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Haskell Weekly News: Issue 215
by Daniel Santa Cruz 16 Feb '12

16 Feb '12

Welcome to issue 215 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of February 5 to 11, 2012. You can find the HTML version of this issue at: http://contemplatecode.blogspot.com/2012/02/haskell-weekly-news-issue-215.h… Quotes of the Week * nand': haskell has a few advantages in the industry that few other languages can offer. these will become more obvious as time goes on and programming is forced into a functional direction in general. * seo: What i do not realize is actually how you are now not really much more well-liked than you might be right now. You are so intelligent. You realize thus significantly in terms of this subject, produced me in my view consider it from so many numerous angles. Its like men and women are not interested unless it‚s one thing to do with Woman gaga! Your personal stuffs excellent. Always care for it up! * monochrom: Schrodinger's Klein glass bottle: before you look, the cat is inside or outside; after you look, it is inside and outside :) * cmccann: Ruby is a fine language if you're secretly a lisp programmer but want to hide behing perl and smalltalk so nobody catches you * mlh: nice quote -- quick, someone register it for posterity * something: somebody never said, naturally. * irene-knapp: I was going to take a famous quote and put it in lambdabot as my own but I couldn't decide on one * shachaf: getLine :: IO String contains a String in the same way that /bin/ls contains a list of files * edwardk: [unsafePerformIO] sounds like a good idea, its tempting, it makes life easy, for the first 2 lines of code. then you go to write the third and everything goes to shit * cmccann: Idiom brackets are where you consume a mixture of alcohol and Conor McBride papers until your vision gets blurry enough that you can't actually see the Applicative operators anymore. * Philippa: incidentally, if you think about this you're probably starting to image control flow that looks like it's a glyph for summoning cthulhu - and then realising that it's 3d and consists of 'towers'. Make sense? * c_wraith: also, "actual" reals is a funny thing to call a set that consists mostly of things that cannot be described. * NihilistDandy: I feel like a hipster whenever I talk programming with people at my school. I always have to preface discussions with "you've probably never heard of it" :/ * ion: Three lefts make two wrongs * elliott: Explicit recursion should generally be avoided. Also, general recursion should be explicitly avoided! * CodeWeaverX: I expect that Weird Untraceable Suitcases Full Of Bad could result from the program assuming such an operation is pure when it clearly isn't. * elliott: cmccann: the instances list haddock generates is now a thing of majesty edwardk: elliott: welcome to my world * mzero: functional programming has a property that is often lacking in other languages... at dinner last night we were discussing it, and I dubbed it: "The Princess Bride" property --- which is, that a piece of code means what you think it means * sclv: You have a problem and think "I'll use a hash function." Now you have intermittantly colliding problems. * monochrom: data Ph a = Ph -- the phantom monad ksion: Is that a new Star Wars prequel? ;) * user1151874: i already declare hp as int with value 3 now my problem is when i put "hp--", it shows error [...] but if i put "--hp", the result print is 3 not 2. * edwardk: thats my secret. really i don't write anything. i just let others do the work and upload it to hackage behind their backs Top Reddit Stories * Haskell as most mainstream non-mainstream language? The RedMonk Programming Language Rankings: February 2012 Domain: redmonk.com, Score: 45, Comments: 25 On Reddit: [1] http://goo.gl/xWHB8 Original: [2] http://goo.gl/REBXN * The future is parallel, and the future of parallel is declarative (Simon Peyton Jones) [RE: Escape From the Ivory Tower] Domain: yow.eventer.com, Score: 41, Comments: 5 On Reddit: [3] http://goo.gl/PJSlh Original: [4] http://goo.gl/zUKT5 * How Prelude avoids overlapping instances in Show Domain: brandon.si, Score: 32, Comments: 18 On Reddit: [5] http://goo.gl/qGPZK Original: [6] http://goo.gl/rC6qr * InfoQ: Yesod Web Framework (Michael's QCon talk) Domain: infoq.com, Score: 32, Comments: 12 On Reddit: [7] http://goo.gl/93SFv Original: [8] http://goo.gl/Xao7S * Search tree that does not require that items be sorted. Domain: twanvl.nl, Score: 28, Comments: 3 On Reddit: [9] http://goo.gl/R2yLD Original: [10] http://goo.gl/WGfcV * Reverse engineering the ZeroMQ wire protocol for ZMQHS Domain: xrl.tureus.com, Score: 27, Comments: 0 On Reddit: [11] http://goo.gl/UKIun Original: [12] http://goo.gl/oVstA * Announcing Yesod 0.10 - conduits, persistent 0.8, improved Coffeescript integration Domain: yesodweb.com, Score: 25, Comments: 12 On Reddit: [13] http://goo.gl/1RRJH Original: [14] http://goo.gl/KftN5 * Real World Haskell book site -- is it known to be down? If so how long has it been down and will it come back? Domain: book.realworldhaskell.org, Score: 24, Comments: 15 On Reddit: [15] http://goo.gl/GV6z2 Original: [16] http://goo.gl/RCxnT * What do Haskellers think of Rust? It's got lambdas and ADTs with C-style notation. Domain: rust-lang.org, Score: 24, Comments: 40 On Reddit: [17] http://goo.gl/a9bCB Original: [18] http://goo.gl/xAKHx * r/darcs - for discussing darcs and patch theory Domain: reddit.com, Score: 24, Comments: 8 On Reddit: [19] http://goo.gl/37ArD Original: [20] http://goo.gl/qQiaD * Will Haskell be the Smalltalk of functional programming? Domain: self.haskell, Score: 22, Comments: 54 On Reddit: [21] http://goo.gl/ZxmBN Original: [22] http://goo.gl/ZxmBN Top StackOverflow Questions * Abusing the algebra of algebraic data types - why does this work? votes: 53, answers: 4 Read on SO: [23] http://goo.gl/MyQRO * Recommended reading/tutorials to understand reactive-banana FRP library votes: 13, answers: 3 Read on SO: [24] http://goo.gl/hTPv6 * Safe modelling of relational data in Haskell votes: 12, answers: 2 Read on SO: [25] http://goo.gl/4bEXX * What are the definitions for >>= and return for the IO monad? votes: 12, answers: 3 Read on SO: [26] http://goo.gl/9jH2x * Basic Structure of a Haskell Program votes: 11, answers: 1 Read on SO: [27] http://goo.gl/3OcKg * GHC API - How to dynamically load Haskell code from a compiled module using GHC 7.2? votes: 11, answers: 2 Read on SO: [28] http://goo.gl/aYKZz * Lifting a higher order function in Haskell votes: 9, answers: 1 Read on SO: [29] http://goo.gl/JhmjK * How do you check the type of a local variable? votes: 8, answers: 5 Read on SO: [30] http://goo.gl/Ynfgv * Tail optimization guarantee - loop encoding in Haskell votes: 7, answers: 2 Read on SO: [31] http://goo.gl/PKqfq * Writing in pointfree style f x = g x x votes: 7, answers: 1 Read on SO: [32] http://goo.gl/EIFBw Until next time, Daniel Santa Cruz References 1. http://redmonk.com/sogrady/2012/02/08/language-rankings-2-2012/ 2. http://www.reddit.com/r/haskell/comments/ph4uq/haskell_as_most_mainstream_n… 3. http://yow.eventer.com/events/1004/talks/1055 4. http://www.reddit.com/r/haskell/comments/phnd3/the_future_is_parallel_and_t… 5. http://brandon.si/code/how-the-haskell-prelude-avoids-overlapping-types-in-… 6. http://www.reddit.com/r/haskell/comments/pel34/how_prelude_avoids_overlappi… 7. http://www.infoq.com/presentations/Yesod 8. http://www.reddit.com/r/haskell/comments/pjqpr/infoq_yesod_web_framework_mi… 9. http://twanvl.nl/blog/haskell/SemilatticeSearchTree 10. http://www.reddit.com/r/haskell/comments/pj6n7/search_tree_that_does_not_re… 11. http://xrl.tureus.com/black-box-reverse-engineering-zmq 12. http://www.reddit.com/r/haskell/comments/pcojs/reverse_engineering_the_zero… 13. http://www.yesodweb.com/blog/2012/02/release-0-10 14. http://www.reddit.com/r/haskell/comments/phxjo/announcing_yesod_010_conduit… 15. http://book.realworldhaskell.org/read 16. http://www.reddit.com/r/haskell/comments/pd79r/real_world_haskell_book_site… 17. http://www.rust-lang.org/ 18. http://www.reddit.com/r/haskell/comments/pewtc/what_do_haskellers_think_of_… 19. http://reddit.com/r/darcs 20. http://www.reddit.com/r/haskell/comments/pkv8g/rdarcs_for_discussing_darcs_… 21. http://www.reddit.com/r/haskell/comments/pczyz/will_haskell_be_the_smalltal… 22. http://www.reddit.com/r/haskell/comments/pczyz/will_haskell_be_the_smalltal… 23. http://stackoverflow.com/questions/9190352/abusing-the-algebra-of-algebraic… 24. http://stackoverflow.com/questions/9210412/recommended-reading-tutorials-to… 25. http://stackoverflow.com/questions/9234205/safe-modelling-of-relational-dat… 26. http://stackoverflow.com/questions/9244538/what-are-the-definitions-for-and… 27. http://stackoverflow.com/questions/9153574/basic-structure-of-a-haskell-pro… 28. http://stackoverflow.com/questions/9198140/ghc-api-how-to-dynamically-load-… 29. http://stackoverflow.com/questions/9243215/lifting-a-higher-order-function-… 30. http://stackoverflow.com/questions/9210311/how-do-you-check-the-type-of-a-l… 31. http://stackoverflow.com/questions/9149183/tail-optimization-guarantee-loop… 32. http://stackoverflow.com/questions/9169046/writing-in-pointfree-style-f-x-g…

