to build fine, and it built fine up until the near the end of the link phase when the link to Persistent-sqlite 1.2.1 failed. Here is the error message (path information elided): .... Loading package persistent-sqlite-1.2.1 ... ghc.exe: *Unknown PEi386 section name `.drectve'* (while processing:\persistent-sqlite-1.2.1\libHSpersistent-sqlite-1.2.1.a) ghc.exe: panic! (the 'impossible' happened) (GHC version 7.6.3 for i386-unknown-mingw32): loadArchive "persistent-sqlite-1.2.1\libHSpersistent-sqlite-1.2.1.a": failed Failed to install scion-browser-0.2.18 I understand what the message is saying, but I don't know how to go about resolving it. I have of course cleaned and retried a few times. But I get the same error. Any and all suggestions on how to resolve or work around this issue so that I can provide EclipseFP with a usable scion-browser, would be greatly appreciated. Thanks

1 0

Minh Thu, please add me to your LinkedIn network
by Kyle Hanson via LinkedIn 22 Sep '13

22 Sep '13

LinkedIn ------------ Kyle Hanson requested to add you as a connection on LinkedIn: ------------------------------------------ Minh Thu, I'd like to add you to my professional network on LinkedIn. - Kyle Accept invitation from Kyle Hanson http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/XvIdBwmueHfd6vFMPXXdLaqreCbl5o… View profile of Kyle Hanson http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/rso/60831967/_LLG/name/2272454… ------------------------------------------ You are receiving Invitation emails. This email was intended for Minh Thu Vo. Learn why this is included: http://www.linkedin.com/e/uc6lxc-hlw276p4-5e/plh/http%3A%2F%2Fhelp%2Elinked… (c) 2012, LinkedIn Corporation. 2029 Stierlin Ct, Mountain View, CA 94043, USA.

2 1

type-level integers, type-level operators, and most specific overlapping instance
by TP 22 Sep '13

22 Sep '13

Hi everybody, I encouter some problem in my code in the following simple example: two instances overlap for the multiplication sign `*`. The `OverlappingInstances` extension is of no help because it seems GHC does not look at the instance context to decide which instance is the most specific. file:///usr/share/doc/ghc-doc/html/users_guide/type-class- extensions.html#instance-overlap How to make GHC realize that in the second instance below, the instance context is not satisfied, such that the first instance has to be used? (Indeed, a Scalar is a `Tensor 'Zero`, so the strict inequality `'Zero :< n` is not satisfied in the context). -------------------------------------------- {-# LANGUAGE DataKinds #-} {-# LANGUAGE TypeFamilies #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE StandaloneDeriving #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE MultiParamTypeClasses #-} {-# LANGUAGE FunctionalDependencies #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE OverlappingInstances #-} import Prelude hiding ((*)) data Nat = Zero | Succ Nat deriving ( Show, Eq, Ord ) type family (m::Nat) :< (n::Nat) :: Bool -- Here Bool is a kind. type instance m :< 'Zero = 'False type instance 'Zero :< ('Succ n) = 'True type instance ('Succ m) :< ('Succ n) = m :< n data Tensor :: Nat -> * where Tensor :: Tensor order Mult :: Scalar -> Tensor order -> Tensor order deriving instance Show (Tensor order) type Scalar = Tensor 'Zero class Multiplication a b c | a b -> c where (*) :: a -> b -> c instance Multiplication Scalar (Tensor n) (Tensor n) where s * t = Mult s t instance (('Zero :< n) ~ 'True) => Multiplication (Tensor n) Scalar (Tensor n) where t * s = Mult s t main = do let s = Tensor :: Scalar let a = s*s print a -------------------------------------------- that yields at compilation: Overlapping instances for Multiplication Scalar Scalar (Tensor 'Zero) arising from a use of `*' Matching instances: instance [overlap ok] Multiplication Scalar (Tensor n) (Tensor n) -- Defined at test_overlapping_instance_with_typelevelinteger_test.hs:31:10 instance [overlap ok] ('Zero :< n) ~ 'True => Multiplication (Tensor n) Scalar (Tensor n) -- Defined at test_overlapping_instance_with_typelevelinteger_test.hs:34:10 In the expression: s * s In an equation for `a': a = s * s In the expression: do { let s = ...; let a = s * s; print a } Thanks in advance, TP

