- Haskell-Cafe - Haskell.org

Google Knol and haskellers
by Yves Parès 13 Oct '11

13 Oct '11

Hi Café, I re-head recently about Google Knol, which is IMO some crossing-over between a wiki and a blog. Are there some people that use it here to write haskell-related articles instead of a regular blog? HAND.

3 2

SSH in community.haskell.org
by Daniel Díaz Casanueva 13 Oct '11

13 Oct '11

Hi Cafe! This is not actually a question about Haskell, but it is related. I sent my request and I have now an account in community.haskell.org. When I was going to use my project, I read these instructions: http://community.haskell.org/admin/using_project.html But I stopped in the first step "If you need to use a shell, SSH to community.haskell.org". OK, I don't have too knowledge in SSH, so I searched the web and found "putty" as an SSH client. I downloaded it and tried it. But, sadly, without success. I put this configuration: Host name: community.haskell.org Port: 22 Connection type: SSH And it connects! Then, server asks me for an user name, and, after I put my user name, it throws the following error: "Disconnected: No supported authentication methods available (server sent: publickey)." Uhmmmm... I have no idea of how to avoid this error. Wrong client? Wrong configuration? Well, I have a public key I didn't put anywhere yet (but in the community registration). I guess I'm lacking some authentication, but I don't know how to solve it. I hope someone can give me some pointers! Thanks in advance! And sorry if this is not a strictly-related Haskell question. Daniel Díaz.