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GHC -WAll, -fwarn-unused-do-bind and Cabal
by JP Moresmau 15 Feb '12

15 Feb '12

I'm confused: I'm using GHC 7.0.2 and Cabal 1.10.1.0 with cabal-install 0.10.2. I use -Wall in my Cabal file. If I build a Haskell file with unused do binds, via the GHC API I get no warning, which is normal, since the doc states: The warnings that are not enabled by -Wall are ..., -fwarn-unused-do-bind .... But if I build my project through cabal it gives me the warning! Why is compiling with Cabal giving that extra warning that GHC on its own with the same flags doesn't give? Using --verbose on cabal build does not give any clue, no suspicious extra flag is passed on. Any pointer appreciated! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Optimizations and parallel execution in the IO for a small spellchecker
by Paul Sujkov 15 Feb '12

15 Feb '12

Hi everyone, http://hpaste.org/63732 that's a very simple spellchecker application: it consumes standard Linux dictionary, reads a file, and prints out words from that file that are not on the dictionary. I have taken it from a little cross-language benchmark and used to benchmark existing hash table implementations available on Hackage (with one used in code being the best according to timings). The question is: can I go further and effectively execute lookup and (maybe) output (line 20 or line 26 in the snippet) in parallel? I'm not good at all with Haskell parallel packages; I've tried monad-parallel (naive implementation eats away all the memory available) and parallel (haven't tried Par monad yet), but the last dosn't seem to fit well with the IO operations. If anyone can give me any suggestions on how can I implement parallel execution, or any thoughts on further sequential optimizations, it would be deeply appreciated. -- Regards, Paul Sujkov

