- Haskell-Cafe - Haskell.org

Karatsuba Multiplication Parallel
by Burak Ekici 16 Sep '11

16 Sep '11

Dear All, I am trying to parallelize the below Karatsuba multiplication code. However, at each trial of mine the error message speaking of "incorrect indentation" is returned. I could not come up with ideas to solve the problem. I will be more than glad and appreciated, if any of you sheds light on the issue and point out the problem with its solution. Many thanks in advance, Cheers, Burak. import Control.Parallel import Control.Parallel.Strategies normalize [] = [] normalize (False : xs) = let ns = normalize xs in if ns == [] then [] else (False : ns) normalize (True : xs) = True : (normalize xs) mul [] _ = [] mul (False : xs) ys = False : (mul xs ys) mul (True : xs) ys = mul (False : xs) ys `add` ys mulk3 [] _ = [] mulk3 _ [] = [] mulk3 xs ys = (normalize (mulk3 xs0 ys0)) `add` (replicate l False ++ (((mulk3 (add xs0 xs1) (add ys0 ys1)) `sub` (normalize (mulk3 xs0 ys0)) `sub` (normalize (mulk3 xs1 ys1))) `add` (replicate l False ++ (normalize (mulk3 xs1 ys1))))) where l = (min (length xs) (length ys)) `div` 2 (xs0, xs1) = splitAt l xs (ys0, ys1) = splitAt l ys if l > 32 then (normalize (mulk3 xs0 ys0)) `par` (normalize (mulk3 xs1 ys1)) `par` ((mulk3 (add xs0 xs1) (add ys0 ys1)) `sub` (normalize (mulk3 xs0 ys0)) `sub` (normalize (mulk3 xs1 ys1))) else mul xs ys

2 2

darcs checkin history?? forgot ....
by Vasili I. Galchin 16 Sep '11

16 Sep '11

Hello, If I have a URL for a darcs repository, how can I get a listing of activity ... mainly "checkin" history .... e.g. name, date timestamp? Thanks, Vasili

3 3

Re: [Haskell-cafe] [Haskell] [ANNOUNCE] Haskdogs-0.1
by Ivan Lazar Miljenovic 15 Sep '11

15 Sep '11

Re-cc'ing -cafe: On 14 September 2011 14:29, yi huang <yi.codeplayer(a)gmail.com> wrote: > On Wed, Sep 14, 2011 at 11:32 AM, Ivan Lazar Miljenovic > <ivan.miljenovic(a)gmail.com> wrote: >> >> On 14 September 2011 13:27, yi huang <yi.codeplayer(a)gmail.com> wrote: >> > On Wed, Sep 14, 2011 at 10:18 AM, Ivan Lazar Miljenovic >> > <ivan.miljenovic(a)gmail.com> wrote: >> >> >> >> On 14 September 2011 11:24, yi huang <yi.codeplayer(a)gmail.com> wrote: >> >> > Cabal compains about "Unknown build tool hasktags". >> >> > It seems not necessary to set "Build-tools: hasktags" in cabal file? >> >> >> >> cabal-install isn't capable of automatically building and installing >> >> build-tools for you. So to install haskdogs, you need to do "cabal >> >> install hasktags && cabal install haskdogs". >> > >> > I have installed hasktags, and .cabal/bin is in my PATH, i can run >> > hasktags >> > directly from shell. >> > What else did i miss? >> >> How did you specify your PATH? You can't use ~/.cabal/bin, you need >> either $HOME/.cabal/bin or the fully expanded path. > > It is $HOME/.cabal/bin , and `which hasktags' can find it without problem. > Cabal 1.10.2, ghc 7.0.4, i'm trying to look into cabal source to find the > problem. Actually... looks like you're right. I can't build it either, he appears to have hard-coded some paths in and it appears that you need some kind of magic to register a program as a build tool (that's what the error is from: hasktags isn't a registered build-tool). -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

2 4

Categorized Weaknesses from the State of Haskell 2011 Survey
by Nick Knowlson 15 Sep '11

