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ANN: flexiwrap-0.1.0 etc.
by Iain Alexander 24 Sep '11

24 Sep '11

New versions of the package flexiwrap (supplying flexible wrappers for instance selection) and related packages have been released to Hackage. flexiwrap-0.1.0 data-type-0.1.0 function-combine-0.1.0 flexiwrap-smallcheck-0.0.1 flexiwrap version 0.1.0 supports instances of many additional classes for FlexiWrap, and improved documentation, although much remains to be done - more class instances for FlexiWrap, and other wrappers, and more documentation. data-type version 0.1.0 adds a proxy type Data.Type.Proxy. function-combine version 0.1.0 updates its dependencies to support the new version of data-type. flexiwrap-smallcheck version 0.1.0 is a new package supplying support for instances of Serial for FlexiWrap, for use with the smallcheck package. Support for Serial instances for other wrappers is outstanding. Regards, Iain. -- ia(a)stryx.demon.co.uk

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Standard 'decorator' class?
by Jacques Carette 23 Sep '11

23 Sep '11

Has a class like class Decoration t where type Datum t :: * value :: t -> Datum t been defined in any of the haskell packages on hackage? [There are so many variants on naming, it is rather difficult to search for this] Jacques

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Re: [Haskell-cafe] Fwd: problem with cabal install MissingH-1.1.1.0
by Tom Murphy 23 Sep '11

23 Sep '11

I used to have a lot of cabal problems when running a version of the GHC installed with MacPorts. I notice you're using homebrew. Maybe that's part of the problem? Tom On Sep 22, 2011 8:11 PM, "Mariano Cortesi" <mcortesi(a)gmail.com> wrote:

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[ANNOUNCE] skein-0.1: Skein, a family of cryptographic hash functions. Includes Skein-MAC as well.
by Felipe Almeida Lessa 23 Sep '11

23 Sep '11

Hello! I'm pleased to announce the first version of the skein package [1]! Skein is a family of fast secure cryptographic hash functions [2]. The skein package provides high-level bindings (using crypto-api [3]) to the optimized Skein C library. Currently we support Skein as a hash function and also Skein as a message authentication code (MAC). The code is well-documented with examples and has many known answer tests (KATs). It currently lives on patch-tag [4]. Hackage will be build the docs soon enough. Meanwhile, here's a short example: Prelude> :s -XOverloadedStrings Prelude> :m Crypto.Skein Crypto.Classes Data.ByteString.Char8 Data.Serialize Prelude Crypto.Skein Crypto.Classes Data.ByteString.Char8 Data.Serialize> encode (hash' "Haskell" :: Skein_512_512) "b\227\213t\170\GS\131w\151\240\160\183\205\US\169\138\&6\239\215\156\227\SI\234\142P\132\182\SOH\180t\203b\147\190\DLE{\168\214\DC1\238\232y\168\161s\207\172\216\a\202\130c$\SYN\asD<\151\201D\138A\SUB" Prelude Crypto.Skein Crypto.Classes Data.ByteString.Char8 Data.Serialize> encode (skeinMAC' "secretkey" "Haskell" :: Skein_512_512) "_i>.Z\129\ENQ\217L\t9BZ\220\163c&9#\135\234A{\181\&2*\149\STX\216_\DC43\bF\189\196D\r ;\208\EOT}\ENQY\147\232\244e/;4\212!\224\US\138\138\234q=1\129\244" Enjoy! =D [1] http://hackage.haskell.org/package/skein [2] http://swww.skein-hash.info/ [3] http://hackage.haskell.org/package/crypto-api [4] https://patch-tag.com/r/felipe/skein/ -- Felipe.

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Package versioning policy - Harmless type changes?
by Heinrich Apfelmus 23 Sep '11

23 Sep '11

Dear all, the package versioning policy specifies that changing the type of any entity makes a change of the B number in A.B.C necessary. However, it seems to me that a small selection of type changes don't break dependent code. In particular, consider the following example, where I drop a Typeable class constraint: - foo :: Typeable a => AddHandler a -> NetworkDescription (Event a) + foo :: AddHandler a -> NetworkDescription (Event a) Can removing a type class constraint on a function break dependent code? Should I change the B number or just the C in version A.B.C when introducing this change? Best regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com

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regex-applicative library needs your help! (algorithmic challenge)
by Roman Cheplyaka 23 Sep '11

23 Sep '11

Please help make the regex-based parsing library efficient! https://github.com/feuerbach/regex-applicative/wiki/Call-For-Help -- Roman I. Cheplyaka :: http://ro-che.info/

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Quick check finite data generation
by mukesh tiwari 23 Sep '11

23 Sep '11

Hello all I have a data type data Index = Index {indexSize::Float, indexIds::[Int], indexDown::(IntMap.IntMap Index)} | IndexLeaf {indexSize::Float, indexIds::[Int]} | IndexEmpty {indexSize::Float} deriving ( Show , Eq ) I derived some thing like this for QuickCheck testing instance Arbitrary a => Arbitrary ( IntMap a ) where arbitrary = liftM IntMap.fromList arbitrary instance Arbitrary Index where arbitrary = oneof [ liftM3 Index arbitrary arbitrary arbitrary , liftM2 IndexLeaf arbitrary arbitrary , liftM IndexEmpty arbitrary ] but its generating infinite list of data. After reading the paper QuickCheck: A Lightweight Tool for Random Testing of Haskell Programs<http://www.eecs.northwestern.edu/%7Erobby/courses/395-495-2009-fall/quick.p…> <http://www.eecs.northwestern.edu/%7Erobby/courses/395-495-2009-fall/quick.p…> i tried to write above one using sized but i am not sure how to write this . instance Arbitrary a => Arbitrary ( IntMap a ) where arbitrary = liftM IntMap.fromList arbitrary instance Arbitrary Index where arbitrary = sized arbIndex arbIndex 0 = liftM IndexEmpty arbitrary arbIndex 1 = liftM2 IndexLeaf arbitrary arbitrary arbIndex n = frequency [ ( 1 , liftM IndexEmpty arbitrary ) , ( 1 , liftM2 IndexLeaf arbitrary arbitrary ) , ( 2 , liftM2 Index arbitrary arbitrary ( arbIndex $ div n 2 ) ) ] but from this type i can see arbIndex $ div n 2 will return Gen Index not Gen ( IntMap Index ) and i am getting compiler error . Could some one please tell me , how to write arbIndex n in terms of smaller n like in the paper arbTree 0 = liftM Leaf arbitrary arbTree n = frequency[ ( 1 , liftM Leaf arbitrary ) , ( 4 , liftM2 Branch ( arbTree $ div n 2 ) ( arbTree $ div n 2 ) ) ] Thank You Mukesh Tiwari

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ANN: New releases in the lightweight monadic regions family
by Bas van Dijk 23 Sep '11

23 Sep '11

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problem with cabal install MissingH-1.1.1.0
by Mariano Cortesi 22 Sep '11

22 Sep '11

Hi, My name is mariano and I'm quite new to haskell. I trying to setup up my environment and use the eclipse plugin for haskell. But is not working property because, it tries to compile the scion browser and this depends on MissingH which fails on build. I'm with mac OS X lion, ghc version 7.2.1 and when a i try to install MissingH version 1.1.1.0 it fails with [24 of 47] Compiling Data.BinPacking ( src/Data/BinPacking.hs, dist/build/Data/BinPacking.o ) src/Data/BinPacking.hs:45:6: Illegal datatype context (use -XDatatypeContexts): (Num size, Ord size, Show size, Show obj) => cabal: Error: some packages failed to install: MissingH-1.1.1.0 failed during the building phase. The exception was: ExitFailure 1 Any ideas? I don't know what to do :S best, Mariano

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Re: [Haskell-cafe] Quickcheck, Arbitrary and Overlapping instances
by Valentin Robert 22 Sep '11

22 Sep '11

I think it is one case where you should use newtype instead of type, so that it is not just a simple type synonym, but an actual "other" type. With type, you're just making an alias, but Haskell sees the same type. A newtype wrapper will hide this, at the price of having to define a (unique) constructor... So yes, you'll have to change some code.