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Concurrency strategy for 2 threads and rare events
by JP Moresmau 15 Feb '12

15 Feb '12

Hello, I'm wondering what's the best strategy to use in the following scenario: - 2 threads - One perform some work that will take time, possibly go on forever - Another waits for user input (like commands from the keyboard) that affects thread 1 (causing it to stop, in the simplest case) I've read a bit on MVar and channels, but they seem to be a lot for cases where the reading thread block for input. In my case, I expect to have "something" that thread 2 updates when an event occur, and thread 1 checks it regularly. So thread 1 should not block, but should check "is there something" and there is, act on it, otherwise continue doing what it was currently doing. I suppose I could just tryTakeMVar on a MVar, but is there something more adapted to my needs? Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

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Re: [Haskell-cafe] Hackage 2 maintainership
by Duncan Coutts 15 Feb '12

15 Feb '12

On 14 February 2012 10:43, Kirill Zaborsky <qrilka(a)gmail.com> wrote: > I apologize, > But does hackage.haskell.org being down for some hours already has something > with the process of bringing up Hackage 2? No, completely independent. The server was down for a few hours (and I think restored in the morning by the sysadmin at Galois). It was while I was mirroring to the new test server, but I don't think that was the cause of the outage. Some people were joking that the old server didn't want to be retired and so was shutting down to prevent the mirroring :-) Duncan

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[haskell-cafe] Some reflections on Haskell
by Doug McIlroy 15 Feb '12

15 Feb '12

Markus: "What about hoogle/hayoo and hackage?" Antoine: "Do you have any links to examples that we should imitate?" Hackage is notionally similar to the Java API documentation at http://www.oracle.com/technetwork/java/javase/documentation/ But Hackage "Documentation" pages typically only give syntax, while Java pages invariably summarize semantics. This makes a world of difference. The quality of the summaries bespeaks a lot of editorial attention above and beyond culling annotations from source code. Considerable care has been taken in describing the GHC library at http://www.haskell.org/ghc/docs/ but even there one can find absolute mystery entries like http://www.haskell.org/ghc/docs/latest/html/libraries/haskell98-2.0.0.1/Loc… Doug > It is hard to find one's way in this ecosystm. It needn't be, > as Java illustrates. To my mind Java's great contribution to the > world is its library index--light years ahead of typical > "documentation" one finds at haskell.org, which lacks the guiding > hand of a flesh-and-blood librarian. In this matter, it > seems, industrial curation can achieve clarity more easily than > open source.

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Language Shootout
by Louis Wasserman 15 Feb '12

15 Feb '12

Out of curiosity, do we know why the Language Shootout has upgraded<http://shootout.alioth.debian.org/u64q/program.php?test=spectralnorm&lang=g…>to GHC 7.4.1, but still isn't using -fllvm for e.g. the spectral-norm benchmark? (It results in a nonnegligible speedup on my machine.) Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

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Google Summer of Code 2012 Announced
by Johan Tibell 14 Feb '12

