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Propositions in Haskell
by Patrick Browne 17 May '13

17 May '13

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Lambda expressions (core) to categorical form
by Conal Elliott 17 May '13

17 May '13

I want to convert lambda expressions into a vocabulary of monoidal categories, so that they can be given multiple interpretations, including circuit generation and timing analysis, and hopefully some other far-out alternatives (3D visualization, animated evaluation, etc). More specifically, I want a GHC plugin that makes this transformation on GHC's Core language. If you know of related work, have suggestions, and/or are interested in collaborating/consulting, I'd love to hear. Thanks, - Conal

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List comprehensions with Word8
by Jose A. Lopes 17 May '13

17 May '13

Hello everyone, I was playing with Word8 and list comprehensions and the following examples came up. I have to admit the behavior looks quite strange because it does not seem to be consistent. Can someone shed some light on reason behind some of these outputs? By the way, I have abbreviated some outputs with ellipsis ... [1..10] :: [Word8] [1,2,3,4,5,6,7,8,9,10] [1..100] :: [Word8] [1,2,3,4,5,6,7,8,9,10,...,100] [1..1000] :: [Word8] [1,2,3,4,5,6,7,8,9,10,...,232] [1..10000] :: [Word8] [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16] [1..100000] :: [Word8] [1,2,3,4,5,6,7,8,9,10,...,160] [1..1000000] :: [Word8] [1,2,3,4,5,6,7,8,9,10,...,64] [1..10000000] :: [Word8] [1,2,3,4,5,6,7,8,9,10,...,128] [1..100000000] :: [Word8] [] [1..1000000000] :: [Word8] [] Thank you, Jose -- José António Branquinho de Oliveira Lopes Instituto Superior Técnico Technical University of Lisbon

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Re: [Haskell-cafe] Infrastructure for testing the impact of a Functor/Applicative/Monad hierarchy
by Stephen Tetley 16 May '13

16 May '13

Has anyone surveyed the in-print textbooks, tutorials, or tried to assess how much Haskell (H98, H2010, Glasgow Haskell?) is used in teaching? Having the wrong hierarchy is a minor annoyance to us members of the cognoscenti, but a change outside a revision of the language standard could leave a lot of beginners and the teaching material they rely on stranded.

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Parallel ghc --make
by Niklas Hambüchen 16 May '13

16 May '13

I know this has been talked about before and also a bit in the recent GSoC discussion. I would like to know what prevents ghc --make from working in parallel, who worked at that in the past, what their findings were and a general estimation of the difficulty of the problem. Afterwards, I would update http://hackage.haskell.org/trac/ghc/ticket/910 with a short summary of what the current situation is. Thanks to those who know more!

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list comprehension doesn't work
by John 16 May '13

16 May '13

Hi, I have to write a function which returns a list of all pairs (x,y) where x, y ∈ N AND: – x is the product of two natural numbers (x = a · b, where a, b ∈ N) AND – x is really bigger than 5 but really smaller than 500, AND – y is a squer number (y = c² where c ∈ N) NOT greater than 1000, AND – x is a divisor of y. My attempt is as follows: listPairs :: [(Int, Int)] listPairs = [(x,y) | x<-[0..], y<-[0..], x<-[0..]*[0..], x > 5, x < 500, (y*y) < 1001, mod y x == 0] However it doesn't work unfortunatly Could anyone tell me where my mistake is? Thanks. -- View this message in context: http://haskell.1045720.n5.nabble.com/list-comprehension-doesn-t-work-tp5730… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Weekly News: Issue 267
by Daniel Santa Cruz 16 May '13

