- Haskell-Cafe - Haskell.org

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…

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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

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