April 2017 - Haskell-Cafe

Cross-compiling GHC
by Jan von Löwenstein 18 Apr '17

18 Apr '17

Hi, I would like to have an integer-simple GHC for Mac and Linux. As there is no official download for that I should probably build it myself. My CI server is running Linux containers though. When https://ghc.haskell.org/trac/ghc/wiki/Building/CrossCompiling says "build must equal host", does that mean I cannot produce a mac ghc with Linux ci server? How do others produce ghc for mac or Windows? Best Jan

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slow type level function
by Baojun Wang 18 Apr '17

18 Apr '17

Hello cafe, I tried to play with some type level natural numbers, and it seems type level function is quite slow, for instance: (full source) https://gist.github.com/wangbj/5939aa7a30c3d756d98f5b5775e162a6 data Z data S n class KnownNat n where natSing :: n -> Integer instance KnownNat Z where natSing _ = 0 instance KnownNat n => KnownNat (S n) where natSing _ = 1 + natSing (undefined :: n) natVal :: KnownNat n => n -> Integer natVal = natSing natSing doesn't seems to know how to optimize when KnownNat is very big (i.e: 10000), I tried Peano Add/Mul, and they are very slow to be really useful. Is there any ways to improve this? How fully dependent typed language such as Adga/Idris handle this, do they have the same performance issue? Thanks baojun

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Re: [Haskell-cafe] Wow Monads!
by David McClain 18 Apr '17

18 Apr '17

Your’e welcome… > On Apr 18, 2017, at 10:20, Bryan Richter <b(a)chreekat.net> wrote: > > On Tue, Apr 18, 2017 at 09:57:10AM -0700, David McClain wrote: >> <...> > > These posts of yours have been incredibly interesting to me, and I just > wanted to thank you for sharing them! I think my point about ecosystem programming is really about the importance of immediate feedback when crafting software. You need a powerful language so that you don’t get torpedoed with your fresh ideas with lots of mandatory scaffolding. In C-like languages the goal becomes one of writing a correct line of code. The strongly typed languages, of the FPL variety, don’t force that upon you. But you do get sidetracked by the challenge of getting that last bit of code to type check successfully. And if you aren’t already in an ecosystem with the language, even more distracted by the demands of the edit / compile cycle. Any distractions from your idea means that, if you happened to have chosen the wrong approach, you aren’t thinking properly about that aspect because the distractions have set up a nearer term goal for you to reach. We become like hamsters on a wheel, and we feel good after doing battle successfully. But the problem is, after all that, did it work the way you hoped? And without immediate feedback, even if you have some distractions that you must put up with, you are using an extended tape measure to flip the light switch on the opposite wall. I think Haskell does offer some ecosystems. I have one that I installed on my Mac a couple months ago called “Haskell for Mac” by Chakravarty. It seems a pretty nifty little environment, but I have only been in there for about an hour or two. Part of my own push for polygot creds. Another one that looks possibly interesting is Shen, formerly Qi. I did a fair amount with the old Qi language, even adding / correcting the compiler system to fit my own needs. Mastering the logic system is another challenge ahead of me. I was impressed at the implementation, and the equational reasoning, which I first saw back in the 1990’s with the publication of the SML Language. But right off the bat, Haskell will present the bigger challenge to me. There is a huge scaffold of type class hierarchy that comes in the base environment. Reminds me a bit of trying to learn the old MSVC system from yore… - DM

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containers: Efficiently concatenating nested maps (or should I look at another data structure)
by Oliver Charles 18 Apr '17

