October 2011 - Haskell-Cafe

Trouble defining `instance Arrow SF'
by Captain Freako 28 Oct '11

28 Oct '11

In trying to follow along with `Programming with Arrows' by John Hughes, I'm entering the following code: 1 -- Taken from `Programming with Arrows'. 2 3 module SF where 4 5 import Control.Arrow 6 7 newtype SF a b = SF {runSF :: [a] -> [b]} 8 9 instance Arrow SF where 10 arr f = SF (map f) 11 SF f >>> SF g = SF (f >>> g) and getting the following error from GHCI: GHCi, version 7.0.3: http://www.haskell.org/ghc/ :? for help Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Prelude> :load SF [1 of 1] Compiling SF ( SF.hs, interpreted ) SF.hs:11:10: `>>>' is not a (visible) method of class `Arrow' Failed, modules loaded: none. Can anyone help? Thanks, -db

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Who is working on high performance threadsafe mutable data structures in Haskell?
by Ryan Newton 27 Oct '11

27 Oct '11

Hello cafe, In the context of the monad-par project we're just getting to the point of trying to replace our work stealing Deque's with something more efficient (in Haskell). Based a quick perusal of Hackage there does not seem to be a lot of work in this area. Of course, for Haskell the importance of this topic may be diminished relative to pure data structures, but for doing systems-level work like monad par good concurrent data structures are also very important. We are about to embark on some work to fix this problem for monad-par & Deques, but if there are others working in this vicinity it would be nice to team up. We are going to try both pure Haskell approaches using the new casMutVar# primop as well as wrapping foreign data structures such as those provided by TBB. There are a whole bunch of issues with the latter -- see Appendix A and help me out if you know how to do this. My first goal is to get a parameterizable deque interface, implementation, and benchmarks that makes it possible to express variations of queues including: - Double, single, and 1.5-ended (e.g. both ends can be RW or only R or W) - Threadsafe or single-threaded on both ends - Bounded or unbounded If you require that at least the "left"-end support Write and the "right" end support Read (excluding, for example stacks), that leaves a configuration space of 32 options. Some of these 32 options have much better algorithms than others, but a general algorithm (such as Michael & Scott queues) could satisfy all of them while leaving "room to improve". The TBB guys have considered making their concurrent_queus configurable to this extent but haven't gotten around to it. Thanks, -Ryan Appendix A: Using foreign data structures with Haskell ---------------------------------------------------------------------------- It's easy to call foreign code in Haskell, but how to use a foreign data structure to store polymorphic Haskell values? For example we would want a TBB concurrent_queue to store words representing pointers into the Haskell heap. We would need, for example: - (1) to pin arbitrary objects by making StablePtrs - (2) to communicate those to a foreign enqueue operation - (3) to unpin objects when the pointer is removed from a foreign structure (or use a reference count to determine when to unpin/free the StablePtr) I don't have any experience here and would appreciate hearing from anyone who does. Is this a non-starter? Will the overheads introduced by all the StablePtr ops destroy any gains from using an efficient data structure?

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STM program
by Ketil Malde 27 Oct '11

27 Oct '11

Hi, Café, I'm playing with STM a bit, and did a small writeup. As I'm considering to submit it, uh, tomorrow, I was wondering if anybody would care to take a look? I'm especially nervous about the accuracy and clarity of my descriptions of monads and STM, which are terse and written in a hurry. Anyway: I'd be most grateful for any feedback you care to give. http://malde.org/~ketil/stmcluster.pdf -k -- If I haven't seen further, it is by standing in the footprints of giants

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Really impossible to reinstall `base' using cabal?
by Captain Freako 27 Oct '11

27 Oct '11

In response to this: dbanas@dbanas-eeepc:~$ cabal install arrows Resolving dependencies... Configuring lazysmallcheck-0.6... Preprocessing library lazysmallcheck-0.6... Building lazysmallcheck-0.6... [1 of 1] Compiling Test.LazySmallCheck ( Test/LazySmallCheck.hs, dist/build/Test/LazySmallCheck.o ) Implicit import declaration: Could not find module `Prelude': Perhaps you haven't installed the "dyn" libraries for package `base'? Use -v to see a list of the files searched for. cabal: Error: some packages failed to install: Stream-0.4.6 depends on lazysmallcheck-0.6 which failed to install. arrows-0.4.4.0 depends on lazysmallcheck-0.6 which failed to install. lazysmallcheck-0.6 failed during the building phase. The exception was: ExitFailure 1 I did this: dbanas@dbanas-eeepc:~$ cabal install base and got this: Resolving dependencies... cabal: internal error: impossible Is it really impossible to use cabal to reinstall `base'? Thanks, -db

