- Haskell-Cafe - Haskell.org

ANNOUNCE: smallcheck-0.6; test-framework-smallcheck-0.1
by Roman Cheplyaka 11 Dec '11

11 Dec '11

I'm pleased to announce a new release of SmallCheck. The highlights for this release are: * Default Generic implementation of Serial instance, contributed by Bas van Dijk This means that you don't need to write instances by hand for your types to generate test values for them. See [1] for the details. [1]: http://hackage.haskell.org/packages/archive/smallcheck/0.6/doc/html/Test-Sm… * Revised, organised into modules and documented API * Integration with test-framework, through test-framework-smallcheck package It allows to organize SmallCheck properties into a test suite (possibly together with HUnit or QuickCheck tests), apply timeouts, get nice statistics etc. Thanks to Max Bolingbroke for cooperation on this front. Please refer to the README for more information about SmallCheck: https://github.com/feuerbach/smallcheck/blob/master/README.md Hackage links: http://hackage.haskell.org/package/smallcheck-0.6 http://hackage.haskell.org/package/test-framework-smallcheck-0.1 -- Roman I. Cheplyaka :: http://ro-che.info/

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Sharing a room for the CRA-W/CDC/SIGPLAN Mentoring Workshop at POPL?
by Joachim Breitner 11 Dec '11

11 Dec '11

Hi, I will attend the CRA-W/CDC/SIGPLAN Mentoring Workshop at POPL next year, and will have to share a room with another attendee. As we can give preferences, I was wondering if another Haskeller might be in the same position and interested in sharing a room. Greetings, Joachim -- Joachim "nomeata" Breitner mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/

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10th Ghent Functional Programming Group Meeting on Thursday, December 15, 2011 at 19h30
by Jasper Van der Jeugt 11 Dec '11

11 Dec '11

Dear All, We would like to remind you of the 10th Ghent Functional Programming Group (GhentFPG) meeting, which will take place this Thursday, December 15, 2011, at 19h30 in the Technicum building of Ghent University (Sint-Pietersnieuwstraat 41, 9000 Gent). This meeting, we will focus on tackling some interesting problems with the elegance of functional programming. We will try to post the problems to this mailing list at least two days in advance. As with the previous meeting, the meeting room is still unreachable through the regular building entrance because of construction works. Hence, attendees need to take the alternative side entrance. This entrance can be found on the right side (as seen from the street) of the building -- it will remain open until 20:00. If you walk up to the Technicum building and go right at the bicycle stands, you should see “Ingang Blok 1 & Blok 2” indicated. Follow this, and you’ll be able to get inside, at which point you’ll see arrows pointing to the meeting room. For safety measures the blue doors will be locked, so if you arrive after 19:30, please give us a call at +32 (0) 9 264 3370, so we can come and open the doors for you. P.S. we would also like to remind you that you are all certainly welcome at the talk about "Real-World Functional Programming @ Incubaid", organized by Tom Schrijvers for his course on Functional & Logic Programming at Ghent University. For more details see [1]. [1]: https://groups.google.com/d/topic/ghent-fpg/csUnMX08WKc/discussion Hope to see you then! The GhentFPG Organizing Committee.

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Hardware description in Haskell.
by Serguey Zefirov 11 Dec '11

11 Dec '11

I would like to introduce my over-than-two years long project, HHDL: http://thesz.mskhug.ru/svn/hhdl/hackage/hhdl/ (I prefer to pronounce it as a ha-ha-dee-el, this way it is more fun) It allows one to create digital hardware description in Haskell and then generate VHDL code (Verilog is on the way). Okay, it would allow one to do all that some day. I hope it will come sooner than later. I try to make all wires as typed as I can and to support algebraic types with patetrn matching. I wrote a simple example to demonstrate some of those facilities: http://thesz.mskhug.ru/svn/hhdl/hackage/hhdl/src/Hardware/HHDL/Examples/Run… This is a simple accumulator that accepts a Maybe Word8 input. The resulting VHDL is very wordy, but looks superficially correct. I wrote two posts about HHDL: http://thesz.livejournal.com/1284055.html - slightly outdated as HHDL now generates VHDL that typechecks and allows one to name inputs and outputs http://thesz.livejournal.com/1284541.html - motivation behind HHDL There is no package for Hackage, because I do not feel HHDL is worth it right now. For example, I tested it on ghc 6.12.1, not later versions, the library code is messy. But HHDL is good enough for some scrutiny and critique by Haskell users who is into hardware description.

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[ANNOUNCEMENT] xmobar 0.14
by Jose A. Ortega Ruiz 11 Dec '11

11 Dec '11

I'm happy to announce the release of xmobar 0.14. Xmobar is a text-based, minimalistic status bar for linuxy systems, written in Haskell. See http://projects.haskell.org/xmobar for details. Many, many thanks to the many, many contributors, and apologies for taking so long to put their code and fixes under a new release. In this episode: _New features_ - New brightness monitor, courtesy of Martin Perner. - New DateZone plugin, for configurable timezone and localized datetimes, also by Martin. - New keyboard layout monitor (Kbd). Yes, by Martin. - Rewrite of the event handling ([issue 53], [issue 57]), you guessed it. - Cpu monitor now also reports `iowait` field ([issue 55]). - Battery monitor: the full charge file is now settable in the monitor arguments (olpc systems use `charge_full_design`; see [issue 62]). _Bug fixes_ - [issue 45]: Fix for crashes with AC status changes in battery monitor. - [issue 48]: The <quality> field of Wireless behaves like a percentage. - [issue 50]/[issue 61]: `MPD` monitor now works with libmpd 0.6. - [issue 60]: Fixes for crashes on power resume for battery monitor. - Template sections without fields are now correctly displayed. - Catch errors when reading battery status (Ben Boeckel). - Compilation issues with ghc 7.x (Sergei Trofimovich). - Fixes for CoreTemp monitor in new kernels (Norbert Zeh). - Fix for pulseaudio problems in volume monitor (Martin Perner). - Fix for parsing errors when a `Run` entry ended in an array (Martin). - Fixed compilation in OpenBSD (Ivo van der Sangen). [issue 45]: http://code.google.com/p/xmobar/issues/detail?id=45 [issue 48]: http://code.google.com/p/xmobar/issues/detail?id=48 [issue 50]: http://code.google.com/p/xmobar/issues/detail?id=50 [issue 53]: http://code.google.com/p/xmobar/issues/detail?id=53 [issue 55]: http://code.google.com/p/xmobar/issues/detail?id=55 [issue 57]: http://code.google.com/p/xmobar/issues/detail?id=57 [issue 60]: http://code.google.com/p/xmobar/issues/detail?id=60 [issue 61]: http://code.google.com/p/xmobar/issues/detail?id=61 [issue 62]: http://code.google.com/p/xmobar/issues/detail?id=62 Cheers, jao

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web-routes-quasi: Generating a route type
by Ertugrul Söylemez 11 Dec '11

11 Dec '11

Hello there, I'm trying to use the web-routes-quasi package outside of Yesod. Is there any documentation on how to use TH to generate a route type just like Yesod does? Or is that a Yesod-specific feature? I don't need the actual automatic dispatch or anything, just a type to work with. If it's not possible, I will just go ahead and (ab-) use the constructor strings. Greets, Ertugrul -- nightmare = unsafePerformIO (getWrongWife >>= sex) http://ertes.de/

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Munich Haskell Meeting
by Heinrich Hördegen 10 Dec '11

10 Dec '11

Dear all, the doodle poll for the next Haskell get-together indicates, that we should meet on Tuesday, 13 Dec 2011, 19h30 at Cafe Puck: http://www.doodle.com/x6x4sgnemc35myq3 I will reserve tables. For all those who cannot join, sorry, but we hope to meet you next year. Check out the dates: http://www.haskell-munich.de/dates So, let's meet at Tuesday for the last time this year. Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Hexpat: Lazy I/O problem with huge input files
by Aleksandar Dimitrov 10 Dec '11

