November 2011 - Haskell-Cafe

PADL 2012 Call for Participation
by Claudio Russo 28 Nov '11

28 Nov '11

Call for Participation ====================== 14th International Symposium on Practical Aspects of Declarative Languages (PADL 2012) http://research.microsoft.com/~crusso/padl12 Philadelphia, Pennsylvania, USA, January 23-24, 2012 Co-located with ACM POPL'12 You are cordially invited to PADL'12. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including functional, logic and constraints. PADL'12 is sponsored by Association for Logic Programming with cooperation of ACM SIGPLAN and support by Microsoft Research. Registration ============ To register for PADL'12, please follow the instructions at: https://regmaster3.com/2012conf/POPL12/register.php The early registration deadline is December 24, 2011. The registration fee will cover a copy of the symposium proceedings, refreshments, and an informal dinner. Hotel Information ================= PADL 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 ======= The symposium will include invited talks by Boon Thau Loo and Don Stewart, and 19 technical papers selected from 41 submissions. The preliminary program is as follows: Invited Talk (9:00-10:00) * Boon Thau Loo Recent Advances in Declarative Networking Break (10:00-10:30) Session 1: Applications (10:30-12:00) * Mayer Goldberg and Guy Wiener A Declarative Approach for Software Modeling * Sergio Antoy and Michael Hanus Contracts and Specifications for Functional Logic Programming * Pedro M. Martins, Julie A. McCann and Susan Eisenbach The Environment as an Argument Lunch (not provided) (12:00-13:30) Session 2: Logic Programming (13:30-15:30) * Yuliya Lierler, Shaden Smith, Mirek Truszczynski and Alex Westlund Weighted-Sequence Problem: ASP vs CASP and Declarative vs Problem-Oriented Solving * Marcello Balduccini and Yuliya Lierler Practical and Methodological Aspects of the Use of Cutting-Edge ASP Tools * Christian Theil Have and Henning Christiansen Efficient tabling of structured data using indexing and program transformation * Dario Campagna, Beata Sarna-Starosta and Tom Schrijvers Optimizing Inequality Joins in Datalog with Approximated Constraint Propagation Break (15:30-16:00) Session 3: Parallelism and Concurrency (16:00-17:30) * Elvira Albert, Puri Arenas and Miguel Gomez-Zamalloa Symbolic Execution of Concurrent Objects in CLP * Pablo Chico De GuzmÃ¡n, Amadeo Casas, Manuel Carro and Manuel Hermenegildo A Segment-Swapping Approach for Executing Trapped Computations * Michael Lesniak Palovca: Describing and Executing Graph Algorithms in Haskell Informal PADL Dinner (Place: TBA) Tuesday, January 24, 2012 Breakfast (8:00-9:00) Invited Talk (9:00-10:00) * Don Stewart Make Things Now! Pragmatic Functional Programming in Haskell Break (10:00-10:30) Session 4: Domain Specific Languages I (10:30-12:00) * Kenny Zhu, Kathleen Fisher and David Walker LearnPADS++: Incremental Inference of Ad Hoc Data Formats * Jeroen Bransen, Arie Middelkoop, Atze Dijkstra and S. Doaitse Swierstra The Kennedy-Warren algorithm revisited: ordering Attribute Grammars * Nicholas Coleman Distributed Policy Specification and Interpretation with Classified Advertisements Lunch (not provided) (12:00-13:30) Session 5: Domain Specific Languages II (13:30-15:30) * Andy Gill and Bowe Neuenschwander Handshaking in Kansas Lava using Patch Logic * Daniel Winograd-Cort, Hai Liu and Paul Hudak Virtualizing Real-World Objects in FRP * Edwin Brady and Kevin Hammond Resource-safe Systems Programming with Embedded Domain Specific Languages * David Broman and Henrik Nilsson Node-Based Connection Semantics for Equation-Based Object-Oriented Modeling Languages Break (15:30-16:00) Session 6: Numerics (16:00-17:00) * Paul Tarau A Declarative Specification of Tree-based Symbolic Arithmetic Computations * Vincent St-Amour, Sam Tobin-Hochstadt, Matthew Flatt and Matthias Felleisen Typing the Numeric Tower