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Proposal: Subcomputations in arrow notation
by Ertugrul Soeylemez 22 Sep '11

22 Sep '11

Hello fellow Haskellers, this is a proposal to extend the arrow notation (-XArrows). I find myself writing the following very often: system :: Wire IO () String system = proc _ -> do botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event addBot -< (botAddPeriod, botAddSpeed, botAddStart) bots <- manager -< ((), maybe MgrNop id botMsg) let botStr = concatMap (printf "%8.2") . M.elems $ bots :: String identity -< printf "Bot positions: %s" botStr where addBot :: Wire IO (Double, Double, Double) (MgrMsg Int IO () Double) addBot = proc (addPeriod, addSpeed, addStart) -> do periodically -< addPeriod botId <- identifier -< () identity -< MgrAdd botId (constant addSpeed >>> integral addStart) The relevant part is the first paragraph of the first arrow computation: botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event addBot -< (botAddPeriod, botAddSpeed, botAddStart) This line should generate a message for the bot manager at random intervals. The actual event generator is in the second arrow computation 'addBot'. I would like to be able to write this more in line with the rest of the code. The following is possible: system :: Wire IO () String system = proc _ -> do botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event (proc (addPeriod, addSpeed, addStart) -> do periodically -< addPeriod botId <- identifier -< () identity -< MgrAdd botId (constant addSpeed >>> integral addStart)) -< (botAddPeriod, botAddSpeed, botAddStart) bots <- manager -< ((), maybe MgrNop id botMsg) let botStr = concatMap (printf "%8.2") . M.elems $ bots :: String identity -< printf "Bot positions: %s" botStr This is probably not a big improvement. It's more concise, but also harder to understand. My proposal is to add syntax to allow the following notation: system :: Wire IO () String system = proc _ -> do botAddPeriod <- succ ^<< noise -< () botAddSpeed <- noise1 -< () botAddStart <- noise1 -< () botMsg <- event $ do periodically -< addPeriod botId <- identifier -< () identity -< MgrAdd botId (constant addSpeed >>> integral addStart) bots <- manager -< ((), maybe MgrNop id botMsg) let botStr = concatMap (printf "%8.2") . M.elems $ bots :: String identity -< printf "Bot positions: %s" botStr Again the relevant part is the event generator in the middle. In this hypothetical syntax, the compiler would figure out from the inner computation, which variables from the outer scope are used and pass them automatically in an appropriate tuple. You wouldn't need any explicit passing anymore. If others like the idea, too, and there is nobody to implement it, then I would be willing to get in touch with the GHC code and implement this as a patch myself. What do you think? Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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New: A French translation of Learn You A Haskell for Great Good!
by Valentin ROBERT 22 Sep '11

22 Sep '11

Hello everyone, I've decided to translate the famous Learn You a Haskell for Great Good in French a few weeks ago, and I'm pleased to share it with you all today! Well, especially with the French-speaking community, but I guess everyone should be aware of its existence, in case you ever encounter a French newbie and want to redirect him to some French resources. So here it is: http://lyah.haskell.fr You will also notice that I did register a domain name for this, and will try to provide other information on Haskell in French at the same place. For instance, I created a wiki which contains basic information, available here: http://haskell.fr All French-speaking Haskell enthusiasts (Haskelletors? :D) are welcome to participate in this wiki in any way they can think of. I doubt this will be as useful as the HaskellWiki, but if we can have a few introductions to some subjects in French, pointing to more comprehensive resources in English, I guess it'll be good enough. Oh, I also created the less-inspired logo ever out of the usual Haskell logo! :) Any feedback on whether these are good ideas or not, and what could be done better, would be greatly appreciated. Big thanks to Miran Lipovača for writing the original LYAH (well, except for the jokes that were hard to translate/adapt!), and to the few people on #haskell-fr for somehow deciding me to actually do this. Also, thanks to my anonymous proof-reader, who did a great job I believe! And since Brent allowed me to, French monads are now officially like crêpes! - Valentin "Ptival" Robert

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Re: [Haskell-cafe] Evaluating type expressions in GHCi
by Brandon Moore 22 Sep '11

22 Sep '11

>From: Sean Leather <leather(a)cs.uu.nl> > >I would like to ask GHCi for the type that a type expression will evaluate to, once all definitions of type synonyms and (when possible) type families have been inlined. > > >It appears that I can do some part of this for type T by using ":t undefined :: T": ... >undefined :: F (Int, Bool) :: (Bool, Int) > >I also get what I expect here: > >ghci> :t undefined :: F (a, Bool) >undefined :: F (a, Bool) :: (F a, Int) > >Of course, this doesn't work on types of kinds other than *. In the absence of interpreter support, you can work around that by making appropriate type constructors. {-# LANGUAGE TypeFamilies, KindSignatures, EmptyDataDecls #-} type family G a :: * -> * type instance G Int = Maybe type instance G Bool = [] data Wrap1 (t :: * -> *) ghci> :t undefined :: Wrap1 (G Int) undefined :: Wrap1 (G Int) :: Wrap1 Maybe The development version of ghci seems to support type declarations, which would make this easier. https://github.com/ghc/ghc/commit/3db757241ce7fb99c096c30481aefa86bb9855a1 Brandon

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Haskell Weekly News: Issue 200
by Daniel Santa Cruz 22 Sep '11