10 Dec '11

Hello Haskell Cafe, I really hope this is the right list for this sort of question. I've bugged the folks in #haskell, they say go here, so I'm turning to you. I want to use Hexpat to read in some humongous XML files (linguistic corpora,) since it's the only Haskell XML library (I could find) that takes ByteStrings as input. I stumbled on a problem when using one of the examples from the docs of Text.XML.Expat.Tree. The "cookbook recipe" there suggests *first* processing the data, and only then looking into the parser error to see if there has been an error. I understand this should prevent the parse tree from being fully evaluated before use. Unfortunately, that is not what happens on my system (ghc 6.12.1, if that's of importance.) This is the code from the docs, that I modified to read files: > import Text.XML.Expat.Tree > import System.Environment (getArgs) > import Control.Monad (liftM) > import qualified Data.ByteString.Lazy as C >· > -- This is the recommended way to handle errors in lazy parses > main = do > f <- liftM head getArgs >>= C.readFile > let (tree, mError) = parse defaultParseOptions f > print (tree :: UNode String) >· > -- Note: We check the error _after_ we have finished our processing > -- on the tree. > case mError of > Just err -> putStrLn $ "It failed : "++show err > Nothing -> putStrLn "Success!" Given a 42M test file, an invocation like this: % ghc --make -O2 Hexpat.hs % ./Hexpat input.xml > dump.xml will gobble up some 2Gigs of RAM (at least. I usually kill it before it starts thrashing the swap space, since that almost crashes my entire machine.) If I remove the last 3 lines: > import Text.XML.Expat.Tree > import System.Environment (getArgs) > import Control.Monad (liftM) > import qualified Data.ByteString.Lazy as C > > main = do > f <- liftM head getArgs >>= C.readFile > let (tree, mError) = parse defaultParseOptions f > print (tree :: UNode String) the same invocation and input file barely uses a megabyte or two of RAM and finishes really quickly. Why is that? Is this a mistake in the Hexpat docs, or am I doing something wrong? Lazy IO has always been a little bit of a mystery to me, and just when I thought I had it... Thanks for any help on the matter! Aleks

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Beginning Data.Lens tutorial
by Henry Laxen 10 Dec '11

10 Dec '11

Dear Group, If you haven't used lenses before, (as I hadn't until recently) you may find this helpful: http://www.nadineloveshenry.com/haskell/lensExamples.html Best wishes, Henry Laxen

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Alternative STM implementation
by Daniel Waterworth 10 Dec '11

10 Dec '11

Hi, This morning I have written an STM implementation as a learning exercise. I thought I'd share it here to get some critique and because it might be useful to others (consider it as being in the public domain). I haven't tested it thoroughly, so there may be edge cases that haven't been thought through. It should be a drop-in replacement (so long as you only use TVars), if anyone has any STM benchmarks already made, I'd love to see how it compares. Here it is: https://gist.github.com/1454995 Thanks, Daniel

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Haskell functions caller-callee details
by Shakthi Kannan 10 Dec '11

10 Dec '11

Hi, Given a Haskell package is there a way I can get each functions' caller-callee details? Are there any existing tools/libraries that can help me get this data from the source? Appreciate any inputs in this regard. Thanks! SK -- Shakthi Kannan http://www.shakthimaan.com

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Cabal issue
by Kevin Jardine 10 Dec '11

10 Dec '11

I understand that this may have been addressed before on this list in some form, so I'll be brief: Had problem with deprecated package, was told my only option was to wipe my Haskell install and start over. Is this true and if so, doesn't this mean that Cabal (or the package management system that it is a part of) is broken? Details here: https://plus.google.com/u/0/111705054912446689620/posts/V1186HGWEap Kevin

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ANNOUNCE: Workflow-0.5.8.0
by Alberto G. Corona 09 Dec '11

09 Dec '11

This is A new version of the package workflow. I probably will change the name of this package since it is too generic. A workflow can be seen as a persistent thread that executes a monadic computation. Therefore, it can be used in very time consuming computations such are CPU intensive calculations with intermediate results or with procedures that are most of the time waiting for the response of a process or an user, that are prone to comunication failures, timeouts or shutdowns. Workflow has a operation, called "step" that lift the monadic computation to the Workflow monad. This bring services of transparent state loogging, so that the computation can be restarted at the point of stop/failure. Additionally , the package has persistent queues, persistent data collections, and persistent timeouts (whit which the workflow can wait for days, months or even years, more than the average time between failures). This is important for programming office workflow or in election processes where the user has a limited time to decide/vote. This version has many improvements: it admits Data.Binary serialization for logging (besides RefSerialize of previous versions). . It also has an EDSL of high level monadic combinators that represent workflow patterns. For example, split, merge, synchronization, votation etc. There are examples in the online documentation and some demos in the package. My motivation for developping Workflow is to use it in a project for electronic democracy in the Web. If anyone is interested in the package Workflow and/or electronic democracy, I will be happy to talk with him. Hope to be useful Alberto.

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ANNOUNCE: HaTeX 3.1.0 (and HaTeX-meta 1.1.0)
by Daniel Díaz Casanueva 09 Dec '11

09 Dec '11

Hello Cafe! Today I released to Hackage a new version of the HaTeX package ( http://hackage.haskell.org/package/HaTeX-3.1.0 ). If you don't know HaTeX, it is a combinator library of the LaTeX syntax. Visit the homepage for more information: http://dhelta.net/hprojects/HaTeX Highlights: + Added warnings (See Text.LaTeX.Base.Warnings). Still very experimental. + Added an "Examples" directory, with a simple example inside to get started. + Num instance for LaTeX and LaTeXT. + New package implemented "AMSThm" (See Text.LaTeX.Packages.AMSThm). See the ReleaseNotes in the source tarball for more details in release changes. With it, I released an update of HaTeX-meta (version 1.1.0), which produces part of the HaTeX code. An important change here is the addition of the HATEX pragma (explained in http://deltadiaz.blogspot.com/2011/11/hatex-pragma.html ). If you need something more, feel free to contact me or send me a patch.

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Does anyone maintain trac.haskell.org?
by Justin Bailey 09 Dec '11

09 Dec '11

The community Trac hosting server isn't sending email, which Trac requires. I've submitted several tickets to support(a)community.haskell.org but gotten no response. Does anyone maintain that server anymore? Justin

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CfP: Only one week left for submitting abstracts to TAP 2012 (International Conference on Test and Proofs
by Achim D. Brucker 09 Dec '11