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Haskell Weekly News: Issue 205
by Daniel Santa Cruz 26 Oct '11

26 Oct '11

Welcome to issue 205 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of October 16 to 22, 2011. You can find an HTML version of this issue at: http://contemplatecode.blogspot.com/2011/10/haskell-weekly-news-issue-205.h… Announcements Ian Lynah sent out a call for nominations for the haskell.org committee. See the link for details on how to submit a nomination. Nominations close on October 29. [1] http://goo.gl/J9J6H New and Updated Projects * netwire (Ertugrul Soeylemez; 1.2.7) [2] http://goo.gl/ULujm Quotes of the Week * kmc: i just used Hayoo to see if anyone implemented this function and it came back with one of my own libraries * JoeyA: LLVM: The easy-to-use compiler infrastructure nobody knows how to use. * kmc: Haskell isn't really designed by mathematicians. it's designed by people who programmers would consider to be mathematicians and mathematicians would consider to be programmers * Cale: foldr is the real fold; foldl is an imposter * @remember hey daniel kmc wants his uploads featured on HWN [edit note: oops, I guess that was meant for me :) +1 for new and inventive ways to communicate!] Top Reddit Stories * Tech-talk about Haskell at Google: Haskell Amuse-Bouche Domain: youtu.be, Score: 86, Comments: 5 On Reddit: [3] http://goo.gl/Pf0NZ Original: [4] http://goo.gl/NPZ17 * Deprecate Prelude.head and partial functions Domain: chrisdone.com, Score: 58, Comments: 60 On Reddit: [5] http://goo.gl/Yat8J Original: [6] http://goo.gl/NyiRO * What does your company use Haskell for? I'll go first. Domain: self.haskell, Score: 51, Comments: 38 On Reddit: [7] http://goo.gl/VOfrO Original: [8] http://goo.gl/VOfrO * I am working on a functional web-programming language as a senior thesis. What do you think so far? Domain: elm-lang.org, Score: 40, Comments: 58 On Reddit: [9] http://goo.gl/6PrQM Original: [10] http://goo.gl/l3odM * Dear Redditor Emac-loving Haskeller(s): what cool emacs Haskell Mode (or custom) features do you use? Domain: self.haskell, Score: 40, Comments: 7 On Reddit: [11] http://goo.gl/LKW0A Original: [12] http://goo.gl/LKW0A * Macros in Haskell Domain: playingwithpointers.com, Score: 38, Comments: 0 On Reddit: [13] http://goo.gl/pwfjt Original: [14] http://goo.gl/bSYN8 * Type-safe event-based programming Domain: jaspervdj.be, Score: 35, Comments: 0 On Reddit: [15] http://goo.gl/gyj9J Original: [16] http://goo.gl/ZBC55 * Yesod excellent ideas Domain: yannesposito.com, Score: 34, Comments: 5 On Reddit: [17] http://goo.gl/ikFJV Original: [18] http://goo.gl/UgBaC * AI Challenge: Ants. Haskell support is only for GHC 6.12. Shall we lobby for 7.0? Domain: aichallenge.org, Score: 28, Comments: 24 On Reddit: [19] http://goo.gl/ShqaM Original: [20] http://goo.gl/O2YOp * Why not Haskell? Domain: neugierig.org, Score: 27, Comments: 26 On Reddit: [21] http://goo.gl/INmRp Original: [22] http://goo.gl/wK3U3 Top StackOverflow Questions * What are some compelling use cases for dependent method types? votes: 44, answers: 2 Read on SO: [23] http://goo.gl/2Xmgu * Why monads? How does it resolve