15 Sep '11

Hello all, I did a followup analysis of the free-form responses to "What is Haskell's most glaring weakness / blind spot / problem" in the State of Haskell 2011 Survey. The article is up at: http://nickknowlson.com/blog/2011/09/12/haskell-survey-categorized-weakness… I think it has a lot of interesting information in it - I hope some others will find it useful now too. Cheers, Nick

8 10

Error in cabal install of monad-par?
by Rishiyur Nikhil 15 Sep '11

15 Sep '11

I'm following the instructions on the CUFP "T5 Parallel Programming in Haskell" web page for preparing for the tutorial, where it asks that I should: 'cabal install monad-par'. I'm doing this on a Mac, Snow Leopard 10.6.8, after installing Haskell Platform. I have Xcode 3.2.4 installed. I get the following error; please let me know how I should fix it (can reply to me personally instead of the list, at 'nikhil at acm dot org'. Thanks. Nikhil $ cabal install monad-par Resolving dependencies... Configuring monad-par-0.1.0.1... Preprocessing library monad-par-0.1.0.1... Building monad-par-0.1.0.1... Control/Monad/Par/Internal.hs:4:15-71: unknown flag in {-# OPTIONS #-} pragma: -fno-warn-unused-do-bind cabal: Error: some packages failed to install: monad-par-0.1.0.1 failed during the building phase. The exception was: ExitFailure 1

1 1

Tupling functions
by Richard O'Keefe 15 Sep '11

15 Sep '11

I would like to have tuple (f1,f2) x = (f1 x, f2 x) tuple (f1,f2,f3) x = (f1 x, f2 x, f3 x) tuple (f1,f2,f3,f4) x = (f1 x, f2 x, f3 x, f4 x) ... I'm aware of Control.Arrow and the &&& combinator, and I can use that instead, but f1 &&& f2 &&& f3 doesn't have _exactly_ the type I want. What should I do?

5 9

efficient chop
by Kazu Yamamoto 15 Sep '11

15 Sep '11

Hello Cafe, I would like to have an efficient implementation of the chop function. As you guess, the chop function drops spaces in the tail of a list. chop " foo bar baz " -> " foo bar baz" A naive implementation is as follows: chopReverse :: String -> String chopReverse = reverse . dropWhile isSpace . reverse But this is not elegant. foldr version is as follows: chopFoldr :: String -> String chopFoldr = foldr f [] where f c [] | isSpace c = [] | otherwise = c:[] f c cs = c:cs But this code is slower than chopReverse in some cases. Are there any more efficient implementations of chop? Any suggestions? --Kazu

9 13

static analysis (call graph) tools?
by Johannes Waldmann 15 Sep '11

15 Sep '11

Dear Cafe, what tools are there for static analysis of Haskell programs? I mean simple things like the call graph (who is calling whom). Which are, of course, not that simple because of higher order functions. Do leksah/eclipsefp(/ghc api) have something like "show all uses of an identifier" (eclipse: "open call hierarchy") (with correct handling of scoping and modules)? Thanks - Johannes.