09 Dec '11

(Apologies for duplicates) ************************************************* **** Less than one week until the deadline *** **** for submitting abstract to TAP 2012 *** ************************************************* CALL FOR PAPERS Full and short Research Paper, Industrial Expierence Papers, Tool Papers Abstract submission: Dec 14, 2011, Paper submission Dec 21, 2012 6th INTERNATIONAL CONFERENCE ON TEST AND PROOFS (TAP 2012) http://lifc.univ-fcomte.fr/tap2012/ May 31 - June 1, 2012, Prague, Czech Republic Part of the TOOLS Federated Conferences 2012 http://tools2012.fit.cvut.cz/ The TAP conference is devoted to the convergence of proofs and tests, to the application of techniques from both sides and their combination for the advancement of software quality. Test and Proof seem to be contradictory techniques: if you have proved your program to be correct, it is fruitless to comb it for bugs; and if you are testing it, that is surely a sign that you have given up on any hope to prove its correctness. Accordingly, proofs and tests have, since the onset of software engineering research, been pursued by distinct communities. However, the development of both approaches lead to the discovery of common issues and to the realization that each may need the other. The emergence of model checking has been one of the first signs that contradiction may yield to complementarity. Further evidence give test data generation techniques from models or programs which boil down to constraint resolution techniques for relatively large formula; the advent of powerful SMT solvers have therefore powered new testing techniques. Finally, since formal, proof-based verification is costly, testing invariants and background theories can be helpful to detect errors early and to improve cost effectivity. Summing up, in the past few years an increasing number of research efforts have encountered the need for combining proofs and tests, dropping earlier dogmatic views of incompatibility and taking instead the best of what each of these software engineering domains has to offer. The TAP conference aims to bring together researchers and practitioners working in the converging fields of testing and proving, and will offer a generous allocation of papers, panels and informal discussions. Topics of interest cover theory definitions, tool constructions and experimentations and include (other topics related to TAP are welcome): - Transfer of concepts from testing to proving (e.g., coverage criteria) and from proving to testing - Program proving with the aid of testing techniques - New problematics in automated reasoning emerging from specificities of test generation - Verification and testing techniques combining proofs and tests - Generation of test data, oracles, or preambles by deductive techniques such as: theorem proving, model checking, symbolic execution, constraint logic programming - Model-based testing and verification - Generation of specifications by deduction - Automatic bug finding - Debugging of programs combining static and dynamic analysis - Formal frameworks - Tool descriptions and experience reports - Case studies combining tests and proofs - Applying combination of test and proof techniques to new application domains such as validating security procotols or vulnerability detection of programs Important Dates: ================ Abstract submission: December 14, 2011 Paper submission: December 21, 2011 Notification: March 2, 2012 Camera ready version: March 19, 2012 TAP conference: May 31 - June 1, 2012 (to be confirmed) TOOLS conferences (TOOLS, ICMT, SC, TAP): May 29 - June 01, 2012 Conference Chairs: Bertrand Meyer Program Chairs: Achim D. Brucker and Jacques Julliand Program Committee (to be extended): =================================== Nazareno Aguirre, Bernhard K. Aichernig, Paul Ammann, Dirk Beyer, Nikolaj Bjorner, Robert Clarisó, Marco Comini, Catherine Dubois, Gordon Fraser, Angelo Gargantini, Alain Giorgetti, Patrice Godefroid, Martin Gogolla, Arnaud Gotlieb, Reiner Hähnle, Bart Jacobs, Thierry Jéron, Gregory Kapfhammer, Nikolai Kosmatov, Victor Kuliamin, Karl Meinke, Jeff Offutt, Holger Schlingloff, T.H. Tse, Margus Veanes, Luca Viganò, Burkhart Wolff, Fatiha Zaidi Submission: =========== Please submit your papers via http://lifc.univ-fcomte.fr/tap2012/. TAP 2012 will accept two types of papers: - Research papers: full papers with at most 16 pages in LNCS format (pdf), which have to be original, unpublished and not submitted elsewhere. - Short contributions: work in progress, (industrial) experience reports or tool demonstrations, position statements; an extended abstract with at most 6 pages in LNCS format (pdf) is expected. Accepted papers will be published in the Springer LNCS series and will be available at the conference. The contents of previous TAP proceedings is available at: http://www.informatik.uni-trier.de/~ley/db/conf/tap/ -- Dr. Achim D. Brucker, SAP Research, Vincenz-Priessnitz-Str. 1, D-76131 Karlsruhe Phone: +49 6227 7-52595, Fax: +49-6227 78-50502, http://www.brucker.ch

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[ANNOUNCE] cereal-0.3.5.0
by Trevor Elliott 09 Dec '11

09 Dec '11

Hi Everyone, I'm pleased to announce the release of cereal version 0.3.5.0! New to this release is support for default, generic implementations of the get and put methods of the Serialize class, when support is available. This functionality comes to you courtesy of Bas van Dijk. Happy Hacking! --trevor

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More liberal than liberal type synonyms
by Dan Doel 08 Dec '11

08 Dec '11

Greetings, In the process of working on a Haskell-alike language recently, Ed Kmett and I realized that we had (without really thinking about it) implemented type synonyms that are a bit more liberal than GHC's. With LiberalTypeSynonyms enabled, GHC allows: type Foo a b = b -> a type Bar f = f String Int baz :: Bar Foo baz = show because Bar expands to saturate Foo. However, we had also implemented the following, which fails in GHC: type Foo a b = b -> a type Bar f = f (Foo Int) (Foo Int) type Baz f g = f Int -> g Int quux :: Bar Baz quux = id That is: type synonyms are allowed to be partially applied within other type synonyms, as long as similar transitive saturation guarantees are met during their use. I don't know how useful it is, but I was curious if anyone can see anything wrong with allowing this (it seems okay to me after a little thought), and thought I'd float the idea out to the GHC developers, in case they're interested in picking it up. -- Dan

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Converting string to System.Time.ClockTime
by dokondr 08 Dec '11

08 Dec '11

Hi, What would be the simplest way to convert strings like "Wed, 07 Dec 2011 10:09:21 +0000" to System.Time.ClockTime ? Thanks!

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Disjunctive patterns
by Asger Feldthaus 08 Dec '11

08 Dec '11

Haskell doesn't seem to support disjunctive patterns, and I'm having a difficult time writing good Haskell code in situations that would otherwise call for that type of pattern. Suppose for an example I have this data type: data T = Foo Int | Bar Int | Baz In OCaml I can write something like: (* foo : T -> T -> int *) fun foo x y = match (x,y) with | (Foo a | Bar a, Foo b | Bar b) -> a + b | (Baz, Foo a) | (Bar a, Baz) -> -a | (Baz, Bar a) | (Foo a, Baz) -> a | _ -> 0 In Haskell I can't find any equivalent to the disjunctive pattern. If expanded naively, my Haskell version would look like this: foo :: T -> T -> Int foo x y = case (x,y) of (Foo a, Foo b) -> a + b (Foo a, Bar b) -> a + b (Bar a, Foo b) -> a + b (Bar a, Bar b) -> a + b (Baz, Foo a) -> -a (Bar a, Baz) -> -a (Baz, Bar a) -> a (Foo a, Baz) -> a _ -> 0 While my example is still managable in size, this quickly goes out of hand in practice. I've tried using pattern guards but with limited success. For example: foo2 :: T -> T -> Int foo2 x y = case (x,y) of (x,y) | Just a <- open x, Just b <- open y -> a+b (Baz, Foo a) -> -a (Bar a, Baz) -> -a (Baz, Bar a) -> a (Foo a, Baz) -> a _ -> 0 where open (Foo x) = Just x open (Bar x) = Just x open Baz = Nothing I admit it doesn't look that bad in my crafted example, but this approach doesn't seem to well work for me in practice. In any case, it's still far more verbose than the disjunctive pattern version. Nesting the case expressions instead of tuple-matching can reduce some code duplication, but in general it becomes really verbose, and it is easy to make mistakes when you have partially overlapped patterns in the disjunctive-pattern version. Here's the example with nested cases: foo3 :: T -> T -> Int foo3 x y = case x of Foo a -> case y of Foo b -> a+b Bar b -> a+b Baz -> a Bar a -> case y of Foo b -> a+b Bar b -> a+b Baz -> -a Baz -> case y of Foo b -> -b Bar b -> b Baz -> 0 What do people do in this situation - is there a good trick I've overlooked? And is there some reason why Haskell does not support disjunctive patterns? Thanks, Asger

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Haskell Weekly News: Issue 210
by Daniel Santa Cruz 08 Dec '11

