- Haskell-Cafe - Haskell.org

Simply and easy graphical toolkit?
by Christopher Howard 24 Sep '15

24 Sep '15

Hi. What would be the simplest and easiest Haskell graphical toolkit to use? I remember a few years ago I tried Gloss and was really happy with it, but I also wanted to be able to have a few buttons and text fields on the screen for user input, without having to build them from scratch. -- http://justonemoremathproblem.com/

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ANN: The Herbie GHC Plugin
by Mike Izbicki 24 Sep '15

24 Sep '15

80% of packages in stackage that contain floating point expressions have numerically unstable expressions. The Herbie GHC plugin automatically makes these expressions numerically stable. You can find the project on github at: https://github.com/mikeizbicki/HerbiePlugin

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ANN: CfN for new Haskell Prime language committee
by Herbert Valerio Riedel 23 Sep '15

23 Sep '15

Dear Haskell Community, In short, it's time to assemble a new Haskell Prime language committee. Please refer to the CfN at https://mail.haskell.org/pipermail/haskell-prime/2015-September/003936.html for more details. Cheers, hvr -- PGP fingerprint: 427C B69A AC9D 00F2 A43C AF1C BA3C BA3F FE22 B574

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ANN: FunGEn-1.0 - easy-to-install cross-platform game engine
by Simon Michael 21 Sep '15

21 Sep '15

I'm pleased to announce the release of FunGEn 1.0 ! What is it ? FunGEn (Functional Game Engine) is the oldest game engine in Haskell. It was created by Andre Furtado in 2002, has never been used since, and yet it is arguably still the easiest and most practical way to make a video game using Haskell. It is BSD-licensed, installs easily on unix, mac and windows, does not use FRP, and comes with two playable example games. What does it do ? Here's Andre's original feature list: - Initialization, updating, removing, rendering and grouping routines for game objects; - Definition of a game background (or map), including texture-based maps and tile maps; - Reading and intepretation of the player's keyboard input; - Collision detection; - Time-based functions and pre-defined game actions; - Loading and displaying of 24-bit bitmap files; - Some debugging and game performance evaluation facilities; - Sound support (actually for windows platforms only... :-[ ) What's new in 1.0 ? - supports GHC 7.10 - supports stack - the repo (and project) has moved to the haskell-game organization on Github How to install $ cabal update $ cabal install FunGEn # ensure ~/.cabal/bin or windows equiv. is in your PATH or $ git clone https://github.com/haskell-game/fungen $ cd fungen $ stack install How to run the examples $ fungen-hello $ fungen-pong $ fungen-worms More info http://hackage.haskell.org/package/FunGEn https://github.com/haskell-game/fungen http://joyful.com/fungen - old home page Why ? I think FunGEn still has some value, for building games and also as an example of how to structure games in haskell. I don't have time to do much with it, so I've moved it to the haskell-game organization, where all org members now have push access. I'd like it to be as open as possible to contributors, and am seeking a new or co- maintainer. Best, -Simon (sm on #haskell-game)

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GSoC Retrospective
by Dominic Steinitz 20 Sep '15

20 Sep '15

In past years, Gwern did an outstanding job of summarising the GSoC proposals and how well they had done: http://www.gwern.net/Haskell%20Summer%20of%20Code <http://www.gwern.net/Haskell%20Summer%20of%20Code> Here are the proposals for this year. Perhaps students or their mentors could comment on how successful their projects have been? I realise this is a very poor substitute for Gwen’s analyses but it would better than nothing. A Strict language pragma for GHC - Adam Sandberg Eriksson <https://github.com/adamse> STM Data Structures Implementation <https://gist.github.com/Alllex/439480b7e80303f19ddc> - Alex Semin Implementation of Layered Gramamar of Graphics <https://gist.github.com/AjayRamanathan/c84a4641836700a2547b> - chinu <https://github.com/AjayRamanathan/Plot> Implementing Version Comparison for Cabal Packages - Craig Roche <https://github.com/cdxr> Improving Hackage Discoverability <http://dzackgarza.com/mockup/main.html> - D. Zack Garza <https://github.com/dzackgarza> Darcsden improvements <http://darcs.net/GSoC/2015-Darcsden> - Daniil Frumin <https://github.com/co-dan> Pursuit enhancements <https://gist.github.com/hdgarrood/0a389937149453c69e03> - Harry Garrood <https://github.com/hdgarrood> Improvements For HBLAS And Adding LAPACK Bindings. - JuejiYang A standalone functional parser for CommonMark <https://gist.github.com/Jubobs/7a9298eeaf02bcefbc35> - Julien Cretel <https://github.com/Jubobs> Refactor program with HLint suggestions <http://mpickering.github.io/gsoc2015.html> - Matthew Pickering <https://github.com/mpickering> Replication back-end for acid-state - Max Voit Native Haskell Type Encoding for LiquidHaskell <https://gist.github.com/spinda/b261167303515cc8a1d9> - Michael Smith <https://github.com/spinda> Exhaustiveness Checker for PureScript - Nicolas Del Piano <https://github.com/nicodelpiano> Fast splittable pseudorandom number generator for System.Random <https://gist.github.com/nkartashov/e46fd146b1df2d79aaf3> - Nikita Kartashov <https://github.com/nkartashov> Interactive widgets in IHaskell <https://github.com/sumitsahrawat/gsoc/blob/master/2015/ihaskell.pdf> - Sumit Sahrawat <https://github.com/sumitsahrawat> Improvements to yesod-devel - urbanslug <https://github.com/urbanslug> Implement nix-like package management features in cabal <https://gist.github.com/fugyk/37510958b52589737274> - Vishal Agrawal <https://github.com/fugyk> Haddock improvements - Łukasz Hanuszczak <https://github.com/mrhania> Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