3 4

Haskell Weekly News: Issue 203
by Daniel Santa Cruz 13 Oct '11

13 Oct '11

Welcome to issue 203 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of October 2 to 8, 2011. You can find a HTML version of this issue at: http://contemplatecode.blogspot.com/2011/10/haskell-weekly-news-issue-203.h… Announcements Eric Y. Kow has released the 6th issue of the Parallel Haskell Digest. [1] http://goo.gl/zyIWX Janis Voigtlander issued an invitation to send in contributions for the 21st edition of the Haskell Communities & Activities Report. The more the merrier! [2] http://www.mail-archive.com/haskell-cafe@haskell.org/msg93759.html New and Updated Projects * clientsession (Felipe Almeida Lessa; 0.7.3.1) Fix for security vulnerability. [3] http://goo.gl/Ot8d1 * hit (Vincent Hanquez) An implementation of low level git operations to read and write to a git repository. [4] http://goo.gl/bVxHw * OpenCL (Luis Cabellos; 1.0.1.3) An aparent fork of OpenCLRRaw package, done due to lack of updates from upstream. [5] http://goo.gl/bVxHw * HaTeX (Daniel Diaz Casanueva; 3) A set of combinators which allow you to build LaTeX code, following the LaTeX syntax in a type-safe manner. [6] http://goo.gl/zuW36 * Parsec (Antoine Latter; 3.1.2) A minor point release to the popular monadic combinator library. [7] http://goo.gl/Gx6Y3 * knob (John Millikin) Allows creation of memory-backed handles. [8] http://goo.gl/Jq7kl Quotes of the Week * heatsink: Maybe, (), and Bool go to the Lone Star Bar. The bouncer stops Maybe and says, "we don't serve your kind here." * DanBurton: correction - there will always be a job for programmers to write code to share pictures of cats * quicksilver: what we need is an adapter package any-lens which uses whichever lens package is available then we get potentially the disadvantages of all, without being able to guarantee the advantages of any. * mauke: Go too considered harmful * ddarius: isJust :: Maybe a -> Bool; isJust = unsafeCoerce * ddarius: Well when people say you need a PhD to program Haskell, you can point out that SPJ doesn't have a PhD. Top Reddit Stories * Is Haskell the Cure? Domain: mathias-biilmann.net, Score: 60, Comments: 60 On Reddit: [9] http://goo.gl/d84BE Original: [10] http://goo.gl/wMrH3 * Writing Functions With Many Nameless Parameters Domain: blog.atnnn.com, Score: 41, Comments: 6 On Reddit: [11] http://goo.gl/nLyGE Original: [12] http://goo.gl/uQkke * Want to help with the new hackage server? Jump in now... Domain: haskell.org, Score: 37, Comments: 0 On Reddit: [13] http://goo.gl/kV1gk Original: [14] http://goo.gl/i2Hbk * Slides from my talk on benchmarking and other random topics at IFL Domain: slideshare.net, Score: 32, Comments: 14 On Reddit: [15] http://goo.gl/SKJuH Original: [16] http://goo.gl/zRTwy * "OCaml For the Masses" article on Slashdot Domain: developers.slashdot.org, Score: 30, Comments: 49 On Reddit: [17] http://goo.gl/isVQ3 Original: [18] http://goo.gl/wlKaa * WebSockets support for WAI/Warp/Yesod: Thanks to Jasper's awesome work Domain: github.com, Score: 27, Comments: 6 On Reddit: [19] http://goo.gl/bpjUC Original: [20] http://goo.gl/bpjUC * A good explanation of the fixed point combinator in Haskell Domain: playingwithpointers.com, Score: 25, Comments: 9 On Reddit: [21] http://goo.gl/C8JmY Original: [22] http://goo.gl/zZnDO * ANNOUNCE: knob, a library for memory-backed handles Domain: haskell.org, Score: 24, Comments: 9 On Reddit: [23] http://goo.gl/JicDL Original: [24] http://goo.gl/xO2tY * HaTeX 3 is out! Domain: deltadiaz.blogspot.com, Score: 23, Comments: 17 On Reddit: [25] http://goo.gl/PVB9h Original: [26] http://goo.gl/aK8Tl * What should I use for web programming? Domain: self.haskell, Score: 22, Comments: 30 On Reddit: [27] http://goo.gl/74r1H Original: [28] http://goo.gl/74r1H * Practice for helping Java & C++ programmers learn Haskell: read programs with them, out loud Domain: cliffordbeshers.blogspot.com, Score: 21, Comments: 4 On Reddit: [29] http://goo.gl/6Cf2o Original: [30] http://goo.gl/P1pD1 * Creative partner request from a Haskell course's message board Domain: imgur.com, Score: 19, Comments: 5 On Reddit: [31] http://goo.gl/ZVWjs Original: [32] http://goo.gl/zW5Yf Top StackOverflow Questions * Clean and type-safe state machine implementation in a statically typed language? votes: 