18 Apr '17

Hi all, First, a little context. I'm currently working on [1] a little OpenGL project - a Quake 3 map viewer in Haskell. For the most part, things are working out great, but the way I construct the scene is costing me a lot of alloction, and I wonder if I can do better. The OpenGL system is essentially a giant state machine. Whenever you issue a draw call ("draw these triangles"), OpenGL will do different things depending on what the state is. For example, if you have a texture bound, then the triangle will be textured, and if you have blending enabled, then the triangle might be blended into whatever was drawn previously. While this can be tricky to manage, Haskell does a good job of giving us tools to model state. The real spanner is that state transitions are not free. In the above example, the state transitions associated with binding a texture or enabling blending both cost time - and this time is variable depending on the state change. In this case, setting the currently bound texture is a very expensive operation, whereas setting the blending mode is less costly. For this reason, it's common in graphics programming to want to sort draw calls to minimise state changes. For example, we might draw all triangles with texture 1, then all triangles with texture 2 - rather than interleaving those draw calls. To model this in Haskell, I'm using a tree-like structure to group and express each state change [2]. To give you an example of what this looks like, I have: class RenderNode a m where draw :: a -> m () instance RenderNode (IO ()) IO where draw = id newtype BindTexture a = BindTexture (MonoidalIntMap a) [3] deriving (Functor, Monoid) instance (MonadIO m, RenderNode a m) => RenderNode (BindTexture a) m where draw (BindTexture t) = IM.foldrWithKey (\texture0 m next -> do glActiveTexture GL_TEXTURE0 glBindTexture GL_TEXTURE_2D (fromIntegral texture0) draw m next) (return ()) (getMonoidalIntMap t) newtype BlendMode a = BlendMode (MonoidalMap (GLuint, GLuint) a) [3] deriving (Functor, Monoid) blendMode :: (GLuint, GLuint) -> a -> BlendMode a blendMode srcDst = BlendMode . MonoidalMap . Map.singleton srcDst instance (MonadIO m, RenderNode a m) => RenderNode (BlendMode a) m where draw (BlendMode m) = Map.foldrWithKey (\(srcBlend, destBlend) child next -> do glBlendFunc srcBlend destBlend draw child next) (return ()) (getMonoidalMap m) I can then stack these nodes together to form a "render graph": newtype RenderGraph = RenderGraph (BindTexture (BlendMode (IO ()))) deriving (Monoid) The IO action at the leaf corresponds to a draw call to draw some triangles. Now that I've explained the basics of my rendering plan, I just need to tell you a little bit about Quake 3 maps. A Quake 3 map is essentially a big soup of "faces", where each face is a collection of triangles (that can be drawn in one call) and a set of associated state. Furthermore, each face is assigned a "cluster" (an Int), and we have a function that given a cluster gives us back a list of other clusters that we can "see" - this is visibility determination, or occlusion culling. I am hence modelling the map as an IntMap RenderGraph - each cluster maps to a RenderGraph of how to draw all the faces in that cluster, organised to minimise draw calls. Then, given some sort of visibility check, when I render I filter this IntMap to only the clusters that can be seen, and combine all the render graphs: IntMap.foldlWithKey' (\scene clusterNumber clusterFaces -> scene <> clusterFaces) mempty clusters In reality, this results in combining a few hundred-thousad very deeply nested structures, and naturally that's resulting in a fair bit of allocation pressure. I need to do this almost every frame, because as the camera moves, we might be able to see different clusters, so I don't think there's really much that I can cache. My actual final RenderGraph is Sort |> Cull |> MultiplePasses |> BindTexture |> SetUniform Bool |> SetDynamicUniform (M33 Float) |> AlphaFunc |> BlendMode |> DepthFunc where (|>) is Functor composition, and each of those functors is either a Map or IntMap. It seems to deteriorate to pairwise `mappend`, as you can see from the definition of mappend for MonoidalMap or MonoidalIntMap in [3]. Can anyone think of any obvious ways to rewrite this to have less allocation pressure? I'm of course open to other ways to batch operations, but there is something I find quite beautiful about shoving everything into Maps and mappending them. In the C world, the approach is usually to combine all the states into a single bitmask, and then sort that. That same approach might be possible here, but I'd like to keep the pick-and-choose compositional nature that I've got above. Thanks for reading this far, I hope my post has made sense. If you need clarification on anything, the source is below, and don't hesitate to ask me any questions! -- ocharles [1]: http://github.com/ocharles/hs-quake-3 [2]: https://github.com/ocharles/hs-quake-3/blob/master/RenderGraph.hs [3]: newtype MonoidalMap k a = MonoidalMap { getMonoidalMap :: Map k a } instance Functor (MonoidalMap k) where fmap f (MonoidalMap a) = MonoidalMap (fmap f a) instance (Monoid a, Ord k) => Monoid (MonoidalMap k a) where mempty = MonoidalMap Map.empty mappend (MonoidalMap a) (MonoidalMap b) = MonoidalMap (Map.unionWith mappend a b) mconcat = coerce . Map.unionsWith mappend . (coerce :: [MonoidalMap k a] -> [Map k a]) newtype MonoidalIntMap a = MonoidalIntMap { getMonoidalIntMap :: IntMap a } deriving (Functor) instance Monoid a => Monoid (MonoidalIntMap a) where mempty = MonoidalIntMap IM.empty mappend (MonoidalIntMap a) (MonoidalIntMap b) = MonoidalIntMap (IM.unionWith mappend a b) mconcat = coerce . IM.unionsWith mappend . (coerce :: [MonoidalIntMap a] -> [IntMap a])