22 Sep '11

Welcome to issue 200 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of September 11 to 17, 2011. You can find the HTML version of this issue at: http://contemplatecode.blogspot.com/2011/09/haskell-weekly-news-issue-200.h… Announcements Chris Smith is exploring the interest of holding a Virtual Hackathon, using Google+ and a Wiki. Come check it out if you would be interested in being part of it! [1] http://goo.gl/lWnea Valentin Robert has completed Apprendre Haskell vous fera le plus grand bien!, a translation of Learn You a Haskell for Great Good! into French, and has also created a wiki page with basic information about Haskell for the French speaking world. Kudos to Valentin for his work on this project! [2] http://goo.gl/ixiXW [3] http://goo.gl/1CG7j New and Updated Projects * netwire (Ertugrul Soeylemez; 1.2.5) Multiple major and minor changes. [4] http://goo.gl/DS4QR * webwire (Ertugrul Soeylemez; 0.1.0) An experimental web framework based on the functional reactive programming library netwire. [5] http://goo.gl/DS4QR * numerals (Roel van Dijk) Contains functions to convert numbers to words in a number of languages. [6] http://goo.gl/4YfhK * splaytree (Jehn Lato; 0.1) Provides splay tree based implementations of Sets, Seqs, and RangeSets. [7] http://goo.gl/aQfX5 * qrcode (Chris Yuen) Intended to be a full featured QR Code library with encoding and decoding and other advanced features. [8] http://goo.gl/pymtr * haskdogs (Sergey Mironov; 0.1) Project-level ctag file generator. [9] http://goo.gl/SA6cx Quotes of the Week * Jafet: Can oleg create a term so complicated that even he could not type-check it? * ion: let es = ["vim", "emacs", "nano"] in map (\e -> intercalate " and " (delete e es) ++ " suck, learn " ++ e) es * cmccann: [on using SomeException] just catch all exceptions, then ignore them. it's the industry-proven way * kmc: une monade est comme une crepe. una monada es como un burrito. eine Monade ist wie ein Strudel. * dylukes: I learned PBMMPPULCDADMABRRRBBBLLTAAMMBBC. It's the operator precedence of C. * benmachine: ozataman: does it have a main, or a thing with type IO thing which looks sort of mainish? Top Reddit Stories * Categorized Weaknesses from the State of Haskell 2011 Survey Domain: nickknowlson.com, Score: 72, Comments: 42 On Reddit: [10] http://goo.gl/0h0K5 Original: [11] http://goo.gl/DZB5V * Haskell B. Curry, born Sept. 12, 1900 Domain: en.wikipedia.org, Score: 69, Comments: 17 On Reddit: [12] http://goo.gl/FYP0F Original: [13] http://goo.gl/S520L * The Records problem in Haskell - help build a consensus about how to fix it, finally Domain: hackage.haskell.org, Score: 59, Comments: 132 On Reddit: [14] http://goo.gl/8cZnI Original: [15] http://goo.gl/VuVoQ * Wrriten in Haskell: The Dynamic Scheduling System for the Green Bank Telescope Domain: self.haskell, Score: 51, Comments: 4 On Reddit: [16] http://goo.gl/vaD3C Original: [17] http://goo.gl/vaD3C * Announcing: Sirkel, a Haskell implementation of the Chord DHT with fault tolerance and replication! Domain: mortenlysgaard.com, Score: 36, Comments: 1 On Reddit: [18] http://goo.gl/VNpSv Original: [19] http://goo.gl/05NIn * Not going to ICFP? Here's an excuse for you Domain: ro-che.info, Score: 30, Comments: 5 On Reddit: [20] http://goo.gl/ABvsq Original: [21] http://goo.gl/uI2Mj * Announce: Yesod 0.9.2 - Everything Just Works Domain: yesodweb.com, Score: 24, Comments: 2 On Reddit: [22] http://goo.gl/izCme Original: [23] http://goo.gl/H0bLr * A play in one act Domain: hpaste.org, Score: 24, Comments: 17 On Reddit: [24] http://goo.gl/OLncN Original: [25] http://goo.gl/lcssv * HaTeX 3 - New version of the Haskell LaTeX library. Domain: deltadiaz.blogspot.com, Score: 20, Comments: 6 On Reddit: [26] http://goo.gl/AgAOp Original: [27] http://goo.gl/4z7nJ * Open Quark: Another haskell like language on JVM. Much more older and mature than Frege. Yet unknown and forgotten. Domain: openquark.org, Score: 19, Comments: 6 On Reddit: [28] http://goo.gl/6Lfx6 Original: [29] http://goo.gl/BI0mC Top StackOverflow Questions * Proving “no corruption” in Haskell votes: 17, answers: 3 Read on SO: [30] http://goo.gl/Xclnk * How to handle feature requests that add new package dependencies votes: 13, answers: 3 Read on SO: [31] http://goo.gl/Gw6HQ * Left and Right Folding over an Infinite list votes: 12, answers: 4 Read on SO: [32] http://goo.gl/YKHlB * Shorter way to write this code votes: 11, answers: 6 Read on SO: [33] http://goo.gl/7ZmBZ * Can't link OpenCL on Windows with GHC votes: 10, answers: 1 Read on SO: [34] http://goo.gl/AnvJo * What's the point of 'const' in the Haskell Prelude? votes: 10, answers: 4 Read on SO: [35] http://goo.gl/g04xE * Haskell functional dependency conflict votes: 9, answers: 2 Read on SO: [36] http://goo.gl/ksmM0 * DatatypeContexts Deprecated in Latest GHC: Why? votes: 9, answers: 2 Read on SO: [37] http://goo.gl/R03pa * Clojure equivalent of Haskell's “Scrap Your Boilerplate” (SYB) votes: 8, answers: 1 Read on SO: [38] http://goo.gl/R6NoS * Why using functions defined in the same module faster than the same function defined in another? votes: 8, answers: 2 Read on SO: [39] http://goo.gl/qAjCk * repeatedly applying a function until the result is stable votes: 8, answers: 4 Read on SO: [40] http://goo.gl/NlP4u About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92438 2. http://lyah.haskell.fr/ 3. http://haskell.fr/ 4. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92414 5. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92414 6. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92426 7. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18934 8. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92433 9. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92353 10. http://nickknowlson.com/blog/2011/09/12/haskell-survey-categorized-weakness… 11. http://www.reddit.com/r/haskell/comments/kd2ky/categorized_weaknesses_from_… 12. http://en.wikipedia.org/wiki/Haskell_Curry 13. http://www.reddit.com/r/haskell/comments/kcq8m/haskell_b_curry_born_sept_12… 14. http://hackage.haskell.org/trac/ghc/wiki/Records 15. http://www.reddit.com/r/haskell/comments/kgd4g/the_records_problem_in_haske… 16. http://www.reddit.com/r/haskell/comments/ke3ho/wrriten_in_haskell_the_dynam… 17. http://www.reddit.com/r/haskell/comments/ke3ho/wrriten_in_haskell_the_dynam… 18. http://mortenlysgaard.com/?p=35 19. http://www.reddit.com/r/haskell/comments/kilx4/announcing_sirkel_a_haskell_… 20. http://ro-che.info/ccc/13.html 21. http://www.reddit.com/r/haskell/comments/kc4aa/not_going_to_icfp_heres_an_e… 22. http://www.yesodweb.com/blog/2011/09/yesod-0.9.2 23. http://www.reddit.com/r/haskell/comments/kc6h2/announce_yesod_092_everythin… 24. http://hpaste.org/51474 25. http://www.reddit.com/r/haskell/comments/kixek/a_play_in_one_act/ 26. http://deltadiaz.blogspot.com/2011/09/hatex-3-previous-notes.html 27. http://www.reddit.com/r/haskell/comments/kflnp/hatex_3_new_version_of_the_h… 28. http://openquark.org/Welcome.html 29. http://www.reddit.com/r/haskell/comments/kgtxm/open_quark_another_haskell_l… 30. http://stackoverflow.com/questions/7435363/proving-no-corruption-in-haskell 31. http://stackoverflow.com/questions/7436939/how-to-handle-feature-requests-t… 32. http://stackoverflow.com/questions/7396978/left-and-right-folding-over-an-i… 33. http://stackoverflow.com/questions/7453744/shorter-way-to-write-this-code 34. http://stackoverflow.com/questions/7391634/cant-link-opencl-on-windows-with… 35. http://stackoverflow.com/questions/7402528/whats-the-point-of-const-in-the-… 36. http://stackoverflow.com/questions/7436109/haskell-functional-dependency-co… 37. http://stackoverflow.com/questions/7438600/datatypecontexts-deprecated-in-l… 38. http://stackoverflow.com/questions/7376572/clojure-equivalent-of-haskells-s… 39. http://stackoverflow.com/questions/7401724/why-using-functions-defined-in-t… 40. http://stackoverflow.com/questions/7442892/repeatedly-applying-a-function-u…

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Monad Laws and Do Notation
by diazepan 22 Sep '11

22 Sep '11

I've got this expression expression = do w <- "hello" y <- "to you" return w I wanna know how can I reduce it using monad laws -- View this message in context: http://haskell.1045720.n5.nabble.com/Monad-Laws-and-Do-Notation-tp4828598p4… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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ghc 7.0.3 view patterns and exhaustiveness
by Richard Cobbe 21 Sep '11

21 Sep '11

I'm starting to play around with GHC's support for view patterns, and I'm running into what appears to be an annoying limitation of the implementation. GHC 7.0.3 (32-bit), MacOS 10.6.8. First module; defines an abstract type & provides a (trivial) view for it. module Term(Term, TermView(..), view) where data Term = TVar String | TApp Term Term | TLam String Term data TermView = Var String | App Term Term | Lam String Term view :: Term -> TermView view (TVar x) = Var x view (TApp rator rand) = App rator rand view (TLam x body) = Lam x body Second module tries to use the view in a trivial function: {-# LANGUAGE ViewPatterns #-} module Client where import Term numVarRefs :: Term -> Integer numVarRefs (view -> Var _) = 1 numVarRefs (view -> App rator rand) = numVarRefs rator + numVarRefs rand numVarRefs (view -> Lam _ body) = numVarRefs body -- numVarRefs (view -> _) = error "bogus" f :: TermView -> Integer f (Var _) = 1 f (App rator rand) = f (view rator) + f (view rand) f (Lam _ body) = f (view body) GHCI complains when trying to load this second module: Client.hs:8:1: Warning: Pattern match(es) are non-exhaustive In an equation for `numVarRefs': Patterns not matched: _ (I have ":set -fwarn-incomplete-patterns" in my .ghci.) I wrote 'f' to make sure that my patterns for TermView are indeed exhaustive, and GHC doesn't complain about it all. If I uncomment the last definition for numVarRefs, the warning goes away. I did some searching around on the web, in the mailing list archives, and in the GHC bug database, and I see that early on, views had trouble giving useful diagnostics for overlapping or non-exhaustive patterns, but most of those problems seem to have been fixed. I also couldn't find a bug report for precisely this situation -- #4439 is the closest, but I'm not using existential types here at all. Should I file a bug, or am I overlooking something simple? Or is this a known limitation of the current implementation? Thanks, Richard

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stack overflow pain
by Tim Docker 21 Sep '11

21 Sep '11

I'm getting a stack overflow exception in code like this: -- applyAction :: A -> IO [B] .... vs <- fmap concat $ mapM applyAction sas return vs I don't get it if I change the code to this: -- applyAction :: A -> IO [B] .... mapM_ applyAction sas return [] But of course, I need the results from the actions. I know that the returned list contains approximately 1 million items. Any suggestions on how I should rewrite the first code snippet to not blow the stack? I do find debugging stack overflow errors quite difficult - with little information from the runtime I'm often left guessing which parts of a large codebase might be causing them. Note that there's plenty of heap space available, it's the evaluation stack that is being used up. I could run with -K to increase the size of the stack, but if possible I'd rather solve this in the code. Thanks for any pointers. Tim

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hackage library info
by kioto mitsubisi 21 Sep '11

21 Sep '11

Hi, I want to ask a question about hackage which contains additional libraries to Haskell. Is there a mechanism that will help developer to choose a library among the others? I mean, there are several packages that may do the same thing in hackage and to choose one among the others, developer may want to have more information about the library such as other developers' ratings and comments, activity of development of the library, etc so that one can choose the better alternative. Is there a mechanism for that or is there a plan to add these to the hackage? Thanks

