February 2013 - Haskell-Cafe

Budapest Haskell meetup Feb 14
by Zsolt Dollenstein 09 Feb '13

09 Feb '13

[sorry for the possible double-post, apparently posting through the google groups interface is futile] Hi, In case someone is around Budapest on the 14th of Feb (Thursday), there is going to be a Haskell meetup in the heart of the city. Hamish Mackenzie will talk about yet-to-be-released Leksah features and David Terei will explain how his memcache client works. Details and sign up at http://www.meetup.com/fp-bud/events/102245252/ Hope to see you there :) Zsolt

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1st CFP SBLP 2013 (17th Brazilian Symposium on Programming Languages)
by Andre Rauber Du Bois 09 Feb '13

09 Feb '13

[Apologies if you receive multiple copies of this CFP] ======================================================= CALL FOR PAPERS 17th BRAZILIAN SYMPOSIUM ON PROGRAMMING LANGUAGES Brasília, Distrito Federal, Brazil September 29th to October 4th, 2013 http://cbsoft2013.cic.unb.br/sblp ======================================================== IMPORTANT DATES Paper abstract submission (15 lines): April 19th Full paper submission: April 26th, 2013 Notification of acceptance: May 31st, 2013 Final papers due: June 28th, 2013 INTRODUCTION The 17th Brazilian Symposium on Programming Languages, SBLP 2013, will be held in Brasília, Brazil, on September 29th to October 4th, 2013. SBLP provides a venue for researchers and practitioners interested in the fundamental principles and innovations in the design and implementation of programming languages and systems. The symposium will be part of the 4th Brazilian Conference on Software: Theory and Practice, CBSoft 2013, http://cbsoft2013.cic.unb.br/, which will host four traditional, well-established symposia: * XXVII Brazilian Symposium on Software Engineering (SBES) * XVII Brazilian Symposium on Programming Languages (SBLP) * XVI Brazilian Symposium on Formal Methods (SBMF) * VII Brazilian Symposium on Components, Software Architecture and Software Reuse (SBCARS) SBLP 2013 invites authors to contribute with technical papers related (but not limited) to: * Program generation and transformation, including domain-specific languages and model-driven development in the context of programming languages. * Programming paradigms and styles, including functional, object-oriented, aspect-oriented, scripting languages, real-time, service-oriented, multithreaded, parallel, and distributed programming. * Formal semantics and theoretical foundations, including denotational, operational, algebraic and categorical. * Program analysis and verification, including type systems, static analysis and abstract interpretation. * Programming language design and implementation, including new programming models, programming language environments, compilation and interpretation techniques. SUBMISSIONS Contributions should be written in Portuguese or English. We solicit papers that should fall into one of two different categories: full papers, with at most 15 pages, or short papers, with at most 5 pages. Full papers submitted in English will be published in a volume of Lecture Notes in Computer Science (LNCS), by Springer (pending approval). For this reason, all papers must be prepared using the LNCS template, available at http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0. We encourage the submission of short papers reporting on partial results of on-going master dissertations or doctoral theses. All accepted papers will be published in the conference proceedings distributed in a digital media by the CBSOFT organizers. Submissions should be done using SBLP 2013 installation of the EasyChair conference mangement system at http://www.easychair.org/conferences/?conf=sblp2013. As in previous editions, a journal special issue, with selected papers from accepted contributions, is anticipated. Selected papers from 2003 to 2008 editions of SBLP were published in special issues of the Journal of Universal Computer Science, by Springer. The post-proceedings of SBLP from 2009 to 2012, also with selected papers from the conference proceedings, are being edited as special issues of Science of Computer Programming, published by Elsevier. CBSOFT CHAIRS Genaina Nunes Rodrigues, UnB Rodrigo Bonifácio, UnB Diego Aranha, UnB PROGRAMME CHAIRS André Rauber Du Bois, UFPel Phil Trinder, Glasgow University PROGRAMME COMMITTEE Alberto Pardo, Univ. de La Republica Alex Garcia, IME Alvaro Freitas Moreira, UFRGS André Rauber Du Bois, UFPel (co-chair) Andre Santos, UFPE Carlos Camarao, UFMG Christiano Braga, UFF Edwin Brady, University of St. Andrews Fernando Castor Filho, UFPE Fernando Quintão Pereira, UFMG Francisco Heron de Carvalho Junior, UFC Hans-Wofgang Loidl, Heriot-Watt University Jeremy Singer, Glasgow University Joao Saraiva, Universidade do Minho João F. Ferreira, Teesside University Lucilia Figueiredo, UFOP Luis Soares Barbosa, Univ. do Minho Manuel António Martins, Univ. de Aveiro Marcelo A. Maia, UFU Marcello Bonsangue, Leiden Univ/CWI Marcelo d'Amorim, UFPE Marco Tulio Valente, UFMG Mariza A. S. Bigonha, UFMG Martin A. Musicante, UFRN Noemi Rodriguez, PUC-Rio Peter Mosses, Swansea University Phil Trinder, Glasgow University (co-chair) Qiu Zongyang, Beijing University Rafael Dueire Lins, UFPE Renato Cerqueira, PUC-Rio Ricardo Massa, UFPE Roberto S. Bigonha, UFMG Roberto Ierusalimschy, PUC-Rio Sandro Rigo, UNICAMP Sergio Soares, UFPE Simon Thompson, Univ. of Kent Varmo Vene, Univ. de Tartu