14 Feb '12

Hi all, Here's a heads-up that this year's Google of Code is kicking off. My experience from the last few years is that we can maximize the output we get from GSoC by being proactive and writing down semi-detailed explanations of what kind of projects we'd like to see, instead of letting the students pick themselves*. Here's three examples of such write-ups I did last year: http://blog.johantibell.com/2011/03/summer-of-code-project-suggestions.html Concretely: 1. Write down the project suggestions somewhere (e.g. on the wiki, your blog, etc). 2. Advertise the projects on haskell-cafe, reddit, twitter, Google+ 3. Profit. * The students tend to not know what makes a good GSoC project and often aim for something too difficult, like writing a new project from scratch instead of contributing to an old one. Contributing to widely used libraries or infrastructure usually results in * a larger benefit for the community, and * the students sticking around. My guess is that the student tend to stick around after the project is done if they contribute to infrastructure projects, as they'll see their stuff get used and will get feature requests/bug reports that will make them continue working on the project. -- Johan ---------- Forwarded message ---------- From: Carol Smith <carols(a)google.com> Date: Sat, Feb 4, 2012 at 8:43 AM Subject: Google Summer of Code 2012 Announced To: Google Summer of Code Announce < google-summer-of-code-announce(a)googlegroups.com> Hi all, We're pleased to announce that Google Summer of Code will be happening for its eighth year this year. Please check out the blog post [1] about the program and read the FAQs [2] and Timeline [3] on Melange for more information. [1] - http://google-opensource.blogspot.com/2012/02/google-summer-of-code-2012-is… [2] - http://www.google-melange.com/gsoc/document/show/gsoc_program/google/gsoc20… [3] - http://www.google-melange.com/gsoc/events/google/gsoc2012 Cheers, Carol -- You received this message because you are subscribed to the Google Groups "Google Summer of Code Announce" group. To post to this group, send email to google-summer-of-code-announce(a)googlegroups.com. To unsubscribe from this group, send email to google-summer-of-code-announce%2Bunsubscribe(a)googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-summer-of-code-announce?hl=en.

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Building a Haskell project which depends on an old version of base
by Steven J. Murdoch 14 Feb '12