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VSTTE 2017 - Second Call for Papers
by Andrei Paskevich 18 Apr '17

18 Apr '17

9th Working Conference on Verified Software: Theories, Tools, and Experiments (VSTTE) https://vstte17.lri.fr July 22-23, 2017, Heidelberg, Germany Co-located with the 29th International Conference on Computer-Aided Verification, CAV 2017 Important Dates * Abstract submission: Mon, Apr 24, 2017 * Full paper submission: Mon, May 1, 2017 * Notification: Mon, Jun 5, 2017 * VSTTE: Sat-Sun, Jul 22-23, 2017 * Camera-ready: Mon, Aug 21, 2017 Overview The goal of the VSTTE conference series is to advance the state of the art in the science and technology of software verification, through the interaction of theory development, tool evolution, and experimental validation. We welcome submissions describing significant advances in the production of verified software, i.e., software that has been proved to meet its functional specifications. Submissions of theoretical, practical, and experimental contributions are equally encouraged, including those that focus on specific problems or problem domains. We are especially interested in submissions describing large-scale verification efforts that involve collaboration, theory unification, tool integration, and formalized domain knowledge. We also welcome papers describing novel experiments and case studies evaluating verification techniques and technologies. Topics of interest for VSTTE include education, requirements modeling, specification languages, specification/verification/certification case studies, formal calculi, software design methods, automatic code generation, refinement methodologies, compositional analysis, verification tools (e.g., static analysis, dynamic analysis, model checking, theorem proving, satisfiability), tool integration, benchmarks, challenge problems, and integrated verification environments. Paper Submissions We accept both long (limited to 16 pages) and short (limited to 10 pages) paper submissions. Short submissions also cover Verification Pearls describing an elegant proof or proof technique. Submitted research papers and system descriptions must be original and not submitted for publication elsewhere. Each submission will be evaluated by at least three members of the Program Committee. We expect that one author of every accepted paper will present their work at the conference. Paper submissions must be written in English using the LNCS LaTeX format (http://www.springer.com/gp/computer-science/lncs/conference-proceedings-gui…) and must include a cogent and self-contained description of the ideas, methods, results, and comparison to existing work. Papers will be submitted via EasyChair at the VSTTE 2017 conference page (https://www.easychair.org/conferences/?conf=vstte2017) The post-conference proceedings of VSTTE 2017 will be published in the LNCS series. Authors of accepted papers will be requested to sign the copyright transfer form. A selection of best papers will be invited for publication in the Journal of Automated Reasoning. Invited Speakers * Christoph Weidenbach (Max Planck Institute for Informatics, Germany) * Santiago Zanella-Beguelin (Microsoft Research, UK) Program Committee * June Andronick (University of New South Wales, Australia) * Christel Baier (TU Dresden, Germany) * Sandrine Blazy (Université de Rennes 1, France) * Arthur Charguéraud (Inria, France) * Ernie Cohen (Amazon Web Services, USA) * Rayna Dimitrova (MPI-SWS, Germany) * Carlo A. Furia (Chalmers University of Technology, Sweden) * Arie Gurfinkel (University of Waterloo, Canada) * Hossein Hojjat (Rochester Institute of Technology, USA) * Marieke Huisman (University of Twente, Netherlands) * Bart Jacobs (KU Leuven, Belgium) * Rajeev Joshi (NASA Jet Propulsion Laboratory, USA) * Zachary Kincaid (Princeton University, USA) * Akash Lal (Microsoft Research, India) * Shuvendu Lahiri (Microsoft Research, USA) * Francesco Logozzo (Facebook, USA) * Peter Müller (ETH Zürich, Switzerland) * Jorge A. Navas (SRI International, USA) * Scott Owens (University of Kent, UK) * Andrei Paskevich (Université Paris-Sud, France), co-chair * Gerhard Schellhorn (Universität Augsburg, Germany) * Peter Schrammel (University of Sussex, UK) * Natarajan Shankar (SRI International, USA) * Mihaela Sighireanu (Université Paris-Diderot, France) * Julien Signoles (CEA LIST, France) * Michael Tautschnig (Queen Mary University of London, UK) * Tachio Terauchi (JAIST, Japan) * Oksana Tkachuk (NASA Ames Research Center, USA) * Mattias Ulbrich (Karlsruhe Institute of Technology, Germany) * Thomas Wies (New York University, USA), co-chair