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cabal-dev add-source
by JP Moresmau 08 Feb '13

08 Feb '13

Hello, I'm trying to understand cabal-dev, and I seem to be missing some basic point, because I can't get dependencies between projects working properly. I have two projects, let's call them P1 and P2. P2 depends on P1, as indicated by its cabal file build-depends field. I run cabal-dev add-source ..\P1 inside P2 then cabal-dev install Everything works fine, and my project compiles, with modules in P2 calling functions from P1. Then I add a new function if an exposed module of P1. I rerun the cabal-dev add-source and cabal-dev install commands to tell P2 of the change, as per the cabal-dev documentation. I change a file in P2 to use the new function, the compilation fails. If I check into the cabal-dev folder, I see the .hi file for my changed module has not been updated (old date). What am I missing? Thanks -- JP Moresmau http://jpmoresmau.blogspot.com/

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ICFP 2013: Call for papers
by David Van Horn 08 Feb '13

08 Feb '13

===================================================================== 18th ACM SIGPLAN International Conference on Functional Programming ICFP 2013 Boston, MA, USA, 25-27 September 2013 http://www.icfpconference.org/icfp2013 ===================================================================== Important Dates ~~~~~~~~~~~~~~~ Submissions due: Thursday, 28 March 2013 23:59 UTC-11 (Pago Pago, American Samoa, time) Author response: Wednesday, 22 May 0:00 UTC-11 Friday, 24 May 2013 23:59 UTC-11 Notification: Friday, 7 June 2013 Final copy due: Friday, 5 July 2013 Scope ~~~~~ ICFP 2013 seeks original papers on the art and science of functional programming. Submissions are invited on all topics from principles to practice, from foundations to features, and from abstraction to application. The scope includes all languages that encourage functional programming, including both purely applicative and imperative languages, as well as languages with objects, concurrency, or parallelism. Topics of interest include (but are not limited to): * Language Design: concurrency and distribution; modules; components and composition; metaprogramming; interoperability; type systems; relations to imperative, object-oriented, or logic programming * Implementation: abstract machines; virtual machines; interpretation; compilation; compile-time and run-time optimization; memory management; multi-threading; exploiting parallel hardware; interfaces to foreign functions, services, components, or low-level machine resources * Software-Development Techniques: algorithms and data structures; design patterns; specification; verification; validation; proof assistants; debugging; testing; tracing; profiling * Foundations: formal semantics; lambda calculus; rewriting; type theory; monads; continuations; control; state; effects; program verification; dependent types * Analysis and Transformation: control-flow; data-flow; abstract interpretation; partial evaluation; program calculation * Applications and Domain-Specific Languages: symbolic computing; formal-methods tools; artificial intelligence; systems programming; distributed-systems and web programming; hardware design; databases; XML processing; scientific and numerical computing; graphical user interfaces; multimedia programming; scripting; system administration; security * Education: teaching introductory programming; parallel programming; mathematical proof; algebra * Functional Pearls: elegant, instructive, and fun essays on functional programming * Experience Reports: short papers that provide evidence that functional programming really works or describe obstacles that have kept it from working If you are concerned about the appropriateness of some topic, do not hesitate to contact the program chair. Abbreviated instructions for authors ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ * By Thursday, 28 March 2013, 23:59 UTC-11 (American Samoa time), submit a full paper of at most 12 pages (6 pages for an Experience Report), including bibliography and figures. The deadlines will be strictly enforced and papers exceeding the page limits will be summarily rejected. * Authors have the option to attach supplementary material to a submission, on the understanding that reviewers may choose not to look at it. * Each submission must adhere to SIGPLAN's republication policy, as explained on the web at http://www.acm.org/sigplan/republicationpolicy.htm * Authors of resubmitted (but previously rejected) papers have the option to attach an annotated copy of the reviews of their previous submission(s), explaining how they have addressed these previous reviews in the present submission. If a reviewer identifies him/herself as a reviewer of this previous submission and wishes to see how his/her comments have been addressed, the program chair will communicate to this reviewer the annotated copy of his/her previous review. Otherwise, no reviewer will read the annotated copies of the previous reviews. Overall, a submission will be evaluated according to its relevance, correctness, significance, originality, and clarity. It should explain its contributions in both general and technical terms, clearly identifying what has been accomplished, explaining why it is significant, and comparing it with previous work. The technical content should be accessible to a broad audience. Functional Pearls and Experience Reports are separate categories of papers that need not report original research results and must be marked as such at the time of submission. Detailed guidelines on both categories are on the conference web site. Proceedings will be published by ACM Press. Authors of accepted submissions are expected to transfer the copyright to the ACM. Presentations will be videotaped and released online if the presenter consents. Formatting: Submissions must be in PDF format printable in black and white on US Letter sized paper and interpretable by Ghostscript. Papers must adhere to the standard ACM conference format: two columns, nine-point font on a ten-point baseline, with columns 20pc (3.33in) wide and 54pc (9in) tall, with a column gutter of 2pc (0.33in). A suitable document template for LaTeX is available:http://www.acm.org/sigs/sigplan/authorInformation.htm Submission: Submissions will be accepted on the web athttps://www.easychair.org/conferences/?conf=icfp2013 . Improved versions of a paper may be submitted at any point before the submission deadline using the same web interface. Author response: Authors will have a 72-hour period, starting at 0:00 UTC-11 on Wednesday, 22 May 2013, to read reviews and respond to them. Special Journal Issue: There will be a special issue of the Journal of Functional Programming with papers from ICFP 2013. The program committee will invite the authors of select accepted papers to submit a journal version to this issue. General Chair: Greg Morrisett, Harvard University Program Chair: Tarmo Uustalu, Institute of Cybernetics, Tallinn Program Committee: Thorsten Altenkirch, University of Nottingham Olaf Chitil, University of Kent Silvia Ghilezan, University of Novi Sad Michael Hanus, Christian-Albrechts-Universität zu Kiel Fritz Henglein, University of Copenhagen Mauro Jaskelioff, Universidad Nacional de Rosario Alan Jeffrey, Alcatel-Lucent Bell Labs Shin-ya Katsumata, Kyoto University Shriram Krishnamurthi, Brown University John Launchbury, Galois Ryan Newton, Indiana University Sungwoo Park, Pohang University of Science and Technology Sam Staton, University of Cambridge Nikhil Swamy, Microsoft Research, Redmond, WA Dimitrios Vytiniotis, Microsoft Research, Cambridge

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Extensible Type Unification
by Leon Smith 08 Feb '13