17, answers: 11 Read on SO: [33] http://goo.gl/GRI9p * What happens if an Enumerator tries to consume input? votes: 16, answers: 1 Read on SO: [34] http://goo.gl/bnTJD * Are there type signatures which Haskell can't verify? votes: 11, answers: 2 Read on SO: [35] http://goo.gl/0rfQe * Comparision of enumerator vs. iteratee package votes: 11, answers: 1 Read on SO: [36] http://goo.gl/iR9E1 * Will a value that has a type with class constraints actually be a function at run time? votes: 10, answers: 4 Read on SO: [37] http://goo.gl/o4zDC * Overloading (+) votes: 9, answers: 2 Read on SO: [38] http://goo.gl/Muxre * Strange type error in Haskell let-expression — what's the issue? votes: 9, answers: 3 Read on SO: [39] http://goo.gl/gKLSX * Haskell type declarations in 'where' — what's going on? votes: 8, answers: 2 Read on SO: [40] http://goo.gl/YIydy * Why is `http` in http-enumerator an Iteratee? votes: 8, answers: 1 Read on SO: [41] http://goo.gl/y3qQA * How to check for haskell package versions in ./configure? votes: 8, answers: 5 Read on SO: [42] http://goo.gl/o4EIu * Polynomial factorization in Haskell votes: 8, answers: 2 Read on SO: [43] http://goo.gl/nca2Z Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92911 2. http://www.mail-archive.com/haskell-cafe@haskell.org/msg93759.html 3. http://permalink.gmane.org/gmane.comp.lang.haskell.yesod/503 4. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92871 5. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92836 6. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92908 7. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18972 8. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18974 9. http://mathias-biilmann.net/posts/2011/10/is-haskell-the-cure 10. http://www.reddit.com/r/haskell/comments/kza1y/is_haskell_the_cure/ 11. http://blog.atnnn.com/p/writing-haskell-functions-with-many-nameless-parame… 12. http://www.reddit.com/r/haskell/comments/kz8gx/writing_functions_with_many_… 13. http://www.haskell.org/pipermail/cabal-devel/2011-October/007803.html 14. http://www.reddit.com/r/haskell/comments/l3zye/want_to_help_with_the_new_ha… 15. http://www.slideshare.net/bos31337/pronk-like-you-mean-it 16. http://www.reddit.com/r/haskell/comments/l04nj/slides_from_my_talk_on_bench… 17. http://developers.slashdot.org/story/11/10/04/1557206/ocaml-for-the-masses 18. http://www.reddit.com/r/haskell/comments/l1jyt/ocaml_for_the_masses_article… 19. https://github.com/yesodweb/wai/blob/master/wai-websockets/Network/Wai/Hand… 20. http://www.reddit.com/r/haskell/comments/l2421/websockets_support_for_waiwa… 21. http://playingwithpointers.com/archives/590 22. http://www.reddit.com/r/haskell/comments/l4gmb/a_good_explanation_of_the_fi… 23. http://www.haskell.org/pipermail/haskell-cafe/2011-October/095896.html 24. http://www.reddit.com/r/haskell/comments/l5mwt/announce_knob_a_library_for_… 25. http://deltadiaz.blogspot.com/2011/10/hatex-3-first-release.html 26. http://www.reddit.com/r/haskell/comments/l38md/hatex_3_is_out/ 27. http://www.reddit.com/r/haskell/comments/l0fne/what_should_i_use_for_web_pr… 28. http://www.reddit.com/r/haskell/comments/l0fne/what_should_i_use_for_web_pr… 29. http://cliffordbeshers.blogspot.com/2011/10/conalelliott-re-what-resources.… 30. http://www.reddit.com/r/haskell/comments/l0k0w/practice_for_helping_java_c_… 31. http://imgur.com/mTxC4 32. http://www.reddit.com/r/haskell/comments/l3ah1/creative_partner_request_fro… 33. http://stackoverflow.com/questions/7699912/clean-and-type-safe-state-machin… 34. http://stackoverflow.com/questions/7683408/what-happens-if-an-enumerator-tr… 35. http://stackoverflow.com/questions/7644658/are-there-type-signatures-which-… 36. http://stackoverflow.com/questions/7674594/comparision-of-enumerator-vs-ite… 37. http://stackoverflow.com/questions/7659845/will-a-value-that-has-a-type-wit… 38. http://stackoverflow.com/questions/7646624/overloading 39. http://stackoverflow.com/questions/7662937/strange-type-error-in-haskell-le… 40. http://stackoverflow.com/questions/7635720/haskell-type-declarations-in-whe… 41. http://stackoverflow.com/questions/7638326/why-is-http-in-http-enumerator-a… 42. http://stackoverflow.com/questions/7645823/how-to-check-for-haskell-package… 43. http://stackoverflow.com/questions/7687792/polynomial-factorization-in-hask…