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Proposed change to mime-mail
by Erik Hesselink 28 Nov '11

28 Nov '11

Hi all, I've found and solved a problem with mime-mail, and Michael Snoyman asked me to send a request for feedback to -cafe, so here goes. In short, the issue is with address headers containing 'special' (non-ascii) characters. In mime-mail, these are automatically encoded according to RFC 2047. However, the email address part of an address header is not allowed to be encoded. My patch adds 'from', 'to', 'cc' and 'bcc' fields to the Mail data type, and creates correct headers from these fields. This does make the Mail type a bit larger, so I've also added a smart constructor with initializes these fields with empty lists (only 'from' is required). For more details, see my initial bug report [1] and my patches in the pull request [2]. If you have any comments on this change, please let me know. Regards, Erik [1] https://github.com/snoyberg/mime-mail/issues/5 [2] https://github.com/snoyberg/mime-mail/pull/6

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Reminder Haskell Munich
by Heinrich Hördegen 28 Nov '11

28 Nov '11

Dear all, just a reminder for our monthly Haskell get-together in Munich, Cafe Puck, tomorrow (Tuesday, 29th, 19h30). If you will join and didn't already click the button, you can do it here: http://www.haskell-munich.de/dates Have a nice day, Heinrich -- -- hoerdegen(a)funktional.info www.funktional.info --

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Haskellers.com polls (specifically, the mascot question)
by Michael Snoyman 28 Nov '11

28 Nov '11

Hi all, I've just added the polls feature to Haskellers.com, and created an initial poll about mascots[1]. Let me know if there are any issues. Michael PS: I've also added Google+ profile link support, just go to your edit profile page and paste in the link. [1] http://www.haskellers.com/poll/1

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Mascot Poll Results
by heathmatlock 27 Nov '11

27 Nov '11

Haskellers.com poll: Yes 52 votes (50%), 22 verified votes (53%) No 51 votes (49%), 19 verified votes (46%) Email: Yes 14 (64%) No 8 (36%) Seems a bit divided. -- Heath Matlock +1 256 274 4225

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Current Haskell report URL
by Tom Murphy 27 Nov '11

27 Nov '11

Is there a reason that the Haskell 2010 report is in a subdirectory of haskell.org/onlinereport (which currently points to the Haskell98 standard)? http://www.haskell.org/onlinereport/ -- Haskell98 http://www.haskell.org/onlinereport/haskell2010/ -- Haskell2010 If it's for historical reasons - because books etc. use this URL for the 98 standard, then I'd highly recommend making a new directory called "currentreport" or something (if there isn't one already). The current impression that we give is that Haskell98 is the current standard, and Haskell2010 isn't compiler-supported. amindfv / Tom

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ANNOUNCE: clientsession-0.7.3.4 (performance enhancement)
by Michael Snoyman 27 Nov '11

27 Nov '11

Hi all, tl;dr: randomIV is now much faster, API is the same, upgrade ASAP to avoid painful slowdowns. Version 0.7 of clientsession brought with it a much enhanced encryption and hashing algorithm, courtesy of Felipe Lessa. Beginning with this version, you now need to provide an Initialization Vector (IV) for encrypting cookies, and these IVs need to be randomly generated. To start off with, we simply used the getIVIO[1] function to generate these values. Recently, some Yesod users reported that version 0.9 of Yesod no longer lived up to previous benchmarks. After some research, I determined that the slowdown came from the call to randomIV in clientsession. The initial fix was simply to disable this call when it wasn't used, but it was still a significant slowdown for most users of Yesod. Over the past few days, Felipe and I put together a significantly more efficient version of randomIV. getIVIO simply opens up /dev/urandom on each request, which involves I/O. As a result, the average run time of the function in our testing was 1.686ms. Instead, our new code initializes with a call to /dev/urandom for the base randomness. It then uses AES encryption to work as a cryptographic random number generator for generating successive IVs. Additionally, every 1000 calls (we'll probably change that number over time), it spawns a new thread to reseed the generator from /dev/urandom again. The result is a function that takes 7.144764 us, aka 236 times faster. Thanks for the initial reporters who commented on the slowdown in Yesod. If you install the newest clientsession and rerun the benchmarks, you should see *significantly* better results. Michael [1] http://hackage.haskell.org/packages/archive/crypto-api/0.8/doc/html/Crypto-…