16 May '13

Welcome to issue 267 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of April 28 to May 11, 2013. Quotes of the Week * ciaranm: a category is just a category in the category of categories * cmccann: the Either monad is like the Maybe monad, except with something instead of Nothing. * sclv: Q: Why are the adjunctions of Galois connections backwards? A: He never got the hang of duals. * acowley: blackdog's experience with IDEs is apparently both more sensual and more culinary than mine * cmccann: shachaf jokes are what the quotes section of HWN is for. cmccann: though lately there have been not as many :[ shachaf: cmccann: Hey, there wasn't a single shachaf quote in the last HWN! shachaf: Leave me alone. shachaf: There were two cmccann quotes. * edwardk: cmccann: i'm NDA'd out of that space for a while ;) elliott: edwardk just collects NDAs so that he can focus. * trapdInIO: in java everything happens elsewhere * edwardk: i never bothered to release the c preprocessor because it was entangled with an old compiler of mind * acowley: I get nervous when I haven't triggered the impossible for more than a month or so :/ * hpc: be careful, excessive consumption of lenses will go straight to your type signature * acowley: The longer I leave this function named "jumanji" the less I want to find a better name * ion: The next step is unsafeCoerce. At that point youâre halfway into implementing lens. * bos: i'm not sure edwardk is a good model to follow. (a) because you won't be able to, and (b) because you won't be able to. Top Reddit Stories * John Carmack interested in doing a moderate-sized project in Haskell Domain: twitter.com, Score: 136, Comments: 30 On Reddit: [1] http://goo.gl/7rJpH Original: [2] http://goo.gl/yL9kV * John Carmack starting port of Wolf 3D in Haskell Domain: twitter.com, Score: 108, Comments: 19 On Reddit: [3] http://goo.gl/MKkiI Original: [4] http://goo.gl/SN7Mp * Haskell for all: Program imperatively using Haskell lenses Domain: haskellforall.com, Score: 103, Comments: 80 On Reddit: [5] http://goo.gl/FIfUd Original: [6] http://goo.gl/zkEHI * unm-hip a Haskell Image Processing Library Domain: self.haskell, Score: 71, Comments: 18 On Reddit: [7] http://goo.gl/erMhx Original: [8] http://goo.gl/erMhx * Crit-bit trees in Haskell: fast, and open to contributors! Domain: github.com, Score: 56, Comments: 16 On Reddit: [9] http://goo.gl/1vQMS Original: [10] http://goo.gl/08byj * Tutorial on HLearn's Markov networks, monoids, and "type level lenses" explained with Futurama Domain: izbicki.me, Score: 53, Comments: 10 On Reddit: [11] http://goo.gl/3mYuD Original: [12] http://goo.gl/4WjnU * Cool mailing list archive I stumbled on: Haskell controlling garbage trucks Domain: haskell.org, Score: 49, Comments: 2 On Reddit: [13] http://goo.gl/h8p4y Original: [14] http://goo.gl/kSGkx * Haskell intuition Domain: self.haskell, Score: 49, Comments: 23 On Reddit: [15] http://goo.gl/F04IM Original: [16] http://goo.gl/F04IM * The Difference between Recursion & Induction Domain: blog.ezyang.com, Score: 47, Comments: 3 On Reddit: [17] http://goo.gl/mZN3T Original: [18] http://goo.gl/z2jZx * Yesod 1.2 released Domain: yesodweb.com, Score: 45, Comments: 8 On Reddit: [19] http://goo.gl/el7dt Original: [20] http://goo.gl/lqBM9 * Haskell 2014 committee has now been formed Domain: thread.gmane.org, Score: 42, Comments: 27 On Reddit: [21] http://goo.gl/okojc Original: [22] http://goo.gl/1g6FG * Web Frameworks Benchmark 4 (includes WAI) Domain: techempower.com, Score: 41, Comments: 60 On Reddit: [23] http://goo.gl/FLGJu Original: [24] http://goo.gl/AJbhV * Haskell for all: pipes-3.3.0: Folds and uniting ListT with Proxy Domain: haskellforall.com, Score: 41, Comments: 14 On Reddit: [25] http://goo.gl/sO1EK Original: [26] http://goo.gl/5rZ0u * First working program using the Repa plugin Domain: disciple-devel.blogspot.com, Score: 39, Comments: 5 On Reddit: [27] http://goo.gl/bQgfV Original: [28] http://goo.gl/9K5Qk * How to use Hoogle from GHCi Domain: youtube.com, Score: 36, Comments: 2 On Reddit: [29] http://goo.gl/9V9o7 Original: [30] http://goo.gl/LU7Zk * 4th Episode of "The Pragmatic Haskeller": HTTP and more Domain: cakesolutions.net, Score: 35, Comments: 3 On Reddit: [31] http://goo.gl/rMLyC Original: [32] http://goo.gl/npjKm * A monadic joke Domain: self.haskell, Score: 34, Comments: 28 On Reddit: [33] http://goo.gl/OmwSp Original: [34] http://goo.gl/OmwSp * A "Natural" Theorem Prover in Haskell — By Tim Gowers! Domain: gowers.wordpress.com, Score: 34, Comments: 5 On Reddit: [35] http://goo.gl/OomyR Original: [36] http://goo.gl/LWNHW * Towards a Haskell Logic Library Domain: spin.atomicobject.com, Score: 30, Comments: 1 On Reddit: [37] http://goo.gl/puVS7 Original: [38] http://goo.gl/7dXA0 * Barabra Liskov - Keynote: The Power of Abstraction Domain: infoq.com, Score: 29, Comments: 25 On Reddit: [39] http://goo.gl/B7AZJ Original: [40] http://goo.gl/SSYSm Top StackOverflow Questions * What constitutes a fold for types other than list? votes: 34, answers: 4 Read on SO: [41] http://goo.gl/AkbgP * Lazy vs Strict implementations of data structures votes: 19, answers: 2 Read on SO: [42] http://goo.gl/De1VO * Compiling very large constants with GHC votes: 17, answers: 1 Read on SO: [43] http://goo.gl/mWOMz * Haskell Tree splitting: Can someone please explain this line? votes: 16, answers: 1 Read on SO: [44] http://goo.gl/ZVaQE * Could cabal notice about unused package in dependencies? votes: 15, answers: 1 Read on SO: [45] http://goo.gl/IUOx2 * How can eta-reduction of a well typed function result in a type error? votes: 14, answers: 2 Read on SO: [46] http://goo.gl/3A4hu * What is so special about Monads? votes: 14, answers: 4 Read on SO: [47] http://goo.gl/CF7BC * Why does ghci desugar type lists and type families? Can this be selectively disabled? votes: 13, answers: 0 Read on SO: [48] http://goo.gl/QBmM7 * How are functors in Haskell and OCaml similar? votes: 13, answers: 1 Read on SO: [49] http://goo.gl/rIYKy * Monitoring GHC activity votes: 10, answers: 1 Read on SO: [50] http://goo.gl/q7WuU * Why isn't the Prelude's words function written more simply? votes: 10, answers: 1 Read on SO: [51] http://goo.gl/W1TqA * How to design a monadic stack? votes: 10, answers: 2 Read on SO: [52] http://goo.gl/LAeJI * How to generate arbitrary instances of a simple type for quickcheck votes: 9, answers: 2 Read on SO: [53] http://goo.gl/oCesk Until next time, +Daniel Santa Cruz References 1. https://twitter.com/ID_AA_Carmack/status/331557216488390656 2. http://www.reddit.com/r/haskell/comments/1dv4ij/john_carmack_interested_in_… 3. https://twitter.com/id_aa_carmack/status/331918309916295168 4. http://www.reddit.com/r/haskell/comments/1dwjup/john_carmack_starting_port_… 5. http://www.haskellforall.com/2013/05/program-imperatively-using-haskell.html 6. http://www.reddit.com/r/haskell/comments/1dpk2b/haskell_for_all_program_imp… 7. http://www.reddit.com/r/haskell/comments/1dzk73/unmhip_a_haskell_image_proc… 8. http://www.reddit.com/r/haskell/comments/1dzk73/unmhip_a_haskell_image_proc… 9. https://github.com/bos/critbit 10. http://www.reddit.com/r/haskell/comments/1e1ywq/critbit_trees_in_haskell_fa… 11. http://izbicki.me/blog/markov-networks-monoids-and-futurama 12. http://www.reddit.com/r/haskell/comments/1e0759/tutorial_on_hlearns_markov_… 13. http://www.haskell.org/pipermail/haskell-cafe/2010-April/075647.html 14. http://www.reddit.com/r/haskell/comments/1df8fy/cool_mailing_list_archive_i… 15. http://www.reddit.com/r/haskell/comments/1e3cl0/haskell_intuition/ 16. http://www.reddit.com/r/haskell/comments/1e3cl0/haskell_intuition/ 17. http://blog.ezyang.com/2013/04/the-difference-between-recursion-induction/ 18. http://www.reddit.com/r/haskell/comments/1dbwp4/the_difference_between_recu… 19. http://www.yesodweb.com/blog/2013/05/yesod-1-2-released 20. http://www.reddit.com/r/haskell/comments/1dko1d/yesod_12_released/ 21. http://thread.gmane.org/gmane.comp.lang.haskell.general/19796 22. http://www.reddit.com/r/haskell/comments/1dhbjr/haskell_2014_committee_has_… 23. http://www.techempower.com/blog/2013/05/02/frameworks-round-4/ 24. http://www.reddit.com/r/haskell/comments/1dk73s/web_frameworks_benchmark_4_… 25. http://www.haskellforall.com/2013/05/pipes-330-folds-and-uniting-listt-with… 26. http://www.reddit.com/r/haskell/comments/1dsuto/haskell_for_all_pipes330_fo… 27. http://disciple-devel.blogspot.com/2013/05/first-working-program-using-repa… 28. http://www.reddit.com/r/haskell/comments/1dm7a6/first_working_program_using… 29. http://www.youtube.com/watch?v=QpDQhGYPqkU 30. http://www.reddit.com/r/haskell/comments/1dxx4m/how_to_use_hoogle_from_ghci/ 31. http://www.cakesolutions.net/teamblogs/2013/04/28/tph-episode-4-http-and-mo… 32. http://www.reddit.com/r/haskell/comments/1d9zou/4th_episode_of_the_pragmati… 33. http://www.reddit.com/r/haskell/comments/1dcfso/a_monadic_joke/ 34. http://www.reddit.com/r/haskell/comments/1dcfso/a_monadic_joke/ 35. http://gowers.wordpress.com/2013/04/14/answers-results-of-polls-and-a-brief… 36. http://www.reddit.com/r/haskell/comments/1dtw7v/a_natural_theorem_prover_in… 37. http://spin.atomicobject.com/2013/05/10/haskell-logic-library/?utm_source=t… 38. http://www.reddit.com/r/haskell/comments/1e2okw/towards_a_haskell_logic_lib… 39. http://www.infoq.com/presentations/programming-abstraction-liskov 40. http://www.reddit.com/r/haskell/comments/1dodfb/barabra_liskov_keynote_the_… 41. http://stackoverflow.com/questions/16426463/what-constitutes-a-fold-for-typ… 42. http://stackoverflow.com/questions/16296571/lazy-vs-strict-implementations-… 43. http://stackoverflow.com/questions/16348340/compiling-very-large-constants-… 44. http://stackoverflow.com/questions/16267497/haskell-tree-splitting-can-some… 45. http://stackoverflow.com/questions/16390273/could-cabal-notice-about-unused… 46. http://stackoverflow.com/questions/16402942/how-can-eta-reduction-of-a-well… 47. http://stackoverflow.com/questions/16439025/what-is-so-special-about-monads 48. http://stackoverflow.com/questions/16346293/why-does-ghci-desugar-type-list… 49. http://stackoverflow.com/questions/16353066/how-are-functors-in-haskell-and… 50. http://stackoverflow.com/questions/16348118/monitoring-ghc-activity 51. http://stackoverflow.com/questions/16446274/why-isnt-the-preludes-words-fun… 52. http://stackoverflow.com/questions/16457111/how-to-design-a-monadic-stack 53. http://stackoverflow.com/questions/16440208/how-to-generate-arbitrary-insta… 54. https://plus.google.com/105107667630152149014/about