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Req. for co-maintaining hs-libhdf5 and bindings-hdf5
by Marco Zocca 18 Apr '17

18 Apr '17

Dear all, I would like to help taking care of two libraries for HDF5. The author, James Cook (mokus0 on GitHub, CC'd here), didn't reply to a private email I sent about this on April 12. I hope he's doing well, by the way. HDF5 is a popular format for scientific datasets, and it would be a pity to see the Haskell bindings bitrot. I have previous experience building Haskell C bindings with HSC, c2hs and inline-c, and as co-maintainer I would, as first steps, add memory brackets and user-facing `exceptions`, enable continuous integration (Travis) and "stack-ify" the libraries. Hoping to hear soon from James and/or the Hackage trustees; All the best, Marco (ocramz)

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Call for participation: PLDI 2017 and co-located events
by Tobias Grosser 17 Apr '17

17 Apr '17

Call for participation: PLDI 2017 and co-located events PLDI is the premier forum in the field of programming languages and programming systems research, covering the areas of design, implementation, theory, applications, and performance. The co-located conferences take place in Barcelona, June 18-23, 2017. This year, PLDI is co-located with ECOOP, LCTES, DEBS, ISMM, Curry On and others. The conferences will take place at the Universitat Polytècnica de Catalunya in Barcelona, Spain. http://conf.researchr.org/home/pldi-2017 Registration is now open, please visit: https://regmaster4.com/2017conf/BARC17/register.php to register. The early registration rate ends on May 26th. The tentative program is available at: http://pldi17.sigplan.org/program/program-pldi-2017 PLDI will also hold an ACM Student Research Competition: http://pldi17.sigplan.org/track/pldi-2017-student-research-competition Co-located events: + ECOOP: European Conference on Object-Oriented Programming + DEBS: annual conference on Distributed Event-Based Systems + Curry On: conference on programming languages and emerging challenges in industry. + ISMM: International Symposium on Memory Management + LCTES: Languages, Compilers, and Tools for Embedded Systems Co-located workshops include: + ARRAY: Workshop on Libraries, Languages and Compilers for Array Programming + DSW: Deep Specifications in the Wild + FMS: Formal Methods for Security + IC: Workshop on Incremental Computing + MAPL: Machine Learning and Programming Languages + PLMW: Programming Languages Mentoring Workshop + SOAP: International Workshop on the State Of the Art in Java Program Analysis + WCIRE: Workshop for Compiler Infrastructure for Research and Education Additionally, there will be eight co-located tutorials: + Bug detection in JavaScript web apps using the SAFE framework + Building your own modular static analyzer with Facebook Infer + Engineering Static Analyzers with Soufflé + Graal: High Performance Compilation for Managed Languages + P4: Programming the Network Data Plane + Polyhedral Compilation + Refinement Types for Program Verification and Synthesis + Scala, LMS and Delite for High-Performance DSLs and Program Generators + WALA Hack-A-Thon + Writing Verified Programs in CakeML See the web site for a schedule and further details and links. For further updates, follow PLDI on the social media: Facebook: https://www.facebook.com/PLDIConf Twitter: https://twitter.com/PLDI Albert Cohen, PLDI 2017 General Chair Tobias Grosser, PLDI 2017 Publicity Chair

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Re: [Haskell-cafe] Wow Monads!
by David McClain 17 Apr '17