08 Feb '13

I've been toying with some type-level programming ideas I just can't quite make work, and it seems what I really want is a certain kind of type unification. Basically, I'd like to introduce two new kind operators: kind Set as -- a finite set of ground type terms of kind as kind Range as = Range (Set as) (Set as) -- a greatest lower bound and a least upper bound A type expression of kind (Set as) would either be a type variable of kind (Set as), or set of *ground* type terms of kind (as). A type expression of kind (Range as) would be a type variable of kind (Range as), or two type expressions of kind (Set as). To unify ground terms of these types, one would compute as follows: unifySets xs ys | xs == ys = Just xs | otherwise = Nothing unifyRanges (Range glb0 lub0) (Range glb1 lub1) | glb' `subset` lub' = Just (Range glb' lub') | otherwise = Nothing where glb' = glb0 `union` glb1 lub' = lub0 `isect` lub1 I say sets of ground types, because I have no idea what unification between sets of non-ground types would mean, and I really don't need it. Among applications that came to mind, one could use this to create a restricted IO abstraction that could tell you which kinds of actions might be taken (read from mouse, talk to network, etc), and be able to run only those scripts that are restricted to certain resources. Or, one could define a singular GADT that represents messages/events decorated by various categories, and then define functions that only operate on selected categories of messages. E.G. for something vaguely IRC-ish, one could write something like: data EventCategory = Channel | Presence | Information | Conversation data Event :: Range EventCategory -> * where ChanCreate :: ... -> Event (Range (Set '[Channel]) a) ChanJoin :: ... -> Event (Range (Set '[Channel]) a) ChanLeave :: ... -> Event (Range (Set '[Channel]) a) PresAvailable :: ... -> Event (Range (Set '[Presence]) a) PresAway :: ... -> Event (Range (Set '[Presence]) a) WhoisQuery :: ... -> Event (Range (Set '[Information]) a) WhoisResponse :: ... -> Event (Range (Set '[Information]) a) Message :: ... -> Event (Range (Set '[Conversation]) a) And then be able to write functions such as dispatch :: Event (Range a (Set '[Channel, Conversation])) -> IO () dispatch e = case e of ChanCreate{..} -> ... ChanJoin{..} -> ... ChanLeave{..} -> ... Message{..} -> ... In this case, the case analysis tool would be able to warn me if I'm missing any possible events in this dispatcher, or if I have extraneous events that I can't be passed (according to my type.) Anyway, I've been trying to see if I can't come up with something similar using existing type-level functionality in 7.6, with little success. (Though I'm not very experienced with type-level programming.) If not, might it be possible to add some kind of extensible unification mechanism, in furtherance of type-level programming? Best, Leon

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Announce: LA Haskell User Group February Meeting
by Phil Freeman 07 Feb '13

07 Feb '13

Dear Haskellers, There will be a meeting of the LA Haskell User Group on Wednesday February 13th at 7pm. The details, including a list of discussion topics, as they become available, can be found here: http://www.meetup.com/Los-Angeles-Haskell-User-Group/events/102199892/ Thanks, Phil Freeman.

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Either example
by Jacob Thomas 07 Feb '13

07 Feb '13

Hello I'm new to Haskell, and need help with figuring out the Either type... Any example to show how this works? Jacob

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Sol vingt simple problem in various languages and systems
by Doaitse Swierstra 07 Feb '13

07 Feb '13

At https://gist.github.com/ckirkendall/2934374 you find solutions in many languages to a simple programming problem: the evaluation of an expression in an environment. I want to point your attention to the currently last three entries: - one using the UUAGC compiler to solve the problem in an aspect oriented way (entered by Jeroen Bransen (jbransen)) - one using some Haskell features, libraries and extensions (entered by me (doaitse)) - one using our attribute grammar combinators from the AspectAG package, which expresses the various aspects in an attribute grammar style (entered by Marcos Viera (marcosomarviera)) In case you did not manage to avoid getting wound up in a discussion about programming languages you can find ammunition here. Doaitse