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poles/residues -> FIR tap weights ?
by Captain Freako 21 Sep '11

21 Sep '11

Anyone know of a Haskell package containing a function for converting a list of pole/residue pairs into FIR filter tap weights? Thanks, -db

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Parsec line number off-by-one
by Ben Gamari 21 Sep '11

21 Sep '11

Recently I've been playing around with Parsec for a simple parsing project. While I was able to quickly construct my grammar (simplified version attached), getting it working has been a bit tricky. In particular, I am now stuck trying to figure out why Parsec is mis-reporting line numbers. Parsec seems convinced that line 12 of my input (also attached) has a "%" character, $ runghc Test.hs Left "(unknown)" (line 12, column 1): unexpected "%" expecting space or atom name while my file clearly disagrees, 10 %FLAG ATOM_NAME 11 %FORMAT(20a4) 12 C1 H1 C2 H2 C3 H3 C4 H4 C5 C6 C7 C8 N1 C9 H9 C10 H10 C11 H11 C12 13 H12 C13 H13 C14 C15 N2 C16 C17 C29 H18 C19 H19 C20 H20 C21 H21 C22 H221H222H223 ... 18 %FLAG CHARGE 19 %FORMAT(5E16.8) The task here is to identify the block of data lines (lines 12-17), ending at the beginning of the next block (starting with "%"). It seems likely that my problem stems from the fact that I use "try" to accomplish this but this is as far as I can reason. Any ideas what might cause this sort of off-by-one? Does anyone see a better (i.e. working) way to formulate my grammar? Any and all help would be greatly appreciated. Thanks. Cheers, - Ben

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Re: [Haskell-cafe] instance Enum Double considered not entirely great?
by John Lato 21 Sep '11

21 Sep '11

> From: Casey McCann <cam(a)uptoisomorphism.net> > <CAJ5riwLLu=wAFXm8VPnqRG2Daxxgf=UpgxzCHydMeBGNgixTFQ(a)mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > On Tue, Sep 20, 2011 at 8:20 PM, Daniel Fischer > <daniel.is.fischer(a)googlemail.com> wrote: > >> However, nowadays I tend to think that making the Eq and Ord instances >> well-behaved (wrt the class contract) and having separate IEEE comparisons >> would overall be preferable. >> There is still the question whether all NaNs should be considered equal or >> not [and where Ord should place NaNs]. > > IEEE semantics are incompatible with Ord regardless. The problem can > be fixed by changing Ord, removing the instance completely, or > changing the instance to ignore the IEEE spec. I think the latter is > the least bad option in the big picture. > > I still don't see why it makes sense to add separate IEEE comparisons > instead of just adding a standard partial order class, though. Surely > posets are common enough to justify the abstraction, and it surprises > me that one isn't already included. No doubt there are at least three > or four different partial ordering classes on Hackage already. I agree with this already, and will agree more strongly if ConstraintKinds become widely available. > >> Google suggests "Exception for NaN" from May. > > Ah, yes, wherein someone suggested that comparing to NaN should be a > runtime error rather than give incorrect results. A strictly more > correct approach, but not one I find satisfactory... I would consider this better than the current situation. At least your sets wouldn't be silently corrupted. John L.

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Re: [Haskell-cafe] Strange No instance error with cabal install
by Rune Harder Bak 21 Sep '11

21 Sep '11

Sorry, forgot to send to the list, But everything works today, and the commit was pulled from aeson to aeson-native, so that must have been it. Thanks! On Wed, Sep 21, 2011 at 8:20 AM, Rune Harder Bak <rune(a)bak.dk> wrote: > So you are saying, that this is basically because he has other version > of different packages, > not providing the same instances, that makes sense. > The other problem was no instance for Default (Request R) (Request > from Network.Wai) > It was provided by http-enumerator, but maybe not in his version of the package. > > I tried with aeson-native after you post without look, but I see a new > one has been released now. > Going to try it today. > Thanks! > > > On Tue, Sep 20, 2011 at 2:00 PM, Roel van Dijk <vandijk.roel(a)gmail.com> wrote: >> I see the aeson version with the stricter dependency on deepseq < 1.2 >> is now also released on hackage: >> >> http://hackage.haskell.org/package/aeson-0.3.2.12 >> >

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Typhoon
by Kazu Yamamoto 21 Sep '11

21 Sep '11

Hello, To those who are in Tokyo for ICFP: The typhoon is likely to come after 16:00 today. Many students and workers will go home earlier this afternoon. It's Japanse style. If typhoon comes, umbrella does not work. Please stay in your building. You should understand all traffic transportation will stop. Even blackout would happen. Please please don't underestimate the typhoon. Typhoon info: http://www.jma.go.jp/en/typh/ http://weathernews.jp/satellite/ Rain visual info: http://tokyo-ame.jwa.or.jp/en/index.html Please don't panic. Stay in your building for about two hours. Enjoy slow life. --Kazu

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Animas/Yampa - Using Zip as a Routing Function in a Parallel Switch with Feedback
by M. George Hansen 21 Sep '11

21 Sep '11

Greetings, I've been playing around with functional reactive programming using Animas/Yampa and ran into a strange situation. I'm using a parallel switch to route input to a collection of signal functions and using the output as feedback (to simulate state). Everything works as expected until I attempt to use zip as a routing function (i.e. pair each element of input with a signal function). Using zip as a routing function causes the program to enter an infinite loop when it evaluates the output from the parallel switch. Here is a minimal program that fails to terminate when using zip as a routing function: ----------------------------------------------------------------------------------------- {-# LANGUAGE Arrows #-} module LoopingTest ( ) where import Control.Arrow import FRP.Animas main = embed (process []) ([42], []) process :: [Activity] -> SF [InputEvent] SystemOutput process activities = proc inputEvents -> do rec let senses = map (\state -> (inputEvents, state)) states states <- par route activities -< senses returnA -< states route :: [Sense] -> [sf] -> [(Sense, sf)] -- route a sfs = fmap (\sf -> (head a, sf)) sfs route = zip type Activity = SF Sense State type InputEvent = Integer type State = [Integer] type Sense = ([InputEvent], State) type SystemInput = ([InputEvent], [State]) type SystemOutput = [State] ----------------------------------------------------------------------------------------- If you run the main function as-is the program will run forever, but if you change the route function to use the commented definition instead of zip the program terminates normally. I simply cannot wrap my brain around this issue - zip normally works just fine with infinite lists as long as one of the lists is finite, and in this case the number of Activity signal functions is known at compile time to be finite. I can't find anything conceptually wrong with using zip as a routing function either. If anyone has any thoughts I would be very grateful. -- M. George Hansen technopolitica(a)gmail.com

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Fwd: Klocwork eNews: Secure Coding for C/C++
by Vasili I. Galchin 20 Sep '11

20 Sep '11

Hello, I get so frustrated trying to convince managers and colleagues of the efficacy of FPLs. Below speaks volumes about the "type safety" of C and C++. It is a bandaid approach. Vasili --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- ---------- Forwarded message ---------- Date: Tue, Sep 20, 2011 at 9:14 AM Subject: Klocwork eNews: Secure Coding for C/C++ To: vigalchin(a)gmail.com ** [image: Klocwork eNewsletter - September 2011] eLEARNING Secure Coding for C/C++ When it comes to security attacks, the network used to be the prime target. But the attack profile has changed. Now security is a software problem too, with the number of software security vulnerabilities growing every year. As a result, the pressure on software developers to create secure software has never been greater. Brush up on the fundamentals of secure coding with this no charge, interactive eLearning course<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> : - Get the latest secure coding best practices - Learn nine tested secure coding techniques - See how to avoid common buffer overflows *This is a must-see course – view it today!*<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> SOCIAL MEDIA Follow Klocwork Do you know that Klocwork participates in all your favorite social media channels? Get quick updates from us and see what we're talking about by following us on Facebook, LinkedIn and Twitter. Check out our recent blog posts and links to our social media pages under the *Follow Us* section on www.klocwork.com<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> . BLOG Join the Discussion *Klocwork University consolidates learning resources into a single roster<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> * Your one stop for self-paced online learning. *Squeezing max from the 'try/finally' blocks<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> * Tips on handling resources in Java. *Importance of MISRA<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> * Klocwork's MISRA support is important to customers. Klocwork | 15 New England Executive Park | Burlington, MA 01803 1.866.556.2967 | www.klocwork.com<http://mkto-d0052.com/track?type=click&enid=bWFpbGluZ2lkPWtsb2N3b3JrQmV0YWN…> © 2011 Klocwork. All rights reserved. If you no longer wish to receive these emails, click on the following link: Unsubscribe<http://resources.klocwork.com/UnsubscribePage.html?mkt_unsubscribe=1&mkt_to…>