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MonadPlus and Alternative folds
by David Feuer 19 Sep '15

19 Sep '15

It kind of seems like there should be fold-like things to match some and many. foldrAlt :: Alternative f => (a -> b -> b) -> b -> f a -> f b foldrAlt c n m = foldr1Alt c n m <|> pure n foldr1Alt :: Alternative f => (a -> b -> b) -> b -> f a -> f b foldr1Alt c n m = c <$> m <*> foldrAlt c n m foldlMP' :: MonadPlus f => (b -> a -> b) -> b -> f a -> f b foldlMP' f b m = foldl1MP' f b m <|> pure b foldl1MP' :: MonadPlus f => (b -> a -> b) -> b -> f a -> f b foldl1MP' f b m = m >>= \r -> let !b' = f b r in foldlMP' f b' m --These look a bit iffy foldlAlt :: Alternative f => (b -> a -> b) -> b -> f a -> f b foldlAlt f b m = ($ b) <$> foldrAlt (\x r acc -> r (f acc x)) id m foldl1Alt :: Alternative f => (b -> a -> b) -> b -> f a -> f b foldl1Alt f b m = ($ b) <$> foldr1Alt (\x r acc -> r (f acc x)) id m Do these or similar exist somewhere? If not, should they exist somewhere? I'm particularly interested in whether either of these will be fast, or will admit a fast implementation, for attoparsec parsers. Thanks, David Feuer

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Re: [Haskell-cafe] MonadPlus and Alternative folds
by Olaf Klinke 19 Sep '15

19 Sep '15

Is there an instance of Alternative where some and many are not bottom? The usual example monads, [] and Maybe, don't serve as a source of intuition. In general I agree with David: If f is a functor such that every type (f a) is a monoid, then there should be folds. The usual question here is: Your functions have types more general than the known foldr and foldl. Do your functions specialize to the known ones? It seems not. For example, foldrAlt (+) 0 [1,2,3] diverges, and so does foldlMP' (+) 0 [1,2,3]. I have doubts that knowing how to append two lists gives you access to the recursive structure of a list. Note that mplus is a _constructor_ of lists, while recursion is built on _destructors_. The same seems to apply to all other functions provided by Applicative, Alternative and MonadPlus. The foldr of Data.Foldable, by contrast, accepts a foldable structure and produces something which is not a foldable structure. Hence it must have access to the internals of that foldable structure. Olaf

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Why Haskell is beautiful to the novice
by Olaf Klinke 19 Sep '15

19 Sep '15

Dear cafe, please correct me if questions like this should not go via this mailing list. Presumably everyone on this list agrees that Haskell stands out as a beautiful and pleasant language to have. The recent nitpicking and real-world problems like cabal hell don't change that. However, statements supporting Haskell's beauty usually involve: "In Haskell it is so much clearer/easier/faster to ... than in another language." That is, the beauty of Haskell presents itself to those who can compare it to other imperative or not strongly typed languages that one learned before Haskell. My question is, for what reason should anyone not acquainted with any programming language find Haskell beautiful? Maybe it does not look beautiful at all to the novice. The novice can not draw on the comparison, unless he takes the effort to learn more than one language in parallel. The novice likely also does not have the mathematical background to see the beautiful correspondence between the language and its semantics. (My reason to love FP is because it is executable domain theory.) One might argue that it is not the language itself that is beautiful, but rather the concepts (data structures, algorithms, recursion) and Haskell does a great job to preserve their beauty into the implementation. Do you agree? Disclaimer: I am about to start teaching a first course in computer science in secondary school. I can teach whatever I want, since this is the first CS course the school ever had. I want to teach beautiful things. I love functional programming. I need not start teaching programming right away. But I am reluctant to expose the pupils to something whose beauty escapes them completely. -- Olaf

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persistent sqlite: getting record by ID
by miro 19 Sep '15

19 Sep '15

Please, can you help me with following? I’m trying to get a record from sqlite by id. I have found following peace of code,…but I’m missing the place that where can I specify the table I’m actually querying (like PersonId). get $ Key $ (PersistInt64 $ fromIntegral id) Cheers, Miro

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Looking for better than Dragon Book
by Michael Litchard 18 Sep '15

18 Sep '15

I've got the Tiger Book, ML version, which I will use to help me implement Tiger in Haskell. Below is a class curriculum I've found. But besides the Tiger Book, it uses the Dragon Book. I know there are more modern books out there. Looking for suggestions as what might be a good fit. http://cs.nyu.edu/courses/fall13/CSCI-GA.2130-001/

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