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GHCi (7.4.2) is working on ARM
by kenny lu 07 Feb '13

07 Feb '13

I've got a Cubieboard a few weeks back. I started it off with Linaro (Ubuntu) 12.06. Today I started to upgrade the OS to 12.11, which surprisingly came with ghc 7.4.2. And ghci magically works too. Here are the links http://www.cubieboard.org sudo apt-get install update-manager-core sudo apt-get update sudo apt-get upgrade sudo do-release-upgrade Regards, Kenny

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Haskell Weekly News: Issue 257
by Daniel Santa Cruz 07 Feb '13

07 Feb '13

Welcome to issue 257 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of January 27 to February 02, 2013. Quotes of the Week * shachaf: Everyone forgets about Agda Lovelace, the first constructivist. * applicative: I have my new ghc and am reinstalling my feeble world * wuttf: My world is starting to feel like isToyLanguage x = x /= Haskell * PenguinOfDoom: Being enlightened gentlemen, we split all programming languages into two groups, sucks and doesn't-suck and put all of them into the first group. * Taneb: lens has got to be the only library with more contributors than people who know how it works * shachaf: I like to put all my application's modules under GHC.* That's because I use the GHC API, and I want them not to conflict. Top Reddit Stories * The FP Complete School of Haskell goes beta Domain: fpcomplete.com, Score: 84, Comments: 45 On Reddit: [1] http://goo.gl/dEEyU Original: [2] http://goo.gl/0eKLt * My reaction to: How To Exclude Women From Your Technical Community: A Tutorial Domain: self.haskell, Score: 75, Comments: 145 On Reddit: [3] http://goo.gl/dVnVv Original: [4] http://goo.gl/dVnVv * Edward Yang: The GHC scheduler Domain: blog.ezyang.com, Score: 72, Comments: 1 On Reddit: [5] http://goo.gl/pkCmD Original: [6] http://goo.gl/SP1s3 * GHC HEAD now has support for named holes; an extension of -XTypeHoles. Feedback welcome! Domain: github.com, Score: 44, Comments: 32 On Reddit: [7] http://goo.gl/87Pbw Original: [8] http://goo.gl/cqX9N * LiquidHaskell - Safely Catching A List By Its Tail Domain: goto.ucsd.edu, Score: 44, Comments: 2 On Reddit: [9] http://goo.gl/uxU64 Original: [10] http://goo.gl/9aS35 * ProseDoc: A literate programming tool for Haskell inspired by docco Domain: shangaslammi.github.com, Score: 43, Comments: 12 On Reddit: [11] http://goo.gl/x4YGE Original: [12] http://goo.gl/sM4bN * ANNOUNCE: GHC version 7.6.2 Domain: haskell.org, Score: 39, Comments: 16 On Reddit: [13] http://goo.gl/BS6Sm Original: [14] http://goo.gl/RPF00 * What you consider "advanced" Haskell topics? Domain: self.haskell, Score: 34, Comments: 45 On Reddit: [15] http://goo.gl/JRgzG Original: [16] http://goo.gl/JRgzG * How to write unmaintainable Haskell code Domain: github.com, Score: 34, Comments: 49 On Reddit: [17] http://goo.gl/V0nxC Original: [18] http://goo.gl/G8wNv * Introduction to Haskell, Lecture 3 is Live (Types and Typeclasses) Domain: shuklan.com, Score: 32, Comments: 5 On Reddit: [19] http://goo.gl/JyH81 Original: [20] http://goo.gl/bve7N * Proposal: A trivial Cabal package signing utility for use with Hackage Domain: github.com, Score: 32, Comments: 61 On Reddit: [21] http://goo.gl/R2l9g Original: [22] http://goo.gl/IpYSo Top StackOverflow Questions * Haskell/GHC UndecidableInstances - example for non-terminating type check? votes: 19, answers: 2 