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XML modification
by Andrew Coppin 25 Nov '11

25 Nov '11

Hi guys. I've got a folder with about 80 XML files in it. I want to take each file and make specific modifications to it. (Mostly just finding specific attributes and changing their values to make then all consistent.) Now I guess it wouldn't take me /that/ long to code something from scratch. But does anybody have a better suggestion for tools or libraries that might be useful?

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blaze-textual-native and aeson-native are being deprecated
by Michael Snoyman 25 Nov '11

25 Nov '11

Hi all, In the last Yesod release, we created two new packages: blaze-textual-native and aeson-native. These were direct forks of their source packages, with just two changes: blaze-textual-native did not include a double-conversion dependency, and aeson-native depended on blaze-textual-native instead of blaze-textual. The reason for all this is that there is a GHC bug which prevents C++ code from working correctly with GHCi and Template Haskell[1]. Bryan recently released a new version of blaze-textual which no longer uses double-conversion by default (it's still available with compile-time flags if you want the extra speed and don't need TH/GHCi), and as a result, we are very happy to be deprecating the native siblings. Fortunately, there are not that many packages on Hackage using these libraries; in fact, the only packages for which I'm not a maintainer are dingo-core, dingo-widgets and hledger-web. However, since these are Yesod dependencies, I'm guessing many Yesod users reference aeson-native in their site cabal files. Technically speaking, switching from aeson-native to aeson in a library should constitute a major version bump. However, in this case, I think we want these deprecated packages to die as quickly as possible. So my plan is to switch all of my packages from using aeson-native to aeson some time next week. The result will likely be broken builds for some people; all you'll need to do is edit your cabal file and replace aeson-native with aeson (likewise for blaze-textual). Are there any objections to this course of action, or better ideas on how to handle the situation? Michael [1] Please don't ask me for details, I don't know them. And for all I know, the bug has already be fixed in newer GHCs.

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FGL custom node identification (Label -> Node lookup)
by Thomas DuBuisson 24 Nov '11

24 Nov '11

All, The containers library has a somewhat primitive but certainly useful Data.Graph library. Building a graph with this library simultaneously results in the lookup functions: m1 :: Vertex -> (node, key, [key]) m2 :: key -> Maybe Vertex (where 'key' is like FGL's 'label' but is assumed to be unique) This is exactly what I wanted when building and analyzing a call graph in FGL. To that end, I started making a graph type that tracked label to Node mappings, wrapping Data.Graph.Inductive.Gr, and assuming the labels are all unique. The classes for such a graph actually aren't possible. The ability to build a mapping from a node's 'label' to the 'Node' requires extra context (ex: Hashable, Ord, or at least Eq), but such context can not be provided due to the typeclass construction. Is there any chance we can change the Graph and DiaGraph classes to expose the type variables 'a' and 'b'? class Graph gr a b where ... class (Graph gr) => DynGraph gr a b where ... This would allow instances to provide the needed context: instance (Hashable a, Hashable b) => Graph UniqueLabel a b where ... buildGraph = ... some use of containers libraries that require context ... ... lookupNode :: Hashable a => UniqueLabel a b -> a -> Node -- etc Cheers, Thomas P.S. Please do educate me if I simply missed or misunderstood some feature of FGL.

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