08 Dec '11

Welcome to issue 210 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of November 27 to December 3, 2011. You can find the HTML version at: http://contemplatecode.blogspot.com/2011/12/haskell-weekly-news-issue-210.h… Announcements Heinrich Hordegen announced a tentative 2012 meeting schedule for Munich Haskell group. [1] http://goo.gl/JrnP6 New and Updated Projects * data-timeout (Mikhail Vorozhtsov) Allows one to specify time units for timeouts and convert between them. [2] http://goo.gl/fbfGM * Netwire (Ertugrul Soylemez; 3.0.0) Major API change. [3] http://goo.gl/8hPwS * monad-control (Bas van Dijk; 0.3) New and improved API. [4] http://goo.gl/so3s9 Quotes of the Week * Jafet: They're not nasty; their niceness is just distributed over more people * copumpkin: U NEED MOANAD * xplat: i have a feeling that trying to write an interesting dependently-typed program in Shen at any time in the near future would be like trying to host a holiday dinner starting with an empty lot, 2x4s, a stack of window panes, some cables and wiring boxes, sheets of drywall, disconnected appliances, roof shingles, rolls of insulation and bags of concrete * Axman6: {-# PRAGMA ThisShitNeedsMoarFast #-} Top Reddit Stories * Name Your Type Variables! Domain: amateurtopologist.com, Score: 71, Comments: 38 On Reddit: [5] http://goo.gl/I2uny Original: [6] http://goo.gl/yRbmO * Insane Haskell Professor on Lambda Calculus. Wait for it... Domain: youtube.com, Score: 66, Comments: 17 On Reddit: [7] http://goo.gl/uDQJS Original: [8] http://goo.gl/IauHk * criterion 0.6 produces shiny new performance reports Domain: bos.github.com, Score: 63, Comments: 8 On Reddit: [9] http://goo.gl/F2K76 Original: [10] http://goo.gl/x720h * [commit: base] master: Add traceStack :: String -> a -> a Domain: haskell.org, Score: 48, Comments: 5 On Reddit: [11] http://goo.gl/HCbf2 Original: [12] http://goo.gl/JzO3O * Elm: functional reactive web-programming (compiles to html, css, js). Just added reactive values, basic canvas support, and new interactive examples. Domain: elm-lang.org, Score: 45, Comments: 19 On Reddit: [13] http://goo.gl/mKS9a Original: [14] http://goo.gl/ASt27 * Snap 0.7 released Domain: snapframework.com, Score: 41, Comments: 1 On Reddit: [15] http://goo.gl/R3A8Y Original: [16] http://goo.gl/SVgXy * Haskell Communities and Activities Report - November 2011 edition Domain: haskell.org, Score: 35, Comments: 0 On Reddit: [17] http://goo.gl/X82AK Original: [18] http://goo.gl/CGKAr * "fix' f = f (fix' f)" vs. "fix f = let x = f x in x" Domain: groups.google.com, Score: 33, Comments: 15 On Reddit: [19] http://goo.gl/vadtO Original: [20] http://goo.gl/SQSFL * Announcing cabal-src: solve (some of) cabal dependency hell Domain: yesodweb.com, Score: 32, Comments: 15 On Reddit: [21] http://goo.gl/PIB4S Original: [22] http://goo.gl/00LZz * aeson 0.4: easier, faster, nicer Domain: github.com, Score: 31, Comments: 18 On Reddit: [23] http://goo.gl/G1J5A Original: [24] http://goo.gl/DQ4bc * Package authors: Please use Packdeps! Domain: yesodweb.com, Score: 24, Comments: 10 On Reddit: [25] http://goo.gl/bLYvt Original: [26] http://goo.gl/fNh9n * Slides from my guest lecture at Stanford Domain: blog.johantibell.com, Score: 22, Comments: 14 On Reddit: [27] http://goo.gl/ITFkN Original: [28] http://goo.gl/4w1tK Top StackOverflow Questions * How to write a Haskell function that takes a variadic function as an argument votes: 28, answers: 1 Read on SO: [29] http://goo.gl/JqZ3H * Functional lenses votes: 18, answers: 2 Read on SO: [30] http://goo.gl/Qn2Ff * Haskell : An example of a Foldable which is not a Functor? votes: 17, answers: 2 Read on SO: [31] http://goo.gl/42lSo * How does IncoherentInstances work? votes: 17, answers: 1 Read on SO: [32] http://goo.gl/O1Ha4 * Minimum specification for Haskell library type classes? votes: 16, answers: 2 Read on SO: [33] http://goo.gl/L7mO6 * Expressive and composable error types votes: 16, answers: 1 Read on SO: [34] http://goo.gl/vkoZb * Distributed Haskell state of the art in 2011? votes: 16, answers: 2 Read on SO: [35] http://goo.gl/mx0kd * Is it possible to implement liftM2 in Scala? votes: 15, answers: 1 Read on SO: [36] http://goo.gl/p6TDl * Are Haskell FlexibleInstances a stable extension to the language? votes: 15, answers: 1 Read on SO: [37] http://goo.gl/sQc37 * Is Milner let polymorphism a rank 2 feature? votes: 13, answers: 4 Read on SO: [38] http://goo.gl/kOcnW Until next time, Daniel Santa Cruz References 1. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/94240 2. http://comments.gmane.org/gmane.comp.lang.haskell.libraries/16691 3. http://comments.gmane.org/gmane.comp.lang.haskell.cafe/94245 4. http://comments.gmane.org/gmane.comp.lang.haskell.general/19038 5. http://www.amateurtopologist.com/blog/2011/10/11/name-your-type-variables/ 6. http://www.reddit.com/r/haskell/comments/mxz3k/name_your_type_variables/ 7. http://www.youtube.com/watch?v=5TMojC0Nb6A 8. http://www.reddit.com/r/haskell/comments/mw094/insane_haskell_professor_on_… 9. http://bos.github.com/criterion/ 10. http://www.reddit.com/r/haskell/comments/mx8vw/criterion_06_produces_shiny_… 11. http://www.haskell.org/pipermail/cvs-libraries/2011-November/014698.html 12. http://www.reddit.com/r/haskell/comments/muq40/commit_base_master_add_trace… 13. http://elm-lang.org/Elm.elm 14. http://www.reddit.com/r/haskell/comments/mwbvj/elm_functional_reactive_webp… 15. http://snapframework.com/blog/2011/12/01/snap-0.7-released 16. http://www.reddit.com/r/haskell/comments/mwx4t/snap_07_released/ 17. http://www.haskell.org/communities/11-2011/html/report.html 18. http://www.reddit.com/r/haskell/comments/mzbia/haskell_communities_and_acti… 19. http://groups.google.com/group/stanford-11au-cs240h/browse_thread/thread/41… 20. http://www.reddit.com/r/haskell/comments/mt7nt/fix_f_f_fix_f_vs_fix_f_let_x… 21. http://www.yesodweb.com/blog/2011/11/cabal-src 22. http://www.reddit.com/r/haskell/comments/mrz9p/announcing_cabalsrc_solve_so… 23. https://github.com/bos/aeson/blob/0.4.0.0/release-notes.markdown 24. http://www.reddit.com/r/haskell/comments/mvtmk/aeson_04_easier_faster_nicer/ 25. http://www.yesodweb.com/blog/2011/12/please-use-packdeps 26. http://www.reddit.com/r/haskell/comments/mvp4w/package_authors_please_use_p… 27. http://blog.johantibell.com/2011/11/slides-from-my-guest-lecture-at.html 28. http://www.reddit.com/r/haskell/comments/mvoqd/slides_from_my_guest_lecture… 29. http://stackoverflow.com/questions/8353845/how-to-write-a-haskell-function-… 30. http://stackoverflow.com/questions/8307370/functional-lenses 31. http://stackoverflow.com/questions/8359115/haskell-an-example-of-a-foldable… 32. http://stackoverflow.com/questions/8371499/how-does-incoherentinstances-work 33. http://stackoverflow.com/questions/8320039/minimum-specification-for-haskel… 34. http://stackoverflow.com/questions/8320855/expressive-and-composable-error-… 35. http://stackoverflow.com/questions/8362998/distributed-haskell-state-of-the… 36. http://stackoverflow.com/questions/8366518/is-it-possible-to-implement-lift… 37. http://stackoverflow.com/questions/8367423/are-haskell-flexibleinstances-a-… 38. http://stackoverflow.com/questions/8296695/is-milner-let-polymorphism-a-ran…

1 0

terminateProcess leaves zombie processes around
by Dan Rosén 08 Dec '11

08 Dec '11

Hi Haskell-Cafe, I'm using Haskell to run a lot of instances of an Automated Thorem Prover, eprover. I have pasted a smaller version of my program at http://hpaste.org/54954. It runs eprover sequentially on all input files, with a timeout of 100ms. Unfortunately, it leaves a lot of zombie processes around, probably due to the fact that terminateProcess fails to terminate them, even though eprover terminates on SIGTERM. I have tried to use System.Timeout.timeout around readProcess, but without surprise it did not work. Another way of doing it is to use the timeout from gnu-coreutils, but the timeout resolution is in seconds (same with eprover's flag --cpu-limit). Any ideas how I could write my code to get a clean termination of this process? Best, Dan Rosén

5 8

PhD position at Ghent University
by Tom Schrijvers 07 Dec '11

07 Dec '11

The Programming Languages Group of Ghent University invites applicants for a PhD position. This position centers around the modular treatment of side-effects in purely functional programs and models. It is part of the project "Modular handling of effects in purely functional programs and models" under the direction of Tom Schrijvers. The successful applicant has a master degree in Computer Science or equivalent. Ideally, she/he will also have a strong, documented interest in doing research. Strong problem-solving and programming skills are essential. Prior knowledge of purely functional programming (e.g., Haskell) and models of side-effects (e.g., monads) is an advantage. The PhD position is for 4 years. It starts between January and October 2012. The position is a fully-funded post. The salary is compatible with other Belgian PhD rates and among the better ones in Europe and abroad. For more information, see: http://users.ugent.be/~tschrijv/phdposition2.html -- prof. dr. ir. Tom Schrijvers Programming Languages Group Department of Applied Mathematics and Computer Science University of Ghent Krijgslaan 281 S9 9000 Gent Belgium Phone: +32 9 264 4805 http://users.ugent.be/~tschrijv/

1 0

Neither of the sparks are converted into OS threads but parallelization happens surprisingly!!!
by Burak Ekici 07 Dec '11

07 Dec '11

Dear List, I have a point misunderstood! I am using second generation strategies of Haskell to parallelize some number of algorithms in Haskell. The missing point here is that: In some cases, neither of created sparks are converted into OS threads, but parallelization happens surprisingly, when I use threadscope to see what had happened during the evaluation. What happened to me was that 2 sparks were created one of which was pruned, none of which was converted into OS threads and the last one was missing, however, parallelism happened!!! I wonder what is the reason for this? Could someone aware, please shed light on the issue? Thanks in advance. Saluti, Burak.