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Strange No instance error with cabal install
by Rune Harder Bak 20 Sep '11

20 Sep '11

Sometimes when one of our developers (using Arch-linux) tries to cabal install packages he gets a "no instance for" error. Code that compiles fine on my computer, and other computers I try it on. Even some packages on hackage (trying to install aeson-native for instance gives Data/Aeson/Types.hs:196:22: No instance for (NFData Object) arising from a use of `rnf' Possible fix: add an instance declaration for (NFData Object) In the expression: rnf o In an equation for `rnf': rnf (Object o) = rnf o In the instance declaration for `NFData Value') I tried removing the .ghc and .cabal folder, even reinstalled ghc-7.04 and cabal-install (most recent), but the problem persisted (might not have been a clean install though, I'm no Arch expert) I know this is kind of vauge, and not in she shape of filling a bug report, heck I can't even reproduce the error on my computer. But perhaps somebody else has run in to this strange behavior before? Best, Rune

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ANNOUNCE: lushtags, haskell ctags for Vim Tagbar plugin
by Bit Connor 20 Sep '11

20 Sep '11

I would like to announce the first release of my program lushtags. Available on hackage: cabal install lushtags At github: https://github.com/bitc/lushtags Screenshot: https://github.com/bitc/lushtags/raw/master/doc/screenshot-tagbar-2011-09-1… What is lushtags? From the README: lushtags ======== Create ctags compatible tags files for Haskell programs Similar programs are [hasktags][1], [gasbag][2], [hothasktags][3], and GHC's builtin ctags generation. lushtags differs from these by being designed to have smooth integration with the [Vim Tagbar][4] plugin. Tagbar is nice because it deals with creating tags automatically. There is no need to manually run commands or keep track of tag files. Just open any Haskell file in Vim and the Tagbar window will instantly show an interactive browsable list of all the functions and declarations in the file. This window also updates automatically as you edit the file. The tags created by lushtags are marked with several extensions, so that when used with Tagbar you get these features: - Type signatures are displayed for functions. - Tags are properly scoped so that, for example, data declarations appear as a tree with their constructors scoped as children. - Definitions that are exported from the module are marked as "public" and appear emphasized in Tagbar. - Tag locations are internally stored as patterns, not line numbers, so that you can correctly jump to tags even if they have moved in the source code during editing. ![screenshot](https://github.com/bitc/lushtags/raw/master/doc/screenshot-tagbar-2011-09-19.png) [1]: http://hackage.haskell.org/package/hasktags [2]: http://kingfisher.nfshost.com/sw/gasbag/ [3]: http://hackage.haskell.org/package/hothasktags [4]: http://majutsushi.github.com/tagbar/

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Data.Text.IO.hGetContents problem on windows
by David Virebayre 20 Sep '11

20 Sep '11

Bonjour Café, bonjour Bryan I have a program that works fine on linux, but doesn't on windows. On windows XP with the latest Haskell platform, I get: <socket: 1860>: hFileSize: invalid argument (Bad file descriptor) I think the problem is with hGetContents from Data.Text.IO, but my google-fu failed to help me find any information. Is there something I'm doing wrong ? David. The source code of the part that fails is as follows: -- Execute a command on a distant server using the rexec protocol. rexec :: HostName -- server to connect to -> Text -- user -> Text -- password -> TextEncoding -- server's text encoding -> Text -- command to execute -> IO (Maybe Text) rexec !ip !ru !rp !enc cmd = handle rexec_error $ do hdl <- connectTo ip (PortNumber 512) let end_param = T.singleton (chr 0) ctrl_string = T.concat [ "0", end_param, ru, end_param, rp, end_param, cmd, end_param ] hSetEncoding hdl enc TIO.hPutStr hdl ctrl_string -- make sure the control string is sent. hFlush hdl -- 1st char read is actually a error code which we ignore for now hGetChar hdl !res <- TIO.hGetContents hdl hClose hdl return (Just res) rexec_error :: SomeException -> IO (Maybe Text) rexec_error err = do putStrLn $ show err return Nothing

1 1

Library support for sorting with Text.Data.ICU.Collate.MCollator?
by Richard Cobbe 19 Sep '11

19 Sep '11

I'm trying to sort a list of Text values using a collator obtained from the Text.Data.ICU.Collate module in the text-icu package on Hackage. Unfortunately, I can't use the normal Data.List.sortBy function with one of these collators, because the collators return (IO Ordering), not Ordering. It's easy to write sortWithCollator :: [Text] -> IO [Text], but I'd rather not have to. I haven't been able to find library support for this anywhere -- am I overlooking it, or do I need to write the sort function myself? Thanks, Richard

2 2

The applicative instances for Either?
by Ketil Malde 19 Sep '11

19 Sep '11

Hi, I have a program that makes use of the applicative instance for Either String. I used to define these instances locally, but at some point, they became part of Control.Applicative. I have limited the dependencies to 'base >= 4', but apparently, some version 4s of base include this instance, some do not, and it causes problems for people trying to compile the program. Is there any information, or otherwise accessible source specifying exactly when this was changed, so that I can have more precise dependencies? And is there a simple way to handle this conditionally, either within cabal, or using CPP? -k -- If I haven't seen further, it is by standing in the footprints of giants

4 4

Enumeratees are killing me
by tsuraan 19 Sep '11

19 Sep '11

I'm trying to write what I think should be a simple Enumeratee, but I'm just not having any luck getting it to typecheck, and I'm coming to the realization that I still have no idea what I'm doing. The essential thing I want to do is adapt Data.Enumerator.List.concatMapAccum so that the accumulator function has the type (s -> ao -> Either (ao, [ai]) (s, [ai]) ) . The accumulator returning Right (s, [ai]) behaves as normal, while returning Left (ao, [ai]) will cause the Enumeratee to call the upstream Iterator one last time with (Chunks ai) and then yield with the (ao : xs). I just can't make it work though. Here's the guts of my attempt: step _ k EOF = yield (Continue k) EOF step s k (Chunks xs) = loop s k xs loop s k [] = continue (step s k) loop s k (x:xs) = case decoder s x of Left (extra, ai) -> k (Chunks ai) >>== checkDone (\k' -> yield () $ Chunks (extra:xs)) Right (s', ai) -> k (Chunks ai) >>== checkDoneEx (Chunks xs) (\k' -> loop s' k' xs) At this point I've tried putting a bunch of random stuff into the part to the right of (>>==) in the Left case of loop, but without any luck. Any help would be much appreciated. It seems really weird to me that none of the built-in functions for Enumeratees let you stop before the Enumerator is done. That seems like a really common thing that a person would want; in my case, I'm parsing messages out of a byte stream, so I want to stop each Enumeratee as it finishes its message, but that doesn't seem possible without dropping down to this level.

2 2

Function code generation (Template Haskell).
by Serguey Zefirov 18 Sep '11

18 Sep '11

The task is that I have some function and I need to create another function alongside with it. The second function is based on first one. As a matter of fact, I already did this with Template Haskell. TH is quite good at that task, because I can load my module in ghci and have both functions available for experiments. I just wondering, is it possible to use newly introduced ghc plugins to do something like that? Could I create new functions while inspecting defined ones? Will they be visible in ghci?