14 Feb '12

I'm trying to build a Haskell project[1] which appears to be dependent on an function in a old version of base (GHC.Handle.fillReadBuffer). I've downgraded to Haskell platform 2010.2.0.0 which comes with GHC 6.12.3 (installed by homebrew on MacOS X 10.6.8), and ghc-pkg appears to indicate the backwards compatible library for base is available: $ ghc-pkg list base /Users/ghc6/homebrew/Cellar/ghc/6.12.3/lib/ghc/package.conf.d base-3.0.3.2 base-4.2.0.2 /Users/ghc6/.ghc/i386-darwin-6.12.3/package.conf.d However, when I try to cabal build the package, I get the following error: $ cabal -v build Creating dist/build (and its parents) Creating dist/build/autogen (and its parents) Preprocessing executables for TorDNSEL-0.1.1... Building TorDNSEL-0.1.1... Building executable tordnsel... Creating dist/build/tordnsel (and its parents) Creating dist/build/tordnsel/tordnsel-tmp (and its parents) /Users/ghc6/homebrew/bin/ghc --make -o dist/build/tordnsel/tordnsel -hide-all-packages -fbuilding-cabal-package -package-conf dist/package.conf.inplace -i -idist/build/tordnsel/tordnsel-tmp -isrc -idist/build/autogen -Idist/build/autogen -Idist/build/tordnsel/tordnsel-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/tordnsel/tordnsel-tmp -hidir dist/build/tordnsel/tordnsel-tmp -stubdir dist/build/tordnsel/tordnsel-tmp -package-id HUnit-1.2.2.1-6237339c6ad5673d3cd8f82c4c7f6343 -package-id array-0.3.0.1-438000c197b51c147f229b54edbf632e -package-id base-3.0.3.2-260693a92016991a03206b5a55f6a411 -package-id binary-0.5.1.0-b72d4a82a5aecd9243ff0f50456b3d47 -package-id bytestring-0.9.1.7-64b858f95ff0dacc8acf396bb53cf4b9 -package-id containers-0.3.0.0-ee442470d8dcc9e45f31677c400c5379 -package-id directory-1.0.1.1-fa3418f21f42269537be694d5922dd6d -package-id mtl-1.1.0.2-336254fecf8a77054f76cb33671a5177 -package-id network-2.2.1.7-2eb3746f71ba30c3e4940b75df5ea8b8 -package-id stm-2.1.2.1-95639ea16e2e2cbf4accbabda98a1809 -package-id time-1.1.4-d9f7b7932dc3a4863006ed6b1d525856 -package-id unix-2.4.0.2-94ca14c8a73570f9d75aca642b4de0c6 -O -O2 -Wall -DVERSION="0.1.1-dev" src/tordnsel.hs -lcrypto [ 4 of 39] Compiling TorDNSEL.Util ( dist/build/tordnsel/tordnsel-tmp/TorDNSEL/Util.hs, dist/build/tordnsel/tordnsel-tmp/TorDNSEL/Util.o ) src/TorDNSEL/Util.hsc:143:23: Module `GHC.Handle' does not export `fillReadBuffer' src/TorDNSEL/Util.hsc:143:39: Module `GHC.Handle' does not export `readCharFromBuffer' src/TorDNSEL/Util.hsc:145:26: Module `GHC.IOBase' does not export `Buffer(..)' The flags to ghc indicate that base-3.0.3.2 is being requested, and the documentation for base-3.0.3.2 indicates that GHC.Handle.fillReadBuffer exists[2]. Can anyone explain why I am getting this error message? Could it be because Util is a .hsc rather than .hs file? In tordnsel.cabal I've made two changes: set Build-Depends to include "base>=2.0 && < 4" to tell ghc that I really want base-3 and removed -Werror from GHC-Options (to ignore the deprecation warnings). Otherwise it is as provided in this distribution[3]. Building manually has the same result (though oddly I get a deprecation warning from building the .hs files but not the .hsc file, which led to my suspicion about hsc being an issue. $ hsc2hs TorDNSEL/Util.hsc $ ghc -package-id base-3.0.3.2-260693a92016991a03206b5a55f6a411 --make TorDNSEL/Util.hs [1 of 3] Compiling TorDNSEL.DeepSeq ( TorDNSEL/DeepSeq.hs, TorDNSEL/DeepSeq.o ) TorDNSEL/DeepSeq.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. TorDNSEL/Util.hs:1:11: Warning: -#include and INCLUDE pragmas are deprecated: They no longer have any effect [2 of 3] Compiling TorDNSEL.Compat.Exception ( TorDNSEL/Compat/Exception.hs, TorDNSEL/Compat/Exception.o ) TorDNSEL/Compat/Exception.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. [3 of 3] Compiling TorDNSEL.Util ( TorDNSEL/Util.hs, TorDNSEL/Util.o ) TorDNSEL/Util.hsc:143:23: Module `GHC.Handle' does not export `fillReadBuffer' TorDNSEL/Util.hsc:143:39: Module `GHC.Handle' does not export `readCharFromBuffer' TorDNSEL/Util.hsc:145:26: Module `GHC.IOBase' does not export `Buffer(..)' Thanks in advance, Steven. [1] https://gitweb.torproject.org/tordnsel.git [2] http://hackage.haskell.org/packages/archive/base/3.0.3.2/doc/html/GHC-Handl… [3] https://gitweb.torproject.org/tordnsel.git/blob/HEAD:/tordnsel.cabal

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Subject: A universal data store interface
by Greg Weber 14 Feb '12

14 Feb '12

Hi Sergiu, Thanks you for your interest in that proposal. I rushed it off a year ago. Since then we have made a lot of improvements to Persistent and the library forms a basic building block for most Yesod users and other Haskellers. Persistent offers a level of type-safety and convenience not available elsewhere (except perhaps for libraries like acid-state that are limited to in-memory storage). That being said, there are still a lot of improvements that could be made. With the effort of a GSoC volunteer we could probably get it to the point of being the go-to data storage library for Haskellers, at least those planning on using the subset of backends (likely SQL) with great support. This proposal is vague and we would need to work with you to narrow things down a bit. I am biased, but I believe the Yesod project is one of the most compelling in the Haskell ecosystem. There are a lot of different ways a GSoC project could help make things even better besides improving the associated Persistent library, and we would really like to mentor at least one GSoC student. I would open more tickets for this in the system, but I am not sure how helpful it will be. It seems that we need to reach out to more students like yourself, but I am not sure how to do that unless I see messages like these first. Greg Weber

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