1 0

Haskell at University in Munich
by Bartosz Wójcik 06 Dec '11

06 Dec '11

Hello Haskell Cafe, I would be grateful for any information regarding Haskell (or at least Functional Programming) lectures at Universities near to Munich, Germany (Master or Bachelor). Unconfirmed information I've got regarding LMU and TUM are not promising. If Munich and 200 km circle do not provide with any offer, perhaps you may know what is available in Europe, limiting language of study to [German, English, Polish]? Best regards, Bartek

2 2

Re: [Haskell-cafe] Haskell at University in Munich
by Janis Voigtländer 06 Dec '11

06 Dec '11

Am 05.12.2011 12:00, schrieb <bartek(a)sudety.it>: > Hello Haskell Cafe, > > I would be grateful for any information regarding Haskell (or at least > Functional Programming) lectures at Universities near to Munich, Germany > (Master or Bachelor). Unconfirmed information I've got regarding LMU and TUM > are not promising. Is Munich really that bad? FP'ers at LMU and TUM, please speak up. (I know that at least research-wise there are quite a few around there, though I don't know what they do in teaching.) > If Munich and 200 km circle do not provide with any offer, perhaps Less than 200 km from Munich: http://db.inf.uni-tuebingen.de/teaching/ws1112/afp Also, Germany extends farther than 200 km beyond Munich. :-) Say, Bonn: http://www.iai.uni-bonn.de/~jv/teaching/dp11/ http://www.iai.uni-bonn.de/~jv/teaching/ffp/ > you may know what is available in Europe, limiting language of study > to [German, English,Polish]? The thread Sean pointed to may provide information on that. Obvious candidates are Utrecht and Chalmers, both teaching in English I suppose, at least at Master level. Best, Janis. -- Jun.-Prof. Dr. Janis Voigtländer http://www.iai.uni-bonn.de/~jv/ mailto:jv@iai.uni-bonn.de

2 1

Haddock and the qualified imports
by Yves Parès 06 Dec '11

06 Dec '11

Hi, I noticed some time ago the fact that qualified imports doesn't affect the generated documentation. It's kind of clumsy in case of libraries that define a lot of synonyms (vector and bytestring come in my mind first). For instance, in the package utf8-string: http://hackage.haskell.org/packages/archive/utf8-string/0.3.7/doc/html/Data… Here, the documentation doesn't say that the utf8-string/Data.ByteString.UTF8.ByteString datatype used all along comes in fact from Data.ByteString. If it were instead a new implementation of ByteString (as for bytestring/Data.ByteString.Char8.ByteString) the documentation would look exactly the same, so to disambiguate to reader has to crawl through the code to get to the initial definition. (clicking on a 'ByteString' doesn't even redirect you to the original bytestring/Data.ByteString page) It should be written that this 'ByteString' is not a newly defined type but instead a re-exportation. It's even worse when you see the doc of a module that uses in the meantime lazy and strict ByteStrings, or normal and unboxed/storable/<insert flavour here> vector: you have to hover the type name to see which haddock page it points to. In that case, a solution might be to indicate on top of the doc page that it uses another module as a qualified import, and to keep the prefixes in the function signatures.

3 6

Where threadSleep is defined?
by dokondr 06 Dec '11

06 Dec '11

Hi, I need to make the current process (executing thread) go to sleep for a given amount of time. Can't find where threadSleep is defined. Thanks!

3 3

List x ByteString x Lazy Bytestring
by John Sneer 06 Dec '11

06 Dec '11

Hello Café, I've used Haskell and GHC to solve particular real life application. 4 tools were developed and their function is almost the same - they modify textual input according to patterns found in the text. Thus, it is something like a compiler, the result is also a text and it is not parsed to tokens as patterns appear on a different level. The tools differ in tasks and number of modifications performed, otherwise, in principal, they are very much similar. I used lists (Prelude, Data.List) to develop the tools. After successfully completing the development, I've started to optimize the code to make the tools faster. After modification of some algorithms (which dropped the processing time notably), I started to change data structures. I swapped lists with lazy bytestrings. Nevertheless, what an unpleasant surprise, the processing speed dropped down, significantly / more then 30% time needed). So my questions follow: - What kind of application is lazy bytestring suitable for? - Would it be worth using strict bytestring even if input files may be large? (They would fit in memory, but may consume whole) - If bytestring is not suitable for text manipulation, is there something faster than lists? - It would be nice to have native sort for lazy bytestring - would it be slower than pack $ Data.List.sort $ unpack ? - If bytestring is suitable for text manipulation could we have some hGetTextualContents which translates Windows EOL (CR+LF) to LF? I'm sorry if the answers are obvious. Could anyone point me to some article/pages I could read about? Thanks and regards, John -- http://www.fastmail.fm - A fast, anti-spam email service.

7 9

Complete package description list
by Shakthi Kannan 06 Dec '11

06 Dec '11

Hi, I would like to know: 1. The correct source to get the complete list of available Haskell package descriptions 2. Any feed or notification mechanism to get newer updates on packages How often does the 00-index.tar.gz file from: http://hackage.haskell.org/packages/archive/00-index.tar.gz get updated? Or if there is a newer version, where is it made available? Given 00-index.tar.gz, and using the following RSS feed: http://hackage.haskell.org/packages/archive/recent.rss give me the complete list of available packages? Appreciate any suggestions in this regard, Thanks! SK -- Shakthi Kannan http://www.shakthimaan.com

3 4

ANNOUNCE: monad-control-0.3
by Bas van Dijk 06 Dec '11

06 Dec '11

Hello, I just released monad-control-0.3. The package for lifting control operations (like catch, bracket, mask, alloca, timeout, forkIO, modifyMVar, etc.) through monad transformers: http://hackage.haskell.org/package/monad-control-0.3 It has a new and improved API which is: * easier to understand by explicitly representing the monadic state using type families. * 60 times faster than the previous release! * more general because control operations can now, not only be lifted from IO, but from any base monad (ST, STM, etc.) I also released a new package: lifted-base: http://hackage.haskell.org/package/lifted-base-0.1 It provides lifted versions of functions from the base library. Currently it exports the following modules: * Control.Exception.Lifted * Control.Concurrent.Lifted * Control.Concurrent.MVar.Lifted * System.Timeout.Lifted These are just modules which people have needed in the past. If you need a lifted version of some function, just ask me to add it or send me a patch. Note that Peter Simons just discovered that these packages don't build with GHC-7.0.4 (https://github.com/basvandijk/monad-control/issues/3) I just committed some fixes which enable them to be build on GHC >= 6.12.3. Hopefully I can release these fixes this weekend. Regards, Bas

6 18

Re: [Haskell-cafe] How to get a file path to the program invoked?
by Greg Weber 06 Dec '11

06 Dec '11

In addition to argv[0] http://hackage.haskell.org/packages/archive/system-argv0/0.1/doc/html/Syste… There is also this package: http://hackage.haskell.org/packages/archive/FindBin/0.0.5/doc/html/System-E… System-Argv0 has special cases for windows- FindBin may not work there.