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ANN: usb-1.0, bindings-libusb-1.4.4 and usb-iteratee-0.4
by Bas van Dijk 18 Sep '11

18 Sep '11

Fellow Haskellers, I would like to announce the 1.0 release of the usb library! This library lets you to communicate with USB devices from userspace. It is implemented as a high-level wrapper around bindings-libusb[1] which is a low-level binding to the portable C library: libusb-1.0 ( http://libusb.org ). I think a 1.0 release is warranted since I have been successfully using the library in an industrial application at Sensor Sense for some time now. This release also adds the last piece of functionality that was missing from previous releases: isochronous transfers. These let you communicate with USB video or audio devices for example. A second major change is that all I/O functions, while still having a synchronous interface (they block), are now implemented asynchronously. This makes them more efficient (no busy-loops) and interruptible (just throw an asynchronous exception to the thread executing a transfer and the transfer is automatically canceled). The implementation uses the GHC event manager for event handling. If the event manager is not available, because you're either: not using GHC, building your program without -threaded or you're on Windows the implementation degrades gracefully to the synchronous implementation. Other changes: * Added writeControlExact :: DeviceHandle -> ControlAction WriteExactAction. * All I/O functions which previously returned the boolean TimedOut now return a: data Status = Completed | TimedOut. * Added the timeout constant: noTimeout :: Timeout. * Added function: maxIsoPacketSize :: EndpointDesc -> Size Which calculates the maximum packet size which a specific endpoint is capable of sending or receiving in the duration of 1 microframe. This function is mainly useful for setting up isochronous transfers. * Added some specific IOExceptions: ioException :: USBException incompleteReadException :: USBException incompleteWriteException :: USBException * Renamed System.USB.IO.Synchronous to just System.USB.IO. * Renamed System.USB.Unsafe to System.USB.Internal and exported more functions from it which are primarily needed in the usb-iteratee package. * Fixed some bugs. * Switched from darcs to git and hosted the project on github: https://github.com/basvandijk/usb/ API Docs: http://hackage.haskell.org/package/usb-1.0 Installing: $ cabal update $ cabal install usb I would like to thank John Obbele for pushing me to write the asynchronous implementation and for testing the library. Also thanks to Joris Putcuyps for testing the library on Windows. Unfortunately the library doesn't yet work on that platform due to a weird segmentation fault: http://hackage.haskell.org/trac/ghc/ticket/5254. Hopefully we will solve it in the near future. bindings-libusb =============== The usb library is based on bindings-libusb which is a low-level binding to the libusb C library. I recently took over maintenance of this package from Maurício Antunes. Maurício, thanks for creating and maintaining this package! It greatly simplified the task of writing the high-level wrapper. API Docs: http://hackage.haskell.org/package/bindings-libusb-1.4.4 usb-iteratee ============ I also released a new library: usb-iteratee which provides iteratee enumerators for the usb package. Note that this package was previously called usb-enumerator. However I'm planning to rewrite the latter to offer enumerators for the enumerator package instead. API Docs: http://hackage.haskell.org/package/usb-iteratee-0.4 Regards, Bas

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[Haskell] [ANNOUNCE] Haskdogs-0.1
by Sergey Mironov 17 Sep '11

17 Sep '11

Hi! I am pleased to announce haskdogs - project-level ctag file generator. haskdogs is a small shellscript-like tool which creates tag file for entire haskell project directory. It takes into account first-level dependencies by recursively scanning imports and adding matching packages to the final tag list. As a result, programmer can use his/her text editor supporting tags (vim, for example) to jump directly to definition of any standard or foreign function he/she uses. Note, that haskdogs calls some Unix shell commands like test or mkdir so this tool will likely fail to work on pure Windows platforms. To use it, do 0) cabal install hasktags haskdogs && mkdir -p ~/.cabal/var/haskdogs 1) cabal unpack TrickyProject-4.2 && cd TrickyProject-4.2 2) haskdogs 3) enjoy the tagfile with references to every function http://hackage.haskell.org/package/haskdogs-0.1 Sergey

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Error in Installing Data.deriveTH
by mukesh tiwari 17 Sep '11

17 Sep '11

Hello all I am trying to install Data.deriveTH . When i tried cabal install derive , i got this error. ntro@ntro-HP-dx2480-MT-NA121PA:~/Mukesh/assignment_haskell/work$ cabal install deriveResolving dependencies...<command line>: cannot satisfy -package Cabal-1.10.2.0: Cabal-1.10.2.0-072fce39d68f011c6a364057a3d15270 is unusable due to missing or recursive dependencies: containers-0.3.0.0-ee442470d8dcc9e45f31677c400c5379 (use -v for more information)cabal: Error: some packages failed to install:derive-2.5.4 depends on haskell-src-exts-1.11.1 which failed to install.haskell-src-exts-1.11.1 failed during the configure step. The exception was:ExitFailure 1 ntro@ntro-HP-dx2480-MT-NA121PA:~/Mukesh/assignment_haskell/work$ cabal install haskell-src-extsResolving dependencies...<command line>: cannot satisfy -package Cabal-1.10.2.0: Cabal-1.10.2.0-072fce39d68f011c6a364057a3d15270 is unusable due to missing or recursive dependencies: containers-0.3.0.0-ee442470d8dcc9e45f31677c400c5379 (use -v for more information)cabal: Error: some packages failed to install:haskell-src-exts-1.11.1 failed during the configure step. The exception was:ExitFailure 1 ntro@ntro-HP-dx2480-MT-NA121PA:~/Mukesh/assignment_haskell/work$ cabal install containersResolving dependencies...No packages to be installed. All the requested packages are already installed.If you want to reinstall anyway then use the --reinstall flag. I tried to resolve this issue on #haskell and i got suggestion that it was due to conflict in global and local namespace [ see here for more detail http://hpaste.org/51376 ]. One idea is i should wipe ~/.ghc and install all the libraries individually. Could some one please suggest if there is another idea to resolve this issue. Currently i have ghc-6.12.3 and installing ghc-7.0 will resolve the issue ? Thank you Mukesh Tiwari .

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Packaged my log visualization tools
by Eugene Kirpichov 17 Sep '11

17 Sep '11

Hello cafe, I've packaged my log visualization tools in binary form for several platforms. Perhaps those of you who have better things to do than struggle installing them from source will find this useful :) Here you go: http://jkff.info/presentations/two-visualization-tools.pdf Documentation http://jkff.info/software/timeplotters-0.1-1_win32.zip Windows (any architecture) http://jkff.info/software/timeplotters-0.1-1_i386.deb Debian (i386) http://jkff.info/software/timeplotters-0.1-1_amd64.deb Debian (amd64) http://jkff.info/software/timeplotters-0.1-1_i386.tar.gz *nix binaries (i386), require gtk2.0, gmp3, libc6. http://jkff.info/software/timeplotters-0.1-1_amd64.tar.gz *nix binaries (amd64), require gtk2.0, gmp3, libc6. -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

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ANNOUNCE: qrcode: QR Code encoder in pure Haskell
by Chris Yuen 17 Sep '11

17 Sep '11

Hello cafe, My first Hackage upload is a pure Haskell QR Code library ( http://hackage.haskell.org/package/qrcode-0.1) This is intended to be a full featured QR Code library with encoding and decoding and other advanced features. Currently it can only do encoding but I figured it would be nice to get some early feedback so here we go :) Cheer, Chris

2 1

pattern matching instead of prelude.head
by Michael Litchard 17 Sep '11

17 Sep '11

Someone commented on StackOverflow that pattern matching the first element of a list was preferable to head. This makes sense intuitively. Could someone articulate the reason why this is true?

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VirtuaHac - online Haskell hacathon
by Chris Smith 16 Sep '11

16 Sep '11

Overview ======== VirtuaHac is a Haskell hacathon being planned using Google+ and a Wiki. The rules will be that if you have a project you'd like to participate in, then: 1. Create a darcs or git repository. 2. Post a Hangout in Google+. 3. Add a name, brief description, and links to the preceding two items to the Wiki. This way, we hope to recreate the idea of a Hacathon, but without the travel expenses or inconvenience. What Next? ========== I'm taking a poll of availability, at https://docs.google.com/spreadsheet/viewform?formkey=dDZ3Tjh1RzVDeHdRYWhNTk… The poll will remain open for the next week, after which I'll choose a date so we can all start planning. -- Chris Smith

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ANN: numerals
by Roel van Dijk 16 Sep '11

16 Sep '11

Hello everyone, I would like to announce the release of the numerals and numerals-base packages. * Numerals The numerals package contains functions to convert numbers to number words in a number of languages. For now the package only supports cardinal numbers. Example: >>> import qualified Text.Numeral.Language.EN as EN >>> EN.uk_cardinal 123 :: Maybe String Just "one hundred and twenty-three" You can also inspect the underlying structure of a number word: >>> import Text.Numerals >>> EN.shortScaleStruct 123 :: Exp Add (Mul (Lit 1) (Lit 100)) (Add (Mul (Lit 2) (Lit 10)) (Lit 3)) Compare this structure with the number word: 1 (one) * 100 (hundred) + (and) 2 (twen) * 10 (ty) + 3 (three) The package also comes with a test suite: >>> cabal configure --enable-tests >>> cabal build >>> ./dist/build/test-numerals/test-numerals --hide-successes I recommend the "--hide-successes" option of test-framework (>=0.4) because there are many tests (3383). * Numerals-base The numerals-base package contains all the machinery upon which numerals is build. Using this package you can write conversion functions for your own language(s). It is documented, although the documentation can be improved. For now the numerals package is probably the best documentation. * Resources: Hackage: http://hackage.haskell.org/package/numerals http://hackage.haskell.org/package/numerals-base Github: http://github.com/roelvandijk/numerals http://github.com/roelvandijk/numerals-base * Help wanted Currently I support 24 languages. But I only have some experience with 4 of them. The rest is scraped together with information I found online. For most languages I can find online how to form the first 100 cardinal numbers. But after that information is sparse. You can help by checking and expanding the test suite. This is very simple because the test suite consists only of numbers combined with the expected cardinal number word. Regards, Roel van Dijk