2 5

ANNOUNCE: New OpenGL packages
by Sven Panne 21 Sep '13

21 Sep '13

New versions of the OpenGL packages are available on Hackage: * OpenGLRaw 1.4.0.0 * GLURaw 1.4.0.0 * OpenGL 2.9.0.0 * GLUT 2.5.0.0 The mid-term goal is to make all these packages conform to the latest OpenGL 4.4 specification, and while we're not yet there, this release is nevertheless an important stepping stone towards that goal. The packages contain a few non-backwards compatible changes, something which is never nice for a public API, but it has been necessary: OpenGL has come a long way from its initial fixed function pipeline to its current form flexible form centered around shaders and buffers. Because of this, a few design decisions on the Haskell side were not a good fit anymore and simply had to change. Nevertheless, almost all changes needed in the applications and libraries using the OpenGL packages should be mechanical and straightforward. If not: hopengl(a)haskell.org is the place to get help if needed. Hopefully the new packages will make it into the next Haskell Platform release (2013.4.0.0), at least if I find out how to make it through the proposal process... ;-) Cheers, S. P.S.: Here a list of the changes for each package: ====================================================================== Changes in the OpenGLRaw package ====================================================================== * Added support for the following extensions: GL_ARB_occlusion_query2 GL_ARB_timer_query GL_ARB_draw_indirect GL_ARB_gpu_shader5 GL_ARB_tesselllation_shader GL_ARB_transform_feedback3 GL_ARB_ES2_compatibility GL_ARB_get_program_binary GL_ARB_separate_shader_objects GL_ARB_shader_atomic_counters GL_ARB_compute_shader GL_ARB_ES3_compatibility GL_ARB_framebuffer_no_attachments GL_ARB_shader_storage_buffer_object GL_ARB_query_buffer_object * Added GLfixed type from OpenGL 4.1. * Moved GLhandle type to Graphics.Rendering.OpenGL.Raw.ARB.ShaderObjects where it belongs and fixed its representation on Mac OS X. * Added new Graphics.Rendering.OpenGL.Raw.Type module which exports all GL types. Core31 and Core32 export only their respective subset now. * Correctly typed bitfield tokens as, well, GLbitfield instead of GLenum. * Consistently use ‘Ptr a’ for ‘void*’ which are not opaque. * Use ccall instead of stdcall on x86_64-windows. * Use the OpenGLES framework on iOS. ====================================================================== Changes in the GLURaw package ====================================================================== * Use ccall instead of stdcall on x86_64-windows. * Use the OpenGLES framework on iOS. ====================================================================== Changes in the OpenGL package ====================================================================== * Added sync object support. * Added full support for OpenGL 4.4 query objects, extending and changing the previous query object API a bit. * Split ObjectName class into ObjectName + GeneratableObjectName classes. Added single-name variants deleteObjectName and genObjectName, they are a very common use case. * Made BufferObject and TextureObject abstract. Now all GL objects names are abstract and have to be explicitly generated. The only exception is DisplayList, which is required to be non-abstract by the spec. * Shader is not a class anymore, but a data type with an ObjectName instance and a creation action. Added ShaderType and shaderType. * Added partial support for tessellation/geometry/compute shaders. * Program is not a GeneratableObjectName, but has a createProgram action now. Added attachShader and detachShader for incremental changes. * Deprecated shaderSource and added shaderSourceBS instead. Using ByteString is more efficient and forces the caller to think about encodings, e.g. via Data.Text.Encoding. * Added support for shader/program binaries and shader precision queries. * Revamped texture targets, adding partial support for texture buffer objects and texture arrays. * OpenGL 3.1 deprecated separate polygon draw modes, so use GL_FRONT_AND_BACK internally in polygonMode whenever possible. * Added missing Eq/Ord/Show instances for lots of data types. * Simplified TransformFeedbackVaryings API, making it a bit more similar to the one for activeAttribs and activeUniforms. * Exported ContextProfile’. * Renamed BlitFramebufferMask (to BlitBuffer) and its constructors. * Renamed BufferRangeAccessBit (to MapBufferUsage) and its constructors * Removed currentMatrix, genLists, deleteLists and isList, they have been deprecated for ages. * Full internal support for UTF-8. * Do not expose internal #hidden modules. * Lots of Haddock fixes and improvements. * Renamed IndexedTransformFeedbackBuffer to IndexedTransformFeedbackBuffer. * Fixed clip plane query. ====================================================================== Changes in the GLUT package ====================================================================== * Deprecated the misspelled ContinueExectuion constructor and added a new one correctly called ContinueExecution instead. * Use ccall instead of stdcall on x86_64-windows. * Do not expose internal #hidden modules.

2 1

using "default" declaration for overloaded numeric operations
by TP 21 Sep '13

21 Sep '13

Hi, I try to develop an embedded domain specific language in Haskell. I don't want to type "::Rational" all the time, so I try to use a default declaration for my types. This works correctly in this simple example: ------------------------------------------ default (Integer, Double) -- "default default" mag :: Float -> Float -> Float mag x y = sqrt( x^2 + y^2 ) main = do print $ mag 1 1 ------------------------------------------ Indeed we obtain sqrt(2) as a result. If we replace the default declaration by: default () , we obtain errors at compilation as expected: the type of `2` is ambiguous. Now let us consider a more complicated example: ------------------------------------------ {-# LANGUAGE FlexibleInstances #-} import Prelude hiding ((^^)) import Data.Ratio default (Integer, Rational, Double) class (Num a) => Foo a where (^^) :: Num b => b -> a -> b instance Foo Rational where (^^) x r = x ^ n where n = 2*numerator r -- dummy calculation instance Foo Integer where (^^) x n = x ^ n mag :: Float -> Float -> Float mag x y = sqrt( x ^^ 2 + y ^^ 2 ) main = do print $ mag 1 1 ------------------------------------------ I would expect it to work correctly, but we obtain errors concerning the ambiguous type of `2`. Why? How to make my default declaration work? And if I want to give the priority to `Rational` instead of `Integer`? Indeed, this should be possible because we don't get any error below. $ ghci > import Data.Ratio > 2::Rational 2 % 1 Thanks in advance, TP