1 0

GHCi and Cairo on Windows
by smeltzek＠eecs.oregonstate.edu 06 Dec '11

06 Dec '11

In effort to keep my work cross-platform, I am trying to get GHCi and Cairo working together nicely on Windows (as a back-end to Diagrams, if it matters.) When loading the library in GHCi I get the following error: Loading package cairo-0.12.2 ... linking ... ghc: unable to load package `cairo-0.12.2' I am able to build, link, and execute successfully using 'ghc --make' so I know the libraries are installed correctly. I'm using GHC as packaged in the most recent version of the Haskell Platform and the most recent all-in-one Windows bundle of GTK. I've seen quite similar errors reported months ago with no apparent solution. Any help would be appreciated! --Karl

3 2

Re: [Haskell-cafe] Poll: Do you want a mascot? -- please stop this
by Giovanni Tirloni 05 Dec '11

05 Dec '11

On Wed, Nov 23, 2011 at 5:52 PM, heathmatlock <heathmatlock(a)gmail.com>wrote: > On Wed, Nov 23, 2011 at 1:40 PM, Alexander Bernauer < > alex-haskell(a)copton.net> wrote: > >> Yes >> >> PS: Why not using Doodle for the poll? >> > > Email is an easy way to make sure nobody votes twice. > 1. It's unlikely to get feedback from the larger Haskell community 2. It floods people with email they don't care (unless they care to keep track of the results) 3. One can just as easily create throw-away emails, subscribe to the list and answer the poll 4. etc... My suggestion is to create a poll somewhere else and let it run for at least a month. Or a more elaborated survey with additional questions trying to capture the community's feeling toward a masket and what kind. I don't think we are in a hurry to get a mascot here so let's take the time and do it properly. -- Giovanni

7 8

Re: [Haskell-cafe] "could not create compact unwind"
by Mark Lentczner 05 Dec '11

05 Dec '11

The ld warning is benign. You can safely ignore it. It is a known issue with GHC and the latest Mac OS X tool chain, and we are stuck with it for awhile: http://hackage.haskell.org/trac/ghc/ticket/5019 The best way to remove versions of Haskell on a Mac is now my shiny new Mac uninstaller! I just put out a "release candidate" yesterday. You can find it here: Source: UninstallHS.hs (just runhaskell this)Executable: uninstall-hs.tgz (unpack and run if your ghc is broken) Running without will just list what's there and suggest what to do next. It is "dry-run" by default. - Mark PS.: "rm -rf ~/.ghc" only removes the package databases, not the packages themselves. It also removes your ghci configuration, so I don't recommend it.

1 0

Re: [Haskell-cafe] How to get a file path to the program invoked?
by dokondr 05 Dec '11

05 Dec '11

Balazs, thanks for your comments! The first comment works just fine. With </> operator I get this: Main System.Environment.Executable System.FilePath> "/abc" </> "/" "/" Instead of getting "/abc/" I get "/". What am I doing wrong? On Mon, Dec 5, 2011 at 6:03 PM, Balazs Komuves <bkomuves(a)gmail.com> wrote: > > Two small comments: > > 1) This should work on Windows too, if you just leave out the word "Posix" > from the source: > import System.FilePath (splitFileName) > > 2) In general when dealing with paths, use the </> operator (from > System.FilePath) > instead of ++ "/" ++ > > Balazs > > > On Mon, Dec 5, 2011 at 1:44 PM, dokondr <dokondr(a)gmail.com> wrote: > >> This is how I finally solved this problem for POSIX complaint system: >> >> -- >> -- TestRun >> -- >> module Main where >> import System.Cmd (rawSystem) >> import System.Directory (getCurrentDirectory) >> import System.Environment.Executable (ScriptPath(..), getScriptPath) >> import System.FilePath.Posix (splitFileName) >> >> main = do >> >> path <- getMyPath >> putStrLn $ "myPath = " ++ path >> let cmdLine = path ++ "args.sh" >> rawSystem cmdLine ["iphone", "test-twitts.txt"] >> >> {-- >> data ScriptPath Source >> >> Constructors: >> Executable FilePath it was (probably) a proper compiled executable >> RunGHC FilePath it was a script run by runghc/runhaskell >> Interactive we are in GHCi >> --} >> >> getMyPath = do >> curDir <- getCurrentDirectory -- from System.Directory >> scriptPath <- getScriptPath -- from System.Environment.Executable >> let path = getMyPath' scriptPath curDir >> return path >> >> getMyPath' (Executable path) _ = fst (splitFileName path) >> getMyPath' (RunGHC path) _ = fst (splitFileName path) >> getMyPath' Interactive curDir = curDir++"/" >> >> >>

4 4

writeFile: commitBuffer: invalid argument (Illegal byte sequence)
by dokondr 05 Dec '11

05 Dec '11

Hi, In GHC 7.0.3 / Mac OS X when trying to: writeFile "someFile" "(Hoping You Have A iPhone When I Do This) Lol Sleep Is When You Close These ---> \55357\56384" I get: commitBuffer: invalid argument (Illegal byte sequence) The string I am trying to write can also be seen here: http://twitter.com/#!/search/Hoping%20You%20Have%20A%20iPhone%20When%20I%20…<http://twitter.com/#%21/search/Hoping%20You%20Have%20A%20iPhone%20When%20I%…> It looks like 'writeFile' can not write unicode characters. Any workarounds? Thanks! Dmitri

3 6

FLOPS 2012: final call for papers & deadline extension
by Tom Schrijvers 05 Dec '11

05 Dec '11

Final Call For Papers ===================== _EXTENDED SUBMISSION DEADLINE : December 16, 2011_ *Eleventh International Symposium on Functional and Logic Programming (FLOPS 2012)* May 23-25, 2012 Kobe, Japan [http://www.org.kobe-u.ac.jp/flops2012/] FLOPS is a forum for research on all issues concerning declarative programming, including functional programming and logic programming, and aims to promote cross-fertilization and integration between the two paradigms. Previous FLOPS meetings were held in Fuji Susono (1995), Shonan Village (1996), Kyoto (1998), Tsukuba (1999), Tokyo (2001), Aizu (2002), Nara (2004), Fuji Susono (2006), Ise (2008), and Sendai (2010). Topics ====== FLOPS solicits original papers in all areas of functional and logic programming, including (but not limited to): - Declarative Pearls: new and excellent declarative programs with illustrative applications. - Language issues: language design and constructs, programming methodology, integration of paradigms, interfacing with other languages, type systems, constraints, concurrency and distributed computing. - Foundations: logic and semantics, rewrite systems and narrowing, type theory, proof systems. - Implementation issues: compilation techniques, memory management, program analysis and transformation, partial evaluation, parallelism. - Applications: case studies, real-world applications, graphical user interfaces, Internet applications, XML, databases, formal methods and model checking. The proceedings will be published as an LNCS volume. The proceedings of the previous meeting (FLOPS 2010) were published as LNCS 6009. PC co-Chairs ============ - Tom Schrijvers (Ghent University, Belgium) - Peter Thiemann (University of Freiburg, Germany) PC Members ========== - Salvador Abreu (University of Evora, Portugal) - Thorsten Altenkirch (University of Nottingham, UK) - Sebastian Brand (NICTA, Australia) - Giuseppe Castagna (CNRS Univ Paris 7, France) - Sebastian Fischer (Germany) - Marco Gavanelli (University of Ferrara, Italy) - Joxan Jaffar (National University of Singapore, Singapore) - Barry Jay (University of Sydney, Australia) - Andy King (University of Kent, UK) - Claude Kirchner (INRIA, France) - Neelakantan R. Krishnaswami (Microsoft Cambridge, UK) - Yulya Lierler (University of Kentucky, USA) - Keiko Nakata (Tallinn University of Technology, Estonia) - Peter Schneider-Kamp (University of Southern Denmark, Denmark) - Olin Shivers (Northeastern University, USA) - Paul Tarau (University of Northern Texas, USA) - Kazunori Ueda (Waseda University, Japan) - Meng Wang (Chalmers Technical University, Sweden) General Chair and Local co-Chairs ================================= - Naoyuki Tamura (Kobe University, Japan) - Mutsunori Banbara (Kobe University, Japan) - Katsutoshi Hirayama (Kobe University, Japan) Submission ========== Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. Submissions should fall into one of the following categories: - Regular research papers: they should describe new results and will be judged on originality, correctness, and significance. - System descriptions: they should contain a link to a working system and will be judged on originality, usefulness, and design. Submissions must be written in English and can be up to 15 pages long, though pearls are typically considerably shorter. Authors are required to use LaTeX2e and the Springer llncs class file, available at [http://www.springer.de/comp/lncs/authors.html] Regular research papers should be supported by proofs and/or experimental results. In case of lack of space, this supporting information should be made accessible otherwise (e.g., a link to a web page, or an appendix). Papers should be submitted electronically at [https://www.easychair.org/conferences/?conf=flops2012] Important Dates =============== - Submission deadline : December 16, 2011 (EXTENDED) - Author notification : February 3, 2012 - Camera-ready copy : March 2, 2012 Place and Related Events ======================== Takikawa Memorial Hall, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 Japan. The 23rd International Conference on Rewriting Techniques and Applications (RTA 2012) and satellite workshops including WFLP 2012 will be held in the week after FLOPS at Nagoya, Japan. Some Previous FLOPS =================== - FLOPS 2010, Sendai: [http://www.kb.ecei.tohoku.ac.jp/flops2010/] - FLOPS 2008, Ise: [http://www.math.nagoya-u.ac.jp/~garrigue/FLOPS2008/] - FLOPS 2006, Fuji Susono: [http://hagi.is.s.u-tokyo.ac.jp/FLOPS2006/] Sponsors ======== - Japan Society for Software Science and Technology (JSSST) SIGPPL In Cooperation with =================== - ACM SIGPLAN - Asian Association for Foundation of Software (AAFS) - Association for Logic Programming (ALP)