Read on SO: [23] http://goo.gl/KX8oj * Efficient parallel strategies votes: 15, answers: 2 Read on SO: [24] http://goo.gl/aDnW2 * Is it possible to implement MonadFix for `Free`? votes: 15, answers: 2 Read on SO: [25] http://goo.gl/uKOrO * Do Haskell imports have side effects? votes: 15, answers: 1 Read on SO: [26] http://goo.gl/sjltX * What monads can be expressed as Free over some functor? votes: 10, answers: 1 Read on SO: [27] http://goo.gl/Q8MF9 * What is the point of having a lazy/strict version of Writer? votes: 10, answers: 1 Read on SO: [28] http://goo.gl/InUsm * Why can applicative functors have side effects, but functors can't? votes: 9, answers: 4 Read on SO: [29] http://goo.gl/LxUi5 * How to write fixed point build rules in Shake, e.g. Latex votes: 9, answers: 1 Read on SO: [30] http://goo.gl/Ef82G * Event handling in Netwire compared to conventional FRP frameworks votes: 9, answers: 2 Read on SO: [31] http://goo.gl/mA4Kc Until next time, Daniel Santa Cruz References 1. http://fpcomplete.com/school-of-haskell-goes-beta/ 2. http://www.reddit.com/r/haskell/comments/17ngtq/the_fp_complete_school_of_h… 3. http://www.reddit.com/r/haskell/comments/17jy0e/my_reaction_to_how_to_exclu… 4. http://www.reddit.com/r/haskell/comments/17jy0e/my_reaction_to_how_to_exclu… 5. http://blog.ezyang.com/2013/01/the-ghc-scheduler/ 6. http://www.reddit.com/r/haskell/comments/17fd8c/edward_yang_the_ghc_schedul… 7. https://github.com/ghc/ghc/commit/677144b858f4a425e77399bdfbfcd43dbabd1488 8. http://www.reddit.com/r/haskell/comments/17l9xm/ghc_head_now_has_support_fo… 9. http://goto.ucsd.edu/~rjhala/liquid/haskell/blog/blog/2013/01/31/safely-cat… 10. http://www.reddit.com/r/haskell/comments/17ohbm/liquidhaskell_safely_catchi… 11. http://shangaslammi.github.com/prose-doc/ 12. http://www.reddit.com/r/haskell/comments/17keu0/prosedoc_a_literate_program… 13. http://www.haskell.org/pipermail/glasgow-haskell-users/2013-January/023661.… 14. http://www.reddit.com/r/haskell/comments/17jyw9/announce_ghc_version_762/ 15. http://www.reddit.com/r/haskell/comments/17gavl/what_you_consider_advanced_… 16. http://www.reddit.com/r/haskell/comments/17gavl/what_you_consider_advanced_… 17. https://github.com/quchen/unmaintainable_haskell/blob/master/README.md 18. http://www.reddit.com/r/haskell/comments/17idma/how_to_write_unmaintainable… 19. http://shuklan.com/haskell/lec03.html 20. http://www.reddit.com/r/haskell/comments/17ic23/introduction_to_haskell_lec… 21. https://github.com/chrisdone/cabal-sign 22. http://www.reddit.com/r/haskell/comments/17njda/proposal_a_trivial_cabal_pa… 23. http://stackoverflow.com/questions/14661073/haskell-ghc-undecidableinstance… 24. http://stackoverflow.com/questions/14624376/efficient-parallel-strategies 25. http://stackoverflow.com/questions/14636048/is-it-possible-to-implement-mon… 26. http://stackoverflow.com/questions/14666666/do-haskell-imports-have-side-ef… 27. http://stackoverflow.com/questions/14641864/what-monads-can-be-expressed-as… 28. http://stackoverflow.com/questions/14644830/what-is-the-point-of-having-a-l… 29. http://stackoverflow.com/questions/14576543/why-can-applicative-functors-ha… 30. http://stackoverflow.com/questions/14622169/how-to-write-fixed-point-build-… 31. http://stackoverflow.com/questions/14654385/event-handling-in-netwire-compa… 32. https://plus.google.com/105107667630152149014/about

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