side-effects? votes: 14, answers: 7 Read on SO: [24] http://goo.gl/UJimh * How does Haskell printf work? votes: 13, answers: 1 Read on SO: [25] http://goo.gl/351dE * Why is my genetic algorithm seemingly behaving randomly? votes: 10, answers: 1 Read on SO: [26] http://goo.gl/a5FtH * What are the benefits of applicative parsing over monadic parsing? votes: 10, answers: 4 Read on SO: [27] http://goo.gl/UEkpx * Fixity of backtick operators? votes: 9, answers: 1 Read on SO: [28] http://goo.gl/nwji2 * Bit Size of GHC's Int Type votes: 8, answers: 2 Read on SO: [29] http://goo.gl/DDtFZ * Simple word count in haskell votes: 8, answers: 4 Read on SO: [30] http://goo.gl/ZAYyT * existential search and query without the fuss votes: 8, answers: 2 Read on SO: [31] http://goo.gl/Fnes6 * How to selectively link certain system libraries statically into Haskell program binary? votes: 8, answers: 2 Read on SO: [32] http://goo.gl/HjPTc Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18983 2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/93163 3. http://youtu.be/b9FagOVqxmI 4. http://www.reddit.com/r/haskell/comments/lkiiw/techtalk_about_haskell_at_go… 5. http://chrisdone.com/posts/2011-10-17-boycott-head.html 6. http://www.reddit.com/r/haskell/comments/lf71l/deprecate_preludehead_and_pa… 7. http://www.reddit.com/r/haskell/comments/lfwlv/what_does_your_company_use_h… 8. http://www.reddit.com/r/haskell/comments/lfwlv/what_does_your_company_use_h… 9. http://elm-lang.org/ 10. http://www.reddit.com/r/haskell/comments/liqb4/i_am_working_on_a_functional… 11. http://www.reddit.com/r/haskell/comments/llt44/dear_redditor_emacloving_has… 12. http://www.reddit.com/r/haskell/comments/llt44/dear_redditor_emacloving_has… 13. http://playingwithpointers.com/archives/615 14. http://www.reddit.com/r/haskell/comments/lgeuk/macros_in_haskell/ 15. http://jaspervdj.be/posts/2011-10-16-type-safe-events.html 16. http://www.reddit.com/r/haskell/comments/le2dk/typesafe_eventbased_programm… 17. http://yannesposito.com/Scratch/en/blog/Yesod-excellent-ideas/ 18. http://www.reddit.com/r/haskell/comments/lj2br/yesod_excellent_ideas/ 19. http://aichallenge.org/starter_packages.php 20. http://www.reddit.com/r/haskell/comments/ljs9z/ai_challenge_ants_haskell_su… 21. http://neugierig.org/software/blog/2011/10/why-not-haskell.html 22. http://www.reddit.com/r/haskell/comments/lfv4b/why_not_haskell/ 23. http://stackoverflow.com/questions/7860163/what-are-some-compelling-use-cas… 24. http://stackoverflow.com/questions/7840126/why-monads-how-does-it-resolve-s… 25. http://stackoverflow.com/questions/7828072/how-does-haskell-printf-work 26. http://stackoverflow.com/questions/7792456/why-is-my-genetic-algorithm-seem… 27. http://stackoverflow.com/questions/7861903/what-are-the-benefits-of-applica… 28. http://stackoverflow.com/questions/7807994/fixity-of-backtick-operators 29. http://stackoverflow.com/questions/7786662/bit-size-of-ghcs-int-type 30. http://stackoverflow.com/questions/7803449/simple-word-count-in-haskell 31. http://stackoverflow.com/questions/7813691/existential-search-and-query-wit… 32. http://stackoverflow.com/questions/7832112/how-to-selectively-link-certain-…