17 Apr '17

That was absolutely excellent !! Great video presentation by Douglas Crockford. It took me about 2 hours to slowly advance through it, stopping along the way to translate his JS into Lisp to try out the Monads. This is by far the clearest explanation of Monads that I have seen, from among at least 2 dozen different videos and blogs. Even clearer than that Wadler paper. I highly recommend viewing this presentation. As for the rest of them, I hearken to the words of another great scientist who once stated that: “If you can’t explain a problem to your grandmother so that she understands it, then you don’t really understand the problem yourself…" - DM >> On Apr 16, 2017, at 15:43, MarLinn <monkleyon(a)gmail.com> wrote: >> >> On 2017-04-16 03:13, John Wiegley wrote: >>> MD> Anyone else have Lisp experience using Monads? Did it offer some major enhancements for you? >>> >>> In Lisp, I don't think the abstraction buys you much, because all the functionality you need (state, exceptions, runtime, etc) are always available to all expressions. They become an excellent way of representing "extensible composition" in a pure language that otherwise could not allow those things, but I don't see that you need it for an untyped language like Lisp. >> >> May I present to you the lecture "Monads and Gonads" by Douglas Crockford (https://www.youtube.com/watch?v=b0EF0VTs9Dc) He shows that monads can make even a language like JavaScript useful (not his words). And the talk is one of the better monad tutorials out there to boot, not least because it's different from all the others. >> >> My own conclusion from it is that I would maybe even turn your argument around and claim that especially a language that has as few tools to keep programs sensible as JS can benefit greatly from the structure a monad provides. The benefits will be different for Lisp, but I imagine there might be some nice use cases as well. After all, structures are a great tool even if you're not forced to use them. ;) >> >> On another note: the more I work with monads and their brethren, the more I find myself thinking in terms of (a -> f b) functions instead of things like bind. Not only is it closer to the mathematical basis, but there's also the close relationship to lenses. I mention this because my feeling is that this type of function is a more usable puzzle piece in languages with limited syntax support. Especially if you also implement functors. But that's just unsubstantiated gut feeling. >> >> Cheers, >> MarLinn >> >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe >> Only members subscribed via the mailman list are allowed to post. >

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Ensuring that blank-state has been handled in UIs?
by Saurabh Nanda 16 Apr '17

16 Apr '17

Hi Everyone, In most user-interfaces we need special-treatment for blank states (zero-item state). For example: * In case there are no customers, don't show an empty table, instead show the message "You seem to have no customers, why not start by creating one..." * In case there are no bookings, don't show an empty table, instead show the message, "No bookings here. Want to create one?" * In case there are no search results, don't show an empty table, instead show the message, "No items found. Undo your last filter?" In some cases, the one-item case also needs special treatment, but I'm unable to come with relatable examples at the moment. A lot of times the dev simply forgets about the blank state, and it is caught during QA, which results in a quick-fix on the following lines: if length item > 0 then displayTable else showBlankState if Data.Map.Strict.size map > 0 then displayTable else showBlankState if Data.Set.Ordered.size set > 0 then displayTable else showBlankState Is there a way to prevent this bug from the get-go? Can we use the type-system (or anything else) to enforce the dev to at least _think_ about the blank state? Obviously, the type system can't help us with _what_ needs to be done with the blank state, but at least it can _remind_ the dev at compile-time about handling blank states. -- Saurabh.

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ANN: projects available for adoption
by Simon Michael 16 Apr '17

16 Apr '17

Hi all, to increase focus on other things, I am offering the following projects for adoption. Are you interested in one of these ? Would you like to pick it up and make it shine ? Ideally you are a regular user of the project yourself, and will be a more active maintainer than I have been. Or, you might like to try being co-maintainer or release manager for a time. Let's talk! http://joyful.com/shelltestrunner - compares command-line programs or shell commands with expected output. http://hackage.haskell.org/package/quickbench - produces quick, readable comparative benchmarks of program invocations. http://hackage.haskell.org/package/rss2irc - an IRC bot that announces any RSS/Atom feed to IRC. Formerly used for hackagebot in #haskell. http://joyful.com/fungen - the oldest and easiest way to build cross platform, easy to install 2D games in haskell. Also: http://planet.darcs.net <http://planet.darcs.net/> - Darcs-related feed aggregator (Planet Venus) http://planet.squeak.org <http://planet.squeak.org/> - Squeak Smalltalk-related feed aggregators (Planet Venus) http://hub.darcs.net/simon/darcsum <http://hub.darcs.net/simon/darcsum> - emacs UI for darcs (think mini-magit) (elisp) http://zwiki.org <http://zwiki.org/> - a powerful wiki engine built on the Zope 2 platform. (Long shot, just putting it out there.) (python) Best! -Simon

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