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ANN: Webwire 0.1.0, netwire 1.2.5
by Ertugrul Soeylemez 16 Sep '11

16 Sep '11

Hello fellow Haskellers, webwire is an experimental web framework based on the functional reactive programming library netwire. It uses WAI under the hood and right now features only a subset of the very basics of what you need to write web sites. Features: * Reactive programming of web sites. * Stick together subapplications similar to Happstack. * Build web pages piece by piece using Yesod-inspired widgets. * Builtin support for "shakespearean" templates. * Builtin support for selecting output types (like HTML/JSON). * Simple Happstack-style routing functionality. * Very simple overall design. * And as always: 100% Haddock documentation coverage. Its aim is to combine all the good features of continuation-based web frameworks by hiding as much as possible of the stateless nature of HTTP. Through the netwire library it introduces some new design patterns, which appear to work amazingly well for web applications: * Powerful new design pattern for sessions: Through netwire's context-sensitive wires it becomes almost trivial to have separate subwires for every user. This way you can write your applications like you were in a dialog with the user. I'm planning to implement forms based on the same design pattern. * Feedback and choice make it easy to express complicated inter-request data dependencies. And together with webwire I have also released a new version of netwire. Changes include: * Generalized context wire transformers. * Generalized session functions. * Signal injection (reinject exhibited signals). Thanks go to: Cale Gibbard for support with AFRP, the Yesod team for lots of useful libraries. Keep the feedback coming! Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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Karatsuba Multiplication Parallel
by Burak Ekici 16 Sep '11

16 Sep '11

Dear All, I am trying to parallelize the below Karatsuba multiplication code. However, at each trial of mine the error message speaking of "incorrect indentation" is returned. I could not come up with ideas to solve the problem. I will be more than glad and appreciated, if any of you sheds light on the issue and point out the problem with its solution. Many thanks in advance, Cheers, Burak. import Control.Parallel import Control.Parallel.Strategies normalize [] = [] normalize (False : xs) = let ns = normalize xs in if ns == [] then [] else (False : ns) normalize (True : xs) = True : (normalize xs) mul [] _ = [] mul (False : xs) ys = False : (mul xs ys) mul (True : xs) ys = mul (False : xs) ys `add` ys mulk3 [] _ = [] mulk3 _ [] = [] mulk3 xs ys = (normalize (mulk3 xs0 ys0)) `add` (replicate l False ++ (((mulk3 (add xs0 xs1) (add ys0 ys1)) `sub` (normalize (mulk3 xs0 ys0)) `sub` (normalize (mulk3 xs1 ys1))) `add` (replicate l False ++ (normalize (mulk3 xs1 ys1))))) where l = (min (length xs) (length ys)) `div` 2 (xs0, xs1) = splitAt l xs (ys0, ys1) = splitAt l ys if l > 32 then (normalize (mulk3 xs0 ys0)) `par` (normalize (mulk3 xs1 ys1)) `par` ((mulk3 (add xs0 xs1) (add ys0 ys1)) `sub` (normalize (mulk3 xs0 ys0)) `sub` (normalize (mulk3 xs1 ys1))) else mul xs ys

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darcs checkin history?? forgot ....
by Vasili I. Galchin 16 Sep '11

16 Sep '11

Hello, If I have a URL for a darcs repository, how can I get a listing of activity ... mainly "checkin" history .... e.g. name, date timestamp? Thanks, Vasili

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Re: [Haskell-cafe] [Haskell] [ANNOUNCE] Haskdogs-0.1
by Ivan Lazar Miljenovic 16 Sep '11

16 Sep '11

Re-cc'ing -cafe: On 14 September 2011 14:29, yi huang <yi.codeplayer(a)gmail.com> wrote: > On Wed, Sep 14, 2011 at 11:32 AM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: >> >> On 14 September 2011 13:27, yi huang <yi.codeplayer(a)gmail.com> wrote: >> > On Wed, Sep 14, 2011 at 10:18 AM, Ivan Lazar Miljenovic >> > <ivan.miljenovic(a)gmail.com> wrote: >> >> >> >> On 14 September 2011 11:24, yi huang <yi.codeplayer(a)gmail.com> wrote: >> >> > Cabal compains about "Unknown build tool hasktags". >> >> > It seems not necessary to set "Build-tools: hasktags" in cabal file? >> >> >> >> cabal-install isn't capable of automatically building and installing >> >> build-tools for you. So to install haskdogs, you need to do "cabal >> >> install hasktags && cabal install haskdogs". >> > >> > I have installed hasktags, and .cabal/bin is in my PATH, i can run >> > hasktags >> > directly from shell. >> > What else did i miss? >> >> How did you specify your PATH? You can't use ~/.cabal/bin, you need >> either $HOME/.cabal/bin or the fully expanded path. > > It is $HOME/.cabal/bin , and `which hasktags' can find it without problem. > Cabal 1.10.2, ghc 7.0.4, i'm trying to look into cabal source to find the > problem. Actually... looks like you're right. I can't build it either, he appears to have hard-coded some paths in and it appears that you need some kind of magic to register a program as a build tool (that's what the error is from: hasktags isn't a registered build-tool). -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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Categorized Weaknesses from the State of Haskell 2011 Survey
by Nick Knowlson 15 Sep '11

15 Sep '11

Hello all, I did a followup analysis of the free-form responses to "What is Haskell's most glaring weakness / blind spot / problem" in the State of Haskell 2011 Survey. The article is up at: http://nickknowlson.com/blog/2011/09/12/haskell-survey-categorized-weakness… I think it has a lot of interesting information in it - I hope some others will find it useful now too. Cheers, Nick

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Error in cabal install of monad-par?
by Rishiyur Nikhil 15 Sep '11

15 Sep '11

I'm following the instructions on the CUFP "T5 Parallel Programming in Haskell" web page for preparing for the tutorial, where it asks that I should: 'cabal install monad-par'. I'm doing this on a Mac, Snow Leopard 10.6.8, after installing Haskell Platform. I have Xcode 3.2.4 installed. I get the following error; please let me know how I should fix it (can reply to me personally instead of the list, at 'nikhil at acm dot org'. Thanks. Nikhil $ cabal install monad-par Resolving dependencies... Configuring monad-par-0.1.0.1... Preprocessing library monad-par-0.1.0.1... Building monad-par-0.1.0.1... Control/Monad/Par/Internal.hs:4:15-71: unknown flag in {-# OPTIONS #-} pragma: -fno-warn-unused-do-bind cabal: Error: some packages failed to install: monad-par-0.1.0.1 failed during the building phase. The exception was: ExitFailure 1

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Tupling functions
by Richard O'Keefe 15 Sep '11

15 Sep '11

I would like to have tuple (f1,f2) x = (f1 x, f2 x) tuple (f1,f2,f3) x = (f1 x, f2 x, f3 x) tuple (f1,f2,f3,f4) x = (f1 x, f2 x, f3 x, f4 x) ... I'm aware of Control.Arrow and the &&& combinator, and I can use that instead, but f1 &&& f2 &&& f3 doesn't have _exactly_ the type I want. What should I do?

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efficient chop
by Kazu Yamamoto 15 Sep '11

15 Sep '11

Hello Cafe, I would like to have an efficient implementation of the chop function. As you guess, the chop function drops spaces in the tail of a list. chop " foo bar baz " -> " foo bar baz" A naive implementation is as follows: chopReverse :: String -> String chopReverse = reverse . dropWhile isSpace . reverse But this is not elegant. foldr version is as follows: chopFoldr :: String -> String chopFoldr = foldr f [] where f c [] | isSpace c = [] | otherwise = c:[] f c cs = c:cs But this code is slower than chopReverse in some cases. Are there any more efficient implementations of chop? Any suggestions? --Kazu

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static analysis (call graph) tools?
by Johannes Waldmann 15 Sep '11

15 Sep '11

Dear Cafe, what tools are there for static analysis of Haskell programs? I mean simple things like the call graph (who is calling whom). Which are, of course, not that simple because of higher order functions. Do leksah/eclipsefp(/ghc api) have something like "show all uses of an identifier" (eclipse: "open call hierarchy") (with correct handling of scoping and modules)? Thanks - Johannes.