1 0

cabal license check?
by Eric Y. Kow 12 Oct '11

12 Oct '11

Hi all, I'd like a tool that takes a .cabal file as input and produces a list of all dependencies (recursive, all the way to 'base') and some metadata for each (most importantly, LICENSE) Does this already exist, or will I to write it myself? I notice that there's a patch by Trevor Elliot to either Cabal or cabal-install that does something similar [1], and I know that Magnus Therning wrote a little tool that creates a GraphViz graph [2]... so it seems like all the pieces are there already. But is there anything in some sort of ready-to-go just-works state, doing everything including interacting with hackage and sucking down the cabal files it needs, etc? Thanks, Eric [1]: http://www.haskell.org/pipermail/cabal-devel/2010-October/006657.html [2]: http://therning.org/magnus/archives/534 -- Eric Kow <http://erickow.com>

3 3

Up and Down the Latter of Abstraction
by Lyndon Maydwell 12 Oct '11

12 Oct '11

Hi Cafe. I came across an interesting page about interactive abstraction called "Up and Down the Latter of Abstraction" [1] while browsing hacker-news. Under the appendix "Tools & Implementation" Bret Victor ponders: "Perhaps language theorists will stop messing around with arrows and dependent types, and start inventing languages suitable for interactive development and discovery." I don't subscribe to the idea that static guarantees and functional characteristics are mutually exclusive to interactive development and discovery and I think they may actually complement each other extremely well, but this page certainly does sell the interactive aspect very effectively. The closest I've seen to this proces from Haskell seems to have come from "luite" and co (correct me if I'm wrong) and their work on the Diagrams package and its surrounding infrastructure [2], however, their interactive demonstrations no longer seem to be online. Still, the dominant interface seems to be web-based, and I feel that a native environment for this kind of explorative interactive programming would be more effective. Other languages that seem to be especially effective at this kind of development are Processing [3] and Mathematica [4]. Has anyone had experience with interactive development in Haskell? [1] - http://worrydream.com/LadderOfAbstraction/ -- "Appendix: Tools & Implementation" [2] - http://pnyf.inf.elte.hu/fp/Diagrams_en.xml [3] - http://processing.org/ [4] - http://www.wolfram.com/mathematica/

4 4

Fwd: [Haskell] ANN: global-variables-1.0
by Jean-Marie Gaillourdet 12 Oct '11

12 Oct '11

Begin forwarded message: > From: Jean-Marie Gaillourdet <jmg(a)gaillourdet.net> > Subject: Re: [Haskell] ANN: global-variables-1.0 > Date: 12. Oktober 2011 20:27:16 MESZ > To: Henning Thielemann <lemming(a)henning-thielemann.de> > > Hi, > > On 12.10.2011, at 20:20, Henning Thielemann wrote: > >> >> On Wed, 12 Oct 2011, Jean-Marie Gaillourdet wrote: >> >>> * Simplify the "configuration problem" - at least for code in the >>> IO monad. >>> >>> Note, that this library does not encourage sloppy software design by >>> re-introducing all bad effects of global variables. >> >> But isn't this kind of solution for the "configuration problem" an example for sloppy software design? If a global configuration would be passed around, then you could easily use the program functions with different configurations simultaneously. In contrast to that, with the global IORef this is not possible. > > Well, the question whether using a carefully documented set of global configuration variables which, e.g. only affect the verbosity of logging, is sloppy or not is a question I don't want to answer. But I am convinced there are good reasons to use global-variables *sometimes*. If only for a temporary debugging aid. In any case, an additional possibility to express design intents never hurts. > > Note, that I wrote "simplify" not solve "the configuration problem" :-) > > Cheers, > Jean

1 0

ANN: global-variables-1.0
by Jean-Marie Gaillourdet 12 Oct '11

12 Oct '11

Hi, I am pleased to announce the first public release of global-variables. A package providing a global namespace for IORefs, MVars, and TVars. Hackage URL: http://hackage.haskell.org/package/global-variables-1.0 Source: http://bitbucket.org/jmg/global-variables/ Description: ---------------- 'Data.Global' provides a global namespace of 'IORef's, 'MVar's and 'TVar's. This namespace may be accessed in pure code. Yet reading and writing to those 'IORef's, 'MVar's and 'TVar's happens still in their respective monads. 'Data.Global' is designed to meet the following use cases: * Simplify the declaration of top-level mutable variables, by avoiding any pragmas as well as 'unsafePerformIO'. * Avoid having to pass references explicitly throughout the program in order to let distant parts communicate. * Enable a communication by convention scheme, where e.g. different libraries may communicate without code dependencies. * Simplify the "configuration problem" - at least for code in the IO monad. Note, that this library does not encourage sloppy software design by re-introducing all bad effects of global variables. Nevertheless, sometimes global variables are a suitable solution to a problem. In that case "Data.Global" simplifies and extends their handling significantly. Example: ------------- > module Main where > > import Data.Global > import Data.IORef > > counter :: IORef Int > counter = declareIORef "Main.counter" 0 > > main :: IO () > main = do > counter `writeIORef` 1 > readIORef counter >>= print Note absence of pragmas and of unsafePerformIO! Future Plans: ------------------ * Support discovery/traversal of existing variables * TemplateHaskell support to generate private and unique variable names. Regards, Jean

2 1

Re: [Haskell-cafe] SMP parallelism increasing GC time dramatically
by Tom Thorne 12 Oct '11