1 0

Re: [Haskell-cafe] How to get a file path to the program invoked?
by dokondr 05 Dec '11

05 Dec '11

This is how I finally solved this problem for POSIX complaint system: -- -- TestRun -- module Main where import System.Cmd (rawSystem) import System.Directory (getCurrentDirectory) import System.Environment.Executable (ScriptPath(..), getScriptPath) import System.FilePath.Posix (splitFileName) main = do path <- getMyPath putStrLn $ "myPath = " ++ path let cmdLine = path ++ "args.sh" rawSystem cmdLine ["iphone", "test-twitts.txt"] {-- data ScriptPath Source Constructors: Executable FilePath it was (probably) a proper compiled executable RunGHC FilePath it was a script run by runghc/runhaskell Interactive we are in GHCi --} getMyPath = do curDir <- getCurrentDirectory -- from System.Directory scriptPath <- getScriptPath -- from System.Environment.Executable let path = getMyPath' scriptPath curDir return path getMyPath' (Executable path) _ = fst (splitFileName path) getMyPath' (RunGHC path) _ = fst (splitFileName path) getMyPath' Interactive curDir = curDir++"/" -- All the best, Dmitri O. Kondratiev "This is what keeps me going: discovery" dokondr(a)gmail.com http://sites.google.com/site/dokondr/welcome

1 0

Anonymous, Unique Types, maybe
by Scott Lawrence 04 Dec '11

04 Dec '11

(Sorry if this email is rather unclear - I know my desired end result, but neither how to acheive nor explain it well. Here goes.) I'm processing lists, using them sortof as streams. (Whether that's a good idea isn't the issue here - but let me know if it isn't!) Fundamentally, there are two types of operations (at least, that are relevant here) - those that change the length of the list and those that don't. Some operators might take more than one list/stream as an argument, combining them in some way or another. Obviously, if the lists were different lengths, the operator would fail. I don't want that to happen at run time, so I want to check for it statically, presumably via the type system. I could do this manually: type AList = [Event] type BList = [Event] type CList = [Event] myMapish :: AList -> AList mySelect :: AList -> (Event -> Bool) -> BList myOtherSelect :: BList -> CList but I'd rather not have to manually define a new type for every new list length: myMapish :: List a -> List a mySelect :: List a -> List ? The '?' would be an anonymous, unique type - unless there's a better way to accomplish this. Hope that was clear, and thanks (as always) for the help (and being awesome). -- Scott Lawrence

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ismzero operator possible without equal constraint
by edgar klerks 04 Dec '11

04 Dec '11

Hi list, I am using MonadSplit (from http://www.haskell.org/haskellwiki/New_monads/MonadSplit ) for a project and now I want to make a library out of it. This seems to be straightforward, but I got stuck when I tried to move miszero out of the class: miszero :: m a -> Bool It tests if the provided monad instance is empty. My naive attempt was: miszero :: (Eq (m a), MonadPlus m) => m a -> Bool miszero = ( == mzero ) This works, but not correctly. It adds an Eq constraint that is unneeded. I would prefer to have something like: miszero :: MonadPlus m => m a -> Bool Because I am not comparing the contents of the monad. I don't even touch it. Is this possible to write? with kind regards, Edgar

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ANNOUNCE: Haskell Communities and Activities Report (21st ed., November 2011)
by Janis Voigtländer 04 Dec '11

04 Dec '11

On behalf of all the contributors, I am pleased to announce that the Haskell Communities and Activities Report (21st edition, November 2011) is now available in PDF and HTML formats: http://haskell.org/communities/11-2011/report.pdf http://haskell.org/communities/11-2011/html/report.html Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. I hope you will find it as interesting a read as I did. If you have not encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects, and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and sometimes in time for the actual deadline to the call. The editor collects all the contributions into a single report and feeds that back to the community. When I try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ========================================= End of April 2012: target deadline for contributions to the May 2012 edition of the HC&A Report ========================================= Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to "register" with the editor for a simple e-mail reminder in April (you could point me to them as well, and I can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Janis Voigtlaender <hcar at haskell.org>

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Weird interaction between literate haskell, ghci and OverloadedStrings
by Erik de Castro Lopo 03 Dec '11

03 Dec '11

Hi, I'm working on a literate haskell document (actually TeX, but the example below is just test) and I'm using ByteStrings in the code. I know I can do: ghci -XOverloadedStrings file.lhs or, after ghci is running I can do: Main> :set -XOverloadedStrings but I'd like to embed a directive in the file so that when loaded in GHCi, I will automatically get OverloadedStrings. This is mainly so that it JustWorks(tm) when I pass the file on to someone else. Is there a way to do this? There is a short example file below. I'm using ghc-7.0.4 from Debian testing. Cheers, Erik ----------8<----------8<----------8<----------8<---------- > {-# LANGUAGE OverloadedStrings #-} This is just text that that ghc/ghci should ignore > import Data.ByteString (ByteString) > import qualified Data.ByteString.Char8 as BS Simple function: > newlineCount :: ByteString -> Int > newlineCount bs = BS.foldl foldFun 0 bs > where foldFun s ch = if ch == '\n' then s + 1 else s Once this file is loaded, I should be able to do this: newlineCount "abcd\ncdead\nasdasd\n" ----------8<----------8<----------8<----------8<---------- -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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cabal install --hyperlink-source ?
by Johannes Waldmann 02 Dec '11

02 Dec '11

Hello. I can do "cabal install --enable-documentation" which is nice because it does configure, build, haddock and copy in one go, but I don't see how to pass options from "cabal install" to "cabal haddock" (e.g., --hyperlink-source) Any hints appreciated, J.W.

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exhibit space at CeBIT Open Source 2012
by Mathias Huber 02 Dec '11

02 Dec '11

Dear Haskellers, this might interest those not too far from Hannover, Germany: http://www.linux-magazine.com/Online/News/CeBIT-Open-Source-2012-Call-for-P… "CeBIT welcomes open source projects to Hannover, Germany! The show organization and Linux Magazine are calling for open source projects to apply for free exhibit space at CeBIT Open Source 2012." There is also a call for papers: http://www.linux-magazine.com/Online/News/CeBIT-2012-Call-for-Papers-Open-S… Best, Mathias

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Program used for debugging
by Yves Parès 02 Dec '11

02 Dec '11

Hey, What do you mostly use for debugging? Simple calls to Debug.Trace.trace? Hpc? Hood?