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Haskell Weekly News: Issue 199
by Daniel Santa Cruz 15 Sep '11

15 Sep '11

Welcome to issue 199 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of September 4 to 10, 2011. Announcements Johannes Waldmann open the invitation to the 6th Haskell in Leipzig workshop, on October 7, 2011. It "will present an absolutely thrilling mixture of tutorials and talks, with special enphasis on parallel programming." [1] http://goo.gl/u0PwF New and Updated Projects * Hs2lib (Phyx; v-0.5.5) A preprocesor and library which allow you to create dynamic libs from arbitrary annotated Haskell programs with one click. It also allows you to use the generated lib in C, C++, and C# just by including the generated header files. [2] http://goo.gl/xCSXc * Netwire (Ertugrul Soeylemez; 1.2.0) Lots of new features! [3] http://goo.gl/VCwb1 * network-address (Sebastian Nowicki; 0.2.0) Provides data structures and textual representation of network addresses (IPv4, IPv6, subnets). [4] http://goo.gl/DBRI6 * Webrexp (Vincent Berthoux; 1.1) A web scraping command line utility. [5] http://goo.gl/OlovQ * eddie (Mike Meyer; 0.5) Is a tool for applying haskell filters to text files via the unix command line. [6] http://goo.gl/NPc0b * cabal-ghci (Etienne Laurin; 0.1) Package to ease the development of projects using cabal. [7] http://goo.gl/fiDKZ Quotes of the Week * gosu: Type parameters are covariant. This is not sound, and that does not matter. * turtlesalltheway: if haskell is so great why cant it improve itself * mm_freak: bosses are generally quite strong, static and lazy * cmccann: newtype Natural = N { denature :: Integer } Top Reddit Stories * Constraint Kinds for GHC Domain: blog.omega-prime.co.uk, Score: 115, Comments: 12 On Reddit: [8] http://goo.gl/bCXgf Original: [9] http://goo.gl/7aWzn * Yesod :: The Limitations of Haskell Domain: yesodweb.com, Score: 108, Comments: 42 On Reddit: [10] http://goo.gl/5q7wW Original: [11] http://goo.gl/gisIh * Frege: haskell like language on JVM (tries to adhere to haskell 2010 where possible) Domain: code.google.com, Score: 58, Comments: 58 On Reddit: [12] http://goo.gl/6KWEg Original: [13] http://goo.gl/56AkX * Sharing in Haskell – How the let and lambda constructs give a precise way to control sharing Domain: neilmitchell.blogspot.com, Score: 34, Comments: 18 On Reddit: [14] http://goo.gl/Uf1vq Original: [15] http://goo.gl/4Hmfu * Let's play a game : How to implement functions from their type signatures Domain: blog.ezyang.com, Score: 24, Comments: 13 On Reddit: [16] http://goo.gl/T2FiD Original: [17] http://goo.gl/SmbYO * Impredicativity + injectivity + type case analysis = inconsistency (Russell paradox) :: Oleg Domain: okmij.org, Score: 23, Comments: 10 On Reddit: [18] http://goo.gl/zoThI Original: [19] http://goo.gl/jFr5U * Functional Pearls Domain: haskell.org, Score: 23, Comments: 1 On Reddit: [20] http://goo.gl/RVyng Original: [21] http://goo.gl/1A7t0 * An EventSource broker written in Haskell Domain: mathias-biilmann.net, Score: 22, Comments: 0 On Reddit: [22] http://goo.gl/7yywu Original: [23] http://goo.gl/Y5mGj * Haskell For Kids: Week 4 Domain: cdsmith.wordpress.com, Score: 22, Comments: 2 On Reddit: [24] http://goo.gl/KwlqD Original: [25] http://goo.gl/xlNh2 * apfelmus - Vault - a persistent store for values of arbitrary types Domain: apfelmus.nfshost.com, Score: 19, Comments: 2 On Reddit: [26] http://goo.gl/VAE4n Original: [27] http://goo.gl/vvQ7A * Tau is available in Haskell, you can safely avoid Pi Domain: hackage.haskell.org, Score: 19, Comments: 26 On Reddit: [28] http://goo.gl/u5GN8 Original: [29] http://goo.gl/VnrMh * Zipper from any Traversable :: Oleg Domain: okmij.org, Score: 18, Comments: 2 On Reddit: [30] http://goo.gl/xi4ZF Original: [31] http://goo.gl/nqZ3T Top StackOverflow Questions * More on generic Scala functions votes: 20, answers: 4 Read on SO: [32] http://goo.gl/DGH14 * Why is a “type class” called “type class”? votes: 20, answers: 2 Read on SO: [33] http://goo.gl/YbVXX * Is there a Haskell idiom for updating a nested data structure? votes: 14, answers: 2 Read on SO: [34] http://goo.gl/jKEjv * How to tell if a list is infinite? votes: 14, answers: 4 Read on SO: [35] http://goo.gl/fc3e6 * Select random element from a set, faster than linear time (Haskell) votes: 9, answers: 5 Read on SO: [36] http://goo.gl/IRJf3 * GHC not optimising modules other than the main module votes: 9, answers: 0 Read on SO: [37] http://goo.gl/8Ephm * A chess board representation in Haskell votes: 8, answers: 4 Read on SO: [38] http://goo.gl/iSM7d * How to cap memory usage of Haskell threads votes: 7, answers: 2 Read on SO: [39] http://goo.gl/dvLnE * Is this Haskell type inference in action, or something else? votes: 7, answers: 2 Read on SO: [40] http://goo.gl/hTaK7 * Assymmetry in the bind function votes: 6, answers: 7 Read on SO: [41] http://goo.gl/KqMTn About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92287 2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92182 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92225 4. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18916 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18929 6. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18930 7. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92279 8. http://blog.omega-prime.co.uk/?p=127 9. http://www.reddit.com/r/haskell/comments/kbf14/constraint_kinds_for_ghc/ 10. http://www.yesodweb.com/blog/2011/09/limitations-of-haskell 11. http://www.reddit.com/r/haskell/comments/k4lc4/yesod_the_limitations_of_has… 12. http://code.google.com/p/frege/ 13. http://www.reddit.com/r/haskell/comments/kadx6/frege_haskell_like_language_… 14. http://neilmitchell.blogspot.com/2011/09/sharing-in-haskell.html 15. http://www.reddit.com/r/haskell/comments/k4bq9/sharing_in_haskell_how_the_l… 16. http://blog.ezyang.com/2011/09/lets-play-a-game/ 17. http://www.reddit.com/r/haskell/comments/k5okh/lets_play_a_game_how_to_impl… 18. http://okmij.org/ftp/Haskell/impredicativity-bites.html 19. http://www.reddit.com/r/haskell/comments/k5bdb/impredicativity_injectivity_… 20. http://www.haskell.org/haskellwiki/Research_papers/Functional_pearls 21. http://www.reddit.com/r/haskell/comments/kb3w5/functional_pearls/ 22. http://mathias-biilmann.net/posts/2011/9/a-haskell-eventsource-broker 23. http://www.reddit.com/r/haskell/comments/k6fva/an_eventsource_broker_writte… 24. http://cdsmith.wordpress.com/2011/09/10/haskell-for-kids-week-4/ 25. http://www.reddit.com/r/haskell/comments/kbqn0/haskell_for_kids_week_4/ 26. http://apfelmus.nfshost.com/blog/2011/09/04-vault.html 27. http://www.reddit.com/r/haskell/comments/k4l6c/apfelmus_vault_a_persistent_… 28. http://hackage.haskell.org/package/tau 29. http://www.reddit.com/r/haskell/comments/kazfn/tau_is_available_in_haskell_… 30. http://okmij.org/ftp/continuations/zipper.html#traversable 31. http://www.reddit.com/r/haskell/comments/k5bci/zipper_from_any_traversable_… 32. http://stackoverflow.com/questions/7337582/more-on-generic-scala-functions 33. http://stackoverflow.com/questions/7360024/why-is-a-type-class-called-type-… 34. http://stackoverflow.com/questions/7365425/is-there-a-haskell-idiom-for-upd… 35. http://stackoverflow.com/questions/7371730/how-to-tell-if-a-list-is-infinite 36. http://stackoverflow.com/questions/7349080/select-random-element-from-a-set… 37. http://stackoverflow.com/questions/7367070/ghc-not-optimising-modules-other… 38. http://stackoverflow.com/questions/7309554/a-chess-board-representation-in-… 39. http://stackoverflow.com/questions/7297654/how-to-cap-memory-usage-of-haske… 40. http://stackoverflow.com/questions/7342222/is-this-haskell-type-inference-i… 41. http://stackoverflow.com/questions/7319424/assymmetry-in-the-bind-function

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