12 Oct '11

The speedup is around 6 times on a 12 core machine, which I think is pretty decent given that the parallelised section is only a part of my code. The nested parMaps were left over from a previous implementation, I have moved to using just the inner one, since the outer map doesn't divide the work equally and causes one thread to do most of the work. On Mon, Oct 10, 2011 at 4:04 PM, Christopher Brown <cmb21(a)st-andrews.ac.uk>wrote: > What kinds of speedup are you getting? > > 422000 is a lot of sparks, could be due to the fact you are nesting your > par maps (why do you do this?) > > Chris. > > > > On 10 Oct 2011, at 15:44, Tom Thorne wrote: > > thanks! I just tried setting -A32M and this seems to fix the parallel GC > problems, I now get a speedup with parallel GC on and performance is the > same as passing -qg. I had tried -H before and it only made things worse, > but -A seems to do the trick. > > I'm still having problems with segmentation faults though. Depending on how > I apply parMap, and whether I use monad-par or control.parallel, they seem > to come and go arbitrarily. In a successful run that lasted about 30s in > total with control.parallel, +RTS -s reports: > SPARKS: 422712 (394377 converted, 0 pruned) > > am I creating too many sparks? > > On Mon, Oct 10, 2011 at 3:07 PM, Gregory Collins <greg(a)gregorycollins.net>wrote: > >> On Mon, Oct 10, 2011 at 3:55 PM, Tom Thorne <thomas.thorne21(a)gmail.com> >> wrote: >> > >> > Yes I will try to run threadscope on it, I tried it before and the event >> log output produced about 1.8GB, and then crashed. >> > Is there any way to tell the RTS to perform GC less often? My code >> doesn't use too much memory and I'm using fairly hefty machines (e.g one >> with 48 cores and 128GB of RAM) and so perhaps the default/heuristic >> settings aren't optimal. >> >> Increasing "-A" and "-H" in the RTS options should help with this. >> >> G >> -- >> Gregory Collins <greg(a)gregorycollins.net> >> > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > >

1 0

Arrow based re-definition of `StateT' included in `Control.Arrow.'?
by Captain Freako 12 Oct '11

12 Oct '11

Hi all, Is the Arrow-based re-definition of `StateT' included somewhere in the `Control.Arrow.' stack, or do you put the code into your program explicitly? Thanks, -db

3 2

Combining stream and list fusion
by Bas van Dijk 12 Oct '11

12 Oct '11

Hello, I'm trying to make the following faster: Data.Vector.Generic.fromList list where 'list' is some expression yielding a list. (For example: map (+1) $ map (*2) [1..1000000]) Note that Data.Vector.Generic.fromList is defined as: fromList :: Vector v a => [a] -> v a {-# INLINE fromList #-} fromList = unstream . Stream.fromList where Stream.fromList is defined in Data.Vector.Fusion.Stream as: fromList :: [a] -> Stream a {-# INLINE fromList #-} fromList = M.fromList where M.fromList is defined in Data.Vector.Fusion.Stream.Monadic as: fromList :: Monad m => [a] -> Stream m a {-# INLINE fromList #-} fromList xs = unsafeFromList Unknown xs where unsafeFromList is defined as: unsafeFromList :: Monad m => Size -> [a] -> Stream m a {-# INLINE_STREAM unsafeFromList #-} unsafeFromList sz xs = Stream step xs sz where step (x:xs) = return (Yield x xs) step [] = return Done I would like to fuse the construction of the list with the construction of the stream as in: import GHC.Base ( build ) {-# RULES "unsafeFromList/build" forall sz (g :: forall b. (a -> b -> b) -> b -> b). unsafeFromList sz (build g) = unsafeFromListF sz g #-} unsafeFromListF :: forall m a. Monad m => Size -> (forall b. (a -> b -> b) -> b -> b) -> Stream m a {-# INLINE unsafeFromListF #-} unsafeFromListF sz g = Stream step st sz where St step st = g c z c :: a -> St m a -> St m a c x st = St (\(St s st') -> s st') (St (\s -> return (Yield x s)) st) z :: St m a z = St (\_ -> return Done) undefined -- Ouch! data St m a = St ((St m a) -> m (Step (St m a) a)) (St m a) Unfortunately, some initial experiments show that this doesn't make it faster. Are there ways to improve this? (Bonus points for getting rid of the undefined!) Regards, Bas

2 1