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PLPV 2012: Call for participation
by Nikhil Swamy 02 Dec '11

02 Dec '11

Call for Participation ====================== PLPV 2012 The Sixth ACM SIGPLAN Workshop Programming Languages meets Program Verification 24th January, 2012 Philadelphia, USA (Affiliated with POPL 2012) http://research.microsoft.com/en-us/um/people/nswamy/plpv12 You are cordially invited to PLPV 2012. The goal of PLPV is to foster and stimulate research at the intersection of programming languages and program verification, by bringing together experts from diverse areas like types, contracts, interactive theorem proving, model checking and program analysis. Work in this area typically attempts to reduce the burden of program verification by taking advantage of particular semantic or structural properties of the programming language. Examples include dependently typed programming languages, which leverage a language's type system to specify and check richer than usual specifications or extended static checking systems which incorporate contracts with either static or dynamic contract checking. Registration ============ To register for PLPV 2012, please follow the instructions at: https://regmaster3.com/2012conf/POPL12/register.php The early registration deadline is December 24, 2011. Hotel Information ================= PLPV will be co-located with POPL at the Sheraton Society Hill Hotel in Philadelphia. Please visit POPL's web site to make reservations at the special conference rate. Program ======= Session 1: 9:00am-10:00am LTL types FRP: Linear-time Temporal Logic Propositions as Types, Proofs as Functional Reactive Programs Alan Jeffrey A Hoare Calculus for the Verification of Synchronous Languages Manuel Gesell and Klaus Schneider Session 2: 10:30am-12:00pm Invited talk: Could We Verify an Information-flow Computer? Benjamin C. Pierce University of Pennsylvania Lunch: 12:00pm-2:00pm (not provided) Session 3: 2:00pm-3:30pm Reflexive Toolbox for Regular Expression Matching Vladimir Komendantsky Formal Network Packet Processing with Minimal Fuss: Invertible Syntax Descriptions at Work Reynald Affeldt, David Nowak and Yutaka Oiwa The VerCors project - setting up basecamp Afshin Amighi, Stefan Blom, Marieke Huisman and Marina Zaharieva-Stojanovski Session 4: 4:00pm-5:00pm Dependent Interoperability Peter-Michael Osera, Vilhelm Sjoberg and Steve Zdancewic. Equational Reasoning about Programs with General Recursion and Call-by-value Semantics Garrin Kimmell, Aaron Stump, Harley Eades, Peng Fu, Tim Sheard, Stephanie Weirich, Chris Casinghino, Vilhelm Sjoberg, Nathan Collins and Ki Yung Ahn

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Using QuickCheck to test against a database
by Oliver Charles 02 Dec '11

02 Dec '11

Hi! I've just spent my evening trying to use QuickCheck properties to test the database accessing functions in a project I'm working on at the moment. I've got some stuff that's working, and I wanted to see what the cafe thought about it, and if anyone had any suggestions or critiscm that can help me make it even better! I got here by trying to figure out how I want to test my application. At first I saw 2 options: use a test database and assume it exists, or have each test setup the data it needs. I like the latter more, because it minimises dependence on the outside world. So I got down to writing some HUnit tests and then had a wave of inspiration... what if I didn't even define the data, but let QuickCheck do that for me? Here's what I came up with - note the code here is somewhat paraphrased for brevity: data DBState a = DBState { initDb :: IO () , entity :: a } This type stores an action that initialises the database with enough data such that it contains whatever 'entity' is. For example, 'DBState Person' knows how to insert a specific person into the database, and carries along an in-memory log. Continuing with the Person idea, I then went and made an Arbitrary instance for DBState Person: instance Arbitrary (DBState Person) where arbitrary = do l <- Person <$> arbitrary `suchThat` (not . null) return $ DBState (void $ insertPerson l) p where insertPerson p = doSql "INSERT INTO person (name) VALUES (?)" [ personName p l ] Then it's just a case of defining some properties: prop_allPersons = monadicIO $ do dbState <- pick arbitrary :: Gen [Person] fetched <- run $ initDb `mapM` dbState >> findAllPersons assert $ fetched `eqSet` (entity `map` dbState) where eqSet a b = all (`elem` a) b && all (`elem` b) a Voila! For any database, 'findAllPersons' returns all persons. Now... onto my own critiscisms with this. Firstly, way too much boiler plate. You have to remember to apply all of the states of your arbitrary instances, which is a pain, and guaranteed to be missed. At first I thought DBState looks like it's basically a writer/IO monad, but then I couldn't actually figure out the monoid to write to. In this case it's just [Person], but in more complex property we might need 2 types of entities (for example, to ensure a join worked correctly) which makes this list heterogenous. Secondly, the initDb action is sensitive to the order actions are sequenced. Presumably, I want to test against a database that's as accurate to production as possible, which means I want foreign keys enabled. If things are initialized in the wrong order, it violates the foreign key constraint, and it's a burden if people have to determine the correct order. One solution here is to make use of deferrable constraints, but support for these is flakey at best (and it doesn't work for bracketting tests with BEGIN; ROLLBACK). These problems just make the properties harder, but they don't seem to impede the quality or usefulness of the tests. I really want to make this work, because the idea of it is quite beautiful to me. Though that might be partly because this is my first time really using QuickCheck, so I'm getting the "oh wow this is sweeeet" effect at the same time ;) Would love to hear peoples thoughts! - Ollie

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List Fusion of concatMap
by Joachim Breitner 01 Dec '11

01 Dec '11

Hi, in further attempts to get a better understanding of list fusion, I am investigating under what conditions, calls to concat and concatMap succesfully fusion away. Here is my test code: import System.Exit func0 :: Int -> Bool func0 n = any (>5) [1..n] {-# NOINLINE func0 #-} func1 :: Int -> Bool func1 n = any (>5) (concatMap (\m -> [1..m]) [1..n]) {-# NOINLINE func1 #-} func2 :: Int -> Bool func2 n = any (>5) (concat (map (\m -> [1..m]) [1..n])) {-# NOINLINE func2 #-} func3 :: Int -> Bool func3 n = any (>5) [ i | m <- [1..n] , i <- [1..m]] {-# NOINLINE func3 #-} func4 :: Int -> Bool func4 n = any (>5) ( let ok m = [ i | i <- [1..m] ] in concatMap ok [1..n] ) {-# NOINLINE func4 #-} main = if func0 10 && func1 10 && func2 10 && func3 10 && func4 10 then exitSuccess else exitFailure I deliberately did not use any putStr statements in main, so that I can easily spot list types in the output of ghc -fext-core. The use of "any" and "[...]" represent any fusion-enabled producers or consumers; these are just very well-behaving and easy to spot in the core output. Here are my obeservations: * The code generated for func0 does not use any lists at all, but rather one recursive (even tail-recursive) function, as expected. This was basically a test whether I am indeed able to observe list fusion. * func1 and func2 are not fused successfully; both core outputs still contain mentions of [] (search for ZMZN; is there a tool that does this unescaping for me? ghc-core does not, it seems.) * Now the surprising fact: func3 does without any lists! The code generated contains two nested recursive functions, the inner one even tail recursive (and the outer one could have been made tail-recursive, it seems, but that would be a different issue). * func4, which is a direct one-step translation of func3 according to the semantic rules of list comprehension in the haskell report, again is not fused completely. Now I wonder: How do I need to phrase the function with concatMap such that fusion works? Does ghc treat list comprehensions differently here? Do the rewrite rules need work so that func1 and func2 do fuse correctly? Thanks for your attention, Joachim -- Joachim "nomeata" Breitner mail(a)joachim-breitner.de | nomeata(a)debian.org | GPG: 0x4743206C xmpp: nomeata(a)joachim-breitner.de | http://www.joachim-breitner.de/

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Re: [Haskell-cafe] How to get a file path to the program invoked?
by dokondr 01 Dec '11

01 Dec '11

Balazs, thanks! It's great that these packages exist! On Thu, Dec 1, 2011 at 11:17 PM, Balazs Komuves <bkomuves(a)gmail.com> wrote: > > Hello, > > I'm not subscribed to haskell cafe, but I browse the archives sometimes. > > As Simon Hengel wrote there, there are two packages on Hackage > trying to solve this exact problem (since GHC and the standard library > does not provide the necessary information): > > http://hackage.haskell.org/package/executable-path > http://hackage.haskell.org/package/FindBin > > (Hackage is down at the moment, so I'm not completely sure about the > second link). > I'm the author of the first one. > > Balazs > >

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