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Operator precedence and associativity with Polyparse
by Tom Hawkins 26 Oct '11

26 Oct '11

Hi, Can someone provide guidance on how handle operator precedence and associativity with Polyparse? Thanks in advance. -Tom

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Re: [Haskell-cafe] Open CV or alternate image processing library for Haskell on windows?
by Ivan Perez 26 Oct '11

26 Oct '11

Hi, Sorry for reopening an old thread (May 2011), but I just want to report that I'm using HOpenCV and cv-combinators under windows and I just wanted to tell you that it works just fine. I downloaded the opencv2 libraries as stated on this thread, and I'm successfully building software that works both on Windows (XP and 7, both x86) and Linux (x86 & amd64). The software will be released in a few days, if everything goes well. You'll be able to find it at keera.es, but I'll let you know when I release it anyway. Cheers, Ivan Perez. PS. I just re-subscribed to this mailing list. I can't reply to the old messages (don't have them), and I can't set the old Message-ID with gmail, so I'm providing a link to the original message. [1] http://www.mail-archive.com/haskell-cafe@haskell.org/msg89834.html

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blanket license for Haskell Platform?
by Eric Y. Kow 25 Oct '11

25 Oct '11

So I'm combining Haskell software with some non-free/closed source work. I was wondering what sort of effort it would take to organise a blanket license for everything in the Haskell Platform, and whether it would be worthwhile to anybody. Here's my use case: - I am combining my Haskell [:-)] program with some non-free/closed source [:-(] software - My user is concerned that a large number of having a large number of individual licenses even though textually identical modulo author, date, etc would mean a big hassle getting their lawyers and their user's lawyers to sign off on each and every license I feel a bit embarrassed asking this as it's already great and also very convenient that I can just grab this closed source stuff, but suppose we were to decide that putting together some sort of blanket license for the Haskell Platform would be a good idea. How would we go about organising such an effort? I wonder if this is a sort of thing we could tie to the IHG... Thanks, -- Eric Kow <http://erickow.com>

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Re: [Haskell-cafe] ANNOUNCE: Hac Boston from January *20-22* at MIT
by Edward Kmett 25 Oct '11

25 Oct '11

Correction: January 20-22nd ;) On Tue, Oct 25, 2011 at 5:45 PM, Edward Kmett <ekmett(a)gmail.com> wrote: > I am very pleased to officially announce Hac Boston, a Haskell hackathon > to be held January 21-23, 2012 at MIT in Cambridge, MA. > > The hackathon will officially kick off at 2:30 Friday afternoon, and go > until 5pm on Sunday with the occasional break for sleep. > > Everyone is welcome -- you do not have to be a Haskell guru to attend! > Helping hack on someone else's project could be a great way to increase > your Haskell skills. > > If you plan on coming, please officially register<http://haskell.org/haskellwiki/Hac_Boston/Register>, > even if you already put your name on the wiki. Registration, travel, some > information about lodging and many other details can now be found on the Hac > Boston wiki <http://haskell.org/haskellwiki/Hac_Boston>. > > We have confirmed space for about 30 people, so please register early! > Beyond that we'll have to either seek additional space or close > registration. > > We're also looking for a few people interested in giving short (15-20 min.) > talks, probably on Saturday afternoon. Anything of interest to the > Haskell community is fair game---a project you've been working on, a > paper, a quick tutorial. If you'd like to give a talk, add it on <http://goog_145539007>the > wiki <http://haskell.org/haskellwiki/Hac_Boston/Talks>. > > We look forward to seeing you at MIT! > > -Edward Kmett >

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ANNOUNCE: Hac Boston from January 21-23rd at MIT
by Edward Kmett 25 Oct '11

25 Oct '11

I am very pleased to officially announce Hac Boston, a Haskell hackathon to be held January 21-23, 2012 at MIT in Cambridge, MA. The hackathon will officially kick off at 2:30 Friday afternoon, and go until 5pm on Sunday with the occasional break for sleep. Everyone is welcome -- you do not have to be a Haskell guru to attend! Helping hack on someone else's project could be a great way to increase your Haskell skills. If you plan on coming, please officially register<http://haskell.org/haskellwiki/Hac_Boston/Register>, even if you already put your name on the wiki. Registration, travel, some information about lodging and many other details can now be found on the Hac Boston wiki <http://haskell.org/haskellwiki/Hac_Boston>. We have confirmed space for about 30 people, so please register early! Beyond that we'll have to either seek additional space or close registration. We're also looking for a few people interested in giving short (15-20 min.) talks, probably on Saturday afternoon. Anything of interest to the Haskell community is fair game---a project you've been working on, a paper, a quick tutorial. If you'd like to give a talk, add it on <goog_145539007>the wiki<http://haskell.org/haskellwiki/Hac_Boston/Talks> . We look forward to seeing you at MIT! -Edward Kmett

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