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Demarcating monad transformers.
by Nickolay Kudasov 21 Sep '13

21 Sep '13

Hi Café, Below I describe what I call «demarcating monad transformer». It works great for my purposes, though the construction feels a bit awkward. Perhaps, this is just an instance of a general case. For details and example, see [1] (single module package). Recently I got a challenge of manipulating transformed monadic values. In my case the value was of type t (Free f) a (or MonadFree m => t m a). The challange itself was to provide a function: transform :: (Functor f, MonadTrans t) => (forall b. f b -> t (Free f) b) -> t (Free f) a -> t (Free f) a The type t (Free f) a for my purposes can be read as «a program with low-level API specified with functor f and extra features specified with monad transformer t». transform takes a “basic transformation” phi and an abstract program p and applies phi whenever p “executes” command of free functor f. It turns out that this function is impossible (try StateT). The point is that you can't “get inside” of transformed monadic value. So I came up with idea of «demarcating» monad transformer. By «demarcating» I mean separating pure monadic computations (lifted m a) from transformed ones (t m a). Such separation can be made explicit with the help of free monads: data DemarcateF t m next = forall b. DemarcateMonad (m b) (b -> next) -- "pure" monadic computation | forall b. DemarcateTrans (t m b) (b -> next) -- transformed monadic computation instance Functor (Demarcate t m) where ... -- getting monad for freenewtype Demarcate t m a = Demarcate { unDemarcate :: Free (DemarcateF t m) a } instance Monad (Demarcate t m) where ...instance MonadTrans (Demarcate t) where ... With that I can define transform functions: -- transform arbitrary monadic computationtransformDemarcateM :: (forall b. m b -> Demarcate t m b) -> Demarcate t m a -> Demarcate t m a -- transform free monadic actionstransformDemarcateFree :: (forall b. f b -> Demarcate t (Free f) b) -> Demarcate t (Free f) a -> Demarcate t (Free f) atransformDemarcateFree phi = transformDemarcateM (iterM phi) The complete code is available at [1]. Check out examples/simple.hs for a use case. Now the questions are: - has anyone else encountered such a challenge? - is this solution an instance of a more general pattern? - is it sensible to use Demarcate t m a when m is not a free monad? - how Demarcate may affect the performance? Thanks in advance, Nick [1] <https://github.com/fizruk/demarcate>https://github.com/fizruk/demarcate

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Which builder to choose?
by Alejandro Serrano Mena 20 Sep '13

20 Sep '13

Hi, I'm looking at the packages blaze-builder and bytestring, and both provide builders for ByteString. Which one should I use? In which situations is one more convenient than the other? Thanks for the help.

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Fwd: Functional Programming in Bioinformatics, Birds-of-a-Feather Session at CUFP
by Ashish Agarwal 19 Sep '13

19 Sep '13

Functional Programming in Bioinformatics Birds-of-a-Feather Session at CUFP 2013 September 23, 2013 at 6:00 PM Boston, MA United States Bioinformatics is a discipline applying computational methods to biological problems. Due to advances in experimental techniques, especially in next-generation DNA sequencing, the amount of data being generated by biologists is exponentially increasing. The resulting data deluge promises to accelerate fundamental advances in human health, agriculture, and basic research. However, progress is hindered due to the lack of software tools for managing, analyzing, visualizing, and sharing such data. The goal of this meeting is to bring together researchers and practitioners of functional programming, logic, type theory, and related fields who are interested in applying their skills to biology and medicine. We also welcome biologists who are curious about state-of-the-art software engineering techniques. The meeting will be casual with no presentations. Our goal is simply to meet and discuss our interests, and propose future events and collaborations. We will meet at Connolly’s Publik House within the conference venue, the Hilton Boston Logan Airport Hotel, on Monday September 23rd at 6:00 PM. Everyone is welcome to attend this meeting regardless of whether you registered for any ICFP or CUFP events. RSVP is not required, but to help with planning, please email “agarwal1975 at gmail.com” if you know you will attend. Please also join the Well-Formed-Bio mailing list [1], which we welcome everyone to use for discussions around the topic of formal software methods applied to biology. [1] https://groups.google.com/forum/#!forum/well-formed-bio [2] http://cufp.org/conference/sessions/2013/birds-feather-functional-programmi… Organizers: Ashish Agarwal, Jeff Hammerbacher

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