July 2016 - Haskell-Cafe

Is there any way in GHC plugin to refer exposed but defined in a hidden module?
by Hiromi ISHII 25 Jul '16

25 Jul '16

Hi Cafe, I'm currently writing a simple GHC Typechecker plugin to augment typelevel naturals with a presburger arithmetic solver [^1]. I want to use type-class constraints to give premisses to the solver, for example, `Empty a` constraint means "a is false (empty type)". So I have to get TyCon information in TcPluginM monad and I wrote as follows: ```haskell do md <- lookupModule (mkModuleName "Proof.Propositional.Empty") (fsLit "equational-reasoning") classTyCon <$> (tcLookupClass =<< lookupOrig md (mkTcOcc "Empty")) ``` But this code doesn't work as expected. For example, the code ```haskell {-# LANGUAGE DataKinds, TypeOperators, GADTs, TypeFamilies, ExplicitForAll, FlexibleContexts #-} import Data.Type.Equality import GHC.TypeLits (type (+), type (<=), type (<=?)) import Proof.Propositional (Empty(..)) predSucc :: Empty (n :~: 0) => proxy n -> (n + 1 <=? n + n) :~: 'True predSucc _ = Witness ``` resulted in the following compile-time error: ``` Can't find interface-file declaration for type constructor or class equational-reasoning-0.4.0.0:Proof.Propositional.Empty Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error ``` The probem is, Empty class is provided by separate existing package [^2], but is once defined in hidden module and re-exported from exposed from exposed module. If I expose the module where Empty is originally defined and change the module name passed to lookupModule appropriately, then the first code becomes working as expected. So the question: is there any way to retrieve TyCon information defined in hidden module but exported? [^1]: https://github.com/konn/ghc-typelits-presburger/ [^2]: https://github.com/konn/equational-reasoning-in-haskell -- Hiromi ISHII konn.jinro(a)gmail.com Doctoral program in Mathematics, University of Tsukuba

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linking dlls with relative paths on Windows
by Phyx 25 Jul '16

25 Jul '16

Hi Peter, I forgot to respond to this, if you haven't received an answer to this yet then feel free to open a ticket on the ghc trac and I will take a look as soon as I have working Internet again. I don't know what the status is of this for now, the linked to stackoverfow article should work though. Also 7.10.3 has some issues when loading dependent dlls in the same folder as the main one being loaded when not on the search path. 8.0.1 should be fine. Kind regards, Tamar

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Munich Haskell Meeting, 2016-07-27 @ 19:30 Augustiner Bierhalle
by Christian Neukirchen 25 Jul '16

25 Jul '16

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Wednesday, July 27 at Augustiner Bierhalle (Neuhauser Str.) at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jul-2016/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

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pattern match on forall'ed data
by Corentin Dupont 22 Jul '16

22 Jul '16

Hi all, I'm surprised this doesn't work: data SomeData = forall e. (Typeable e, Eq e) => SomeData e (===) :: (Typeable a, Typeable b, Eq a, Eq b) => a -> b -> Bool (===) x y = cast x == Just y test :: SomeData' -> Bool test (SomeData' e) | e === Nothing = True test _ = False It says Could not deduce (Eq a1) arising from a use of ‘===’ How can I achieve something of the same effect? Thanks Corentin

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Re: [Haskell-cafe] Practical use of Stream's monad instance?
by Olaf Klinke 20 Jul '16

20 Jul '16

As someone else on this list whose name I don't recall put it, there is no choice on whether to make Stream a monad or not. It simply _is_ a monad. Anyone with some CS education hearing 'diagonal of inifinite list of infinite lists' should immediately think of Georg Cantor. import Data.Stream import Data.Ratio type Real = Stream Rational -- approximate a real number by an ascending stream -- of lower bounds. supremum :: Stream Real -> Real supremum = join -- If a stream of reals is index-wise ascending, -- the monad instance for Stream computes its supremum. -- Use this e.g. to compute any mathematical quantity -- defined as a supremum. -- Olaf

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Re: [Haskell-cafe] [Haskell] Function to replace given element in list
by amindfv＠gmail.com 19 Jul '16

19 Jul '16

(Moving to haskell-cafe@ -- haskell@ is only for announcements) > El 19 jul 2016, a las 19:44, David Feuer <david.feuer(a)gmail.com> escribió: > > A zipper is a good way to separate the search from the replacement. But the problem at hand does not require such a separation! If you don't need that, a zipper seems like overkill. > > > On Jul 19, 2016 7:39 PM, "Carl Folke Henschen Edman" <carledman(a)gmail.com> wrote: > On Tue, Jul 19, 2016 at 6:13 PM, David Feuer <david.feuer(a)gmail.com> wrote: >> Using a zipper will not get you very far here. The best way would >> likely be to replace the list with a balanced search tree. > > > That depends on the pattern of access and usage. For some a zippered list will outperform a self-balancing tree and vice versa. For others a zippered tree, or something else, will beat either. But when seeing the pattern of changing a single element in the middle of a list, a zippered list is the first improved data structure that comes to mind. > > > Carl Edman > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

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Local Haskell talk in Leipzig, 27 July 2016 at 3:30pm in HTWK
by Heinrich Apfelmus 19 Jul '16