2 1

Haskell Weekly News: Issue 199
by Daniel Santa Cruz 15 Sep '11

15 Sep '11

Welcome to issue 199 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of September 4 to 10, 2011. Announcements Johannes Waldmann open the invitation to the 6th Haskell in Leipzig workshop, on October 7, 2011. It "will present an absolutely thrilling mixture of tutorials and talks, with special enphasis on parallel programming." [1] http://goo.gl/u0PwF New and Updated Projects * Hs2lib (Phyx; v-0.5.5) A preprocesor and library which allow you to create dynamic libs from arbitrary annotated Haskell programs with one click. It also allows you to use the generated lib in C, C++, and C# just by including the generated header files. [2] http://goo.gl/xCSXc * Netwire (Ertugrul Soeylemez; 1.2.0) Lots of new features! [3] http://goo.gl/VCwb1 * network-address (Sebastian Nowicki; 0.2.0) Provides data structures and textual representation of network addresses (IPv4, IPv6, subnets). [4] http://goo.gl/DBRI6 * Webrexp (Vincent Berthoux; 1.1) A web scraping command line utility. [5] http://goo.gl/OlovQ * eddie (Mike Meyer; 0.5) Is a tool for applying haskell filters to text files via the unix command line. [6] http://goo.gl/NPc0b * cabal-ghci (Etienne Laurin; 0.1) Package to ease the development of projects using cabal. [7] http://goo.gl/fiDKZ Quotes of the Week * gosu: Type parameters are covariant. This is not sound, and that does not matter. * turtlesalltheway: if haskell is so great why cant it improve itself * mm_freak: bosses are generally quite strong, static and lazy * cmccann: newtype Natural = N { denature :: Integer } Top Reddit Stories * Constraint Kinds for GHC Domain: blog.omega-prime.co.uk, Score: 115, Comments: 12 On Reddit: [8] http://goo.gl/bCXgf Original: [9] http://goo.gl/7aWzn * Yesod :: The Limitations of Haskell Domain: yesodweb.com, Score: 108, Comments: 42 On Reddit: [10] http://goo.gl/5q7wW Original: [11] http://goo.gl/gisIh * Frege: haskell like language on JVM (tries to adhere to haskell 2010 where possible) Domain: code.google.com, Score: 58, Comments: 58 On Reddit: [12] http://goo.gl/6KWEg Original: [13] http://goo.gl/56AkX * Sharing in Haskell – How the let and lambda constructs give a precise way to control sharing Domain: neilmitchell.blogspot.com, Score: 34, Comments: 18 On Reddit: [14] http://goo.gl/Uf1vq Original: [15] http://goo.gl/4Hmfu * Let's play a game : How to implement functions from their type signatures Domain: blog.ezyang.com, Score: 24, Comments: 13 On Reddit: [16] http://goo.gl/T2FiD Original: [17] http://goo.gl/SmbYO * Impredicativity + injectivity + type case analysis = inconsistency (Russell paradox) :: Oleg Domain: okmij.org, Score: 23, Comments: 10 On Reddit: [18] http://goo.gl/zoThI Original: [19] http://goo.gl/jFr5U * Functional Pearls Domain: haskell.org, Score: 23, Comments: 1 On Reddit: [20] http://goo.gl/RVyng Original: [21] http://goo.gl/1A7t0 * An EventSource broker written in Haskell Domain: mathias-biilmann.net, Score: 22, Comments: 0 On Reddit: [22] http://goo.gl/7yywu Original: [23] http://goo.gl/Y5mGj * Haskell For Kids: Week 4 Domain: cdsmith.wordpress.com, Score: 22, Comments: 2 On Reddit: [24] http://goo.gl/KwlqD Original: [25] http://goo.gl/xlNh2 * apfelmus - Vault - a persistent store for values of arbitrary types Domain: apfelmus.nfshost.com, Score: 19, Comments: 2 On Reddit: [26] http://goo.gl/VAE4n Original: [27] http://goo.gl/vvQ7A * Tau is available in Haskell, you can safely avoid Pi Domain: hackage.haskell.org, Score: 19, Comments: 26 On Reddit: [28] http://goo.gl/u5GN8 Original: [29] http://goo.gl/VnrMh * Zipper from any Traversable :: Oleg Domain: okmij.org, Score: 18, Comments: 2 On Reddit: [30] http://goo.gl/xi4ZF Original: [31] http://goo.gl/nqZ3T Top StackOverflow Questions * More on generic Scala functions votes: 20, answers: 4 Read on SO: [32] http://goo.gl/DGH14 * Why is a “type class” called “type class”? votes: 20, answers: 2 Read on SO: [33] http://goo.gl/YbVXX * Is there a Haskell idiom for updating a nested data structure? votes: 14, answers: 2 Read on SO: [34] http://goo.gl/jKEjv * How to tell if a list is infinite? votes: 14, answers: 4 Read