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Good to find you on LinkedIn
by Daniel Díaz Casanueva 16 May '13

16 May '13

LinkedIn ------------ Daniel Díaz Casanueva requested to add you as a connection on LinkedIn: ------------------------------------------ Minh Thu, I'd like to add you to my professional network on LinkedIn. - Daniel Accept invitation from Daniel Díaz Casanueva http://www.linkedin.com/e/uc6lxc-hgr1egm6-6q/XvIdBwmueHfd6vFMPXXdLaqreCbl5o… View profile of Daniel Díaz Casanueva http://www.linkedin.com/e/uc6lxc-hgr1egm6-6q/rso/255311896/LIky/name/227245… ------------------------------------------ You are receiving Invitation emails. This email was intended for Minh Thu Vo. Learn why this is included: http://www.linkedin.com/e/uc6lxc-hgr1egm6-6q/plh/http%3A%2F%2Fhelp%2Elinked… (c) 2012, LinkedIn Corporation. 2029 Stierlin Ct, Mountain View, CA 94043, USA.

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Trouble with Debug.Trace when using a library
by hanjoosten 15 May '13

15 May '13

My project is split in two packages, A and B, where B uses A. All together, there are about 100 haskell modules. Currently, there seems to be a loop somewere, that only seems to occur when working with rather large datastructures. I use trace (from Debug.Trace) to see what exactly is going on. As long as I trace functions from B, trace works as expected. However, at some point I need to trace into functions supplied by package A. In package A I have a function like this: (I have simplified the function) fA :: SomeInput -> SomeResult fA a = let x = f a in trace ("Entering fA") x (The function f is defined in package A) In package B, I have a function like this: fB :: SomeInput -> SomeResult fB a = let x = fA a in trace ( "Entering fB") x At runtime, I get the message Entering fB and then nothing more. a lot of cpu is used, but no more output. I have made some wrappers like the ones above. As long as they are in the same package, trace works fine. However, when entering a function from the other package, there is no more debug output. This is very anoying. Anyone some suggestions? Is this a bug? I use the haskell platform 12.4.0.0 on a windows 7 machine. -- View this message in context: http://haskell.1045720.n5.nabble.com/Trouble-with-Debug-Trace-when-using-a-… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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whats with cabal and libgmp.so.3
by Rustom Mody 14 May '13

14 May '13

Today cabal suddenly started giving me errors that libgmp.so.3 is not found Moving away my old .cabal makes it work again Any explanations? [I am on debian testing. I think the causing factor was that debian switched major versions recently. There were a lot of updates... Nothing that looked like it was related to ghc]

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