19 Jul '16

Dear (filter (`livesInOrCloseTo` Leipzig_Germany) haskellers), we would like to invite you to a talk by Stephen Blackheath "They why and how of Functional Reactive Programming with Java/Sodium" on Wednesday, 27 July 2016, at 15:30 Uhr in Room Gu 102, Gutenberg-Bau, HTWK Leipzig Abstract: <https://portal.imn.htwk-leipzig.de/termine/vortrag-the-why-and-how-of-funct… Geographical coordinates: <http://www.openstreetmap.org/?mlat=51.31248&mlon=12.37498#map=18/51.31248/1…> Afterwards (~ 17:00 Uhr) there will be a get-together in the Cafe Suedbrause <http://suedbrause.de>. Stop Listening! Johannes Waldmann and Heinrich Apfelmus

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parsec get line number of lexems
by Olivier Duhart 19 Jul '16

19 Jul '16

hello, I am experimenting with parsec. I am building a very simple language. I have a (almost) wholy funcrionning language : syntactic check, AST building and byte code génération. Now i want to improve error checking (type checking more precisely). this should be done on the AST basis. but in the ast i lose the line number information for precise error message. so my question is : is ther a way to get the line numbers at parsers level ? i would then store it in the ast for semantic check purpose thanks for your answers Olivier

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Call for Participation: ICFP 2016
by Lindsey Kuper 19 Jul '16

19 Jul '16

[ Early registration ends 17 August. ] ===================================================================== Call for Participation ICFP 2016 21st ACM SIGPLAN International Conference on Functional Programming and affiliated events September 18 - September 24, 2016 Nara, Japan http://conf.researchr.org/home/icfp-2016 ===================================================================== ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. The conference covers the entire spectrum of work, from practice to theory, including its peripheries. A full week dedicated to functional programming: 1 conference, 1 symposium, 10 workshops, tutorials, programming contest results, student research competition, and mentoring workshop * Overview and affiliated events: http://conf.researchr.org/home/icfp-2016 * Program: http://conf.researchr.org/program/icfp-2016/program-icfp-2016 * Accepted Papers: http://conf.researchr.org/track/icfp-2016/icfp-2016-papers#event-overview * Registration is available via: https://regmaster4.com/2016conf/ICFP16/register.php Early registration is due 17 August, 2016. * Programming contest, 5-8 August, 2016: http://2016.icfpcontest.org/ * Student Research Competition (deadline: 3 August, 2016): http://conf.researchr.org/info/icfp-2016/student-research-competition * Follow @icfp_conference on twitter for the latest news: http://twitter.com/icfp_conference There are several events affiliated with ICFP: Sunday, September 18 Workshop on Higher-order Programming with Effects Workshop on Type-Driven Development Scheme and Functional Programming Workshop Programming Languages Mentoring Workshop Monday, September 19 – Wednesday, September 21 ICFP Thursday, September 22 Haskell Symposium – Day 1 ML Family Workshop Workshop on Functional High-Performance Computing Commercial Users of Functional Programming – Day 1 Friday, September 23 Haskell Symposium – Day 2 OCaml Workshop Erlang Workshop Commercial Users of Functional Programming – Day 2 Saturday, September 5 Commercial Users of Functional Programming – Day 3 Haskell Implementors Workshop Functional Art, Music, Modeling and Design Conference Organizers General Co-Chairs: Jacques Garrigue, Nagoya University Gabriele Keller, University of New South Wales Program Chair: Eijiro Sumii, Tohoku University Local Arrangements Co-Chairs: Shinya Katsumata, Kyoto University Susumu Nishimura, Kyoto University Industrial Relations Chair: Rian Trinkle, Obsidian Systems LLC Workshop Co-Chairs: Nicolas Wu, University of Bristol Andres Loeh, Well-Typed LLP Programming Contest Chair: Keisuke Nakano, The University of Electro-Communications Student Research Competition Chair: David Van Horn, University of Maryland, College Park Mentoring Workshop Co-Chairs: Amal Ahmed, Northeastern University Robby Findler, Northwestern University Atsushi Igarashi, Kyoto Universty Publicity Chair: Lindsey Kuper, Intel Labs Video Chair: Iavor Diatchki, Galois Jose Calderon, Galois Student Volunteer Co-Chairs: Yosuke Fukuda, Kyoto University Yuki Nishida, Kyoto University Gabriel Scherer, INRIA Industrial partners: Platinum partners Jane Street Capital Ahrefs Gold partners Mozilla Research Silver partners Ambiata Tsuru Capital Bronze partners Awake Networks Microsoft Research =====================================================================

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ANN: blockhash-0.1.0.0
by KwangYul Seo 19 Jul '16

19 Jul '16

Hi all! I'm pleased to announce the first release of blockhash, a perceptual image hash calculation tool based on algorithm described in Block Mean Value Based Image Perceptual Hashing by Bian Yang, Fan Gu and Xiamu Niu. https://hackage.haskell.org/package/blockhash https://github.com/kseo/blockhash Program: Usage: blockhash [-q|--quick] [-b|--bits ARG] filenames blockhash Available options: -h,--help Show this help text -q,--quick Use quick hashing method -b,--bits ARG Create hash of size N^2 bits. Library: import qualified Codec.Picture as P import Data.Blockhash import qualified Data.Vector.Generic as VG import qualified Data.Vector.Unboxed as V printHash :: FilePath -> IO () printHash :: filename = do res <- P.readImage filename case res of Left err -> putStrLn ("Fail to read: " ++ filename) Right dynamicImage -> do let rgbaImage = P.convertRGBA8 dynamicImage pixels = VG.convert (P.imageData rgbaImage) image = Image { imagePixels = pixels , imageWidth = P.imageWidth rgbaImage , imageHeight = P.imageHeight rgbaImage } hash = blockhash image 16 Precise putStrLn (show hash) For further information on the blockhash algorithm, please visit the web site: http://blockhash.io/ Thanks, Kwang Yul Seo

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