on SO: [35] http://goo.gl/fc3e6 * Select random element from a set, faster than linear time (Haskell) votes: 9, answers: 5 Read on SO: [36] http://goo.gl/IRJf3 * GHC not optimising modules other than the main module votes: 9, answers: 0 Read on SO: [37] http://goo.gl/8Ephm * A chess board representation in Haskell votes: 8, answers: 4 Read on SO: [38] http://goo.gl/iSM7d * How to cap memory usage of Haskell threads votes: 7, answers: 2 Read on SO: [39] http://goo.gl/dvLnE * Is this Haskell type inference in action, or something else? votes: 7, answers: 2 Read on SO: [40] http://goo.gl/hTaK7 * Assymmetry in the bind function votes: 6, answers: 7 Read on SO: [41] http://goo.gl/KqMTn About the Haskell Weekly News To help create new editions of this newsletter, please send stories to dstcruz(a)gmail.com. Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92287 2. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92182 3. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92225 4. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18916 5. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18929 6. http://permalink.gmane.org/gmane.comp.lang.haskell.general/18930 7. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/92279 8. http://blog.omega-prime.co.uk/?p=127 9. http://www.reddit.com/r/haskell/comments/kbf14/constraint_kinds_for_ghc/ 10. http://www.yesodweb.com/blog/2011/09/limitations-of-haskell 11. http://www.reddit.com/r/haskell/comments/k4lc4/yesod_the_limitations_of_has… 12. http://code.google.com/p/frege/ 13. http://www.reddit.com/r/haskell/comments/kadx6/frege_haskell_like_language_… 14. http://neilmitchell.blogspot.com/2011/09/sharing-in-haskell.html 15. http://www.reddit.com/r/haskell/comments/k4bq9/sharing_in_haskell_how_the_l… 16. http://blog.ezyang.com/2011/09/lets-play-a-game/ 17. http://www.reddit.com/r/haskell/comments/k5okh/lets_play_a_game_how_to_impl… 18. http://okmij.org/ftp/Haskell/impredicativity-bites.html 19. http://www.reddit.com/r/haskell/comments/k5bdb/impredicativity_injectivity_… 20. http://www.haskell.org/haskellwiki/Research_papers/Functional_pearls 21. http://www.reddit.com/r/haskell/comments/kb3w5/functional_pearls/ 22. http://mathias-biilmann.net/posts/2011/9/a-haskell-eventsource-broker 23. http://www.reddit.com/r/haskell/comments/k6fva/an_eventsource_broker_writte… 24. http://cdsmith.wordpress.com/2011/09/10/haskell-for-kids-week-4/ 25. http://www.reddit.com/r/haskell/comments/kbqn0/haskell_for_kids_week_4/ 26. http://apfelmus.nfshost.com/blog/2011/09/04-vault.html 27. http://www.reddit.com/r/haskell/comments/k4l6c/apfelmus_vault_a_persistent_… 28. http://hackage.haskell.org/package/tau 29. http://www.reddit.com/r/haskell/comments/kazfn/tau_is_available_in_haskell_… 30. http://okmij.org/ftp/continuations/zipper.html#traversable 31. http://www.reddit.com/r/haskell/comments/k5bci/zipper_from_any_traversable_… 32. http://stackoverflow.com/questions/7337582/more-on-generic-scala-functions 33. http://stackoverflow.com/questions/7360024/why-is-a-type-class-called-type-… 34. http://stackoverflow.com/questions/7365425/is-there-a-haskell-idiom-for-upd… 35. http://stackoverflow.com/questions/7371730/how-to-tell-if-a-list-is-infinite 36. http://stackoverflow.com/questions/7349080/select-random-element-from-a-set… 37. http://stackoverflow.com/questions/7367070/ghc-not-optimising-modules-other… 38. http://stackoverflow.com/questions/7309554/a-chess-board-representation-in-… 39. http://stackoverflow.com/questions/7297654/how-to-cap-memory-usage-of-haske… 40. http://stackoverflow.com/questions/7342222/is-this-haskell-type-inference-i… 41. http://stackoverflow.com/questions/7319424/assymmetry-in-the-bind-function

1 0

cabal-install to produce a dependency tree
by Ozgur Akgun 14 Sep '11

14 Sep '11

Dear Cafe, What would be the easiest way of generating the following output, given a package name optionally with additional constraints? $- foo "X > 3" "X > 3" depends on A-2.2, B-1.0, C-1.2 A-2.2 depends on D-1.2.3 ... I assume cabal-install internally does this anyway while creating the installation plan, so is there an easy way to get this info out of cabal install? Thanks, Ozgur

1 0