- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] octree implementation - followup to "How to model outer space for a MUD"
by Michal J Gajda 23 Aug '15

23 Aug '15

Hi, And if you search for Octree on Hackage, you would have also found my Octree implementation. It does not do re-balancing, but in this type of application you talk about it may not be needed. http://hackage.haskell.org/package/Octree Funny part, is that implementation may be easier to read than algo description I read first time: http://hackage.haskell.org/package/Octree-0.5.4.2/docs/src/Data-Octree-Inte… . It worked perfectly for my use cases (checking for collisions of 1000-100000 objects), but (just in case) the initial creation from list structure make the octree balanced. Note that balanced octree is supposed to be much faster than KD-tree, and may be also faster than R-tree in memory, since it is very shallow structure - log_8 between 10k and 1m changes only from below 5 to below 7! I was also very happy with its cache behaviour, although in theory R-tree could be better. I am also extremely interested in making sure that Haskell has a good choice of multidimensional metric data structures, so I am closely following maintenance of kd-tree, Ashley´s, and Gloss´ quadtrees. And if you really want to have re-balancing, please contact me on my email. -- Best regards Michal

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HAL-10 (preliminary announcement)
by Johannes Waldmann 22 Aug '15

22 Aug '15

Dear all, > ... this year's Haskell in Leipzig I have been busy with many other things, so there are no concrete plans right now. But I think we should do it, and I am willing to host it at my institution. So - how about December 4/5 (Friday noon - Saturday noon)? (it is easier to get lecture rooms on the week-end) If you have comments or suggestions for HAL this year, then please email me, or stammtisch at haskell.iba-cg.de , or someone could set up a wiki page somewhere. Let's say we start collecting opinions now, and make a decision and a formal announcement end of September. http://www.imn.htwk-leipzig.de/~waldmann/HAL2015/ - Johannes Waldmann.

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Haskell Weekly News
by Kim-Ee Yeoh 21 Aug '15

21 Aug '15

*Top picks:* - Gabriel Gonzalez evaluates Haskell <https://github.com/Gabriel439/post-rfc/blob/master/sotu.md> in the style of a State-of-the-Union address. He rates Haskell from Immature to Mature to Best-in-class under 28 headings, the first four being *Compilers,* *Server-side web programming,* *Scripting / Command-line applications,* and *Numerical programming.* He also recommends libraries and tutorials under each heading. Reverberations on Hacker News <https://news.ycombinator.com/item?id=10071535> and /r/haskell <https://www.reddit.com/r/haskell/comments/3haulk/state_of_the_haskell_ecosy…> . - Challenged over claims of FP productivity improvement, Douglas M. Auclair rattles off success stories from his previous work <http://logicaltypes.blogspot.com/2015/08/pure-functional-programming-claims…> at various subsidiaries of the US Federal Gov fending for the taxpayer to the tune of billions of dollars. Nibbles of interest on Hacker News <https://news.ycombinator.com/item?id=10057661>. - Aaron Wolf goes from zero programming directly to Haskell and writes of his experience. <https://snowdrift.coop/p/snowdrift/blog/technical-history> His favorite learning resource is the Haskell Wikibook <https://en.wikibooks.org/wiki/Haskell>, which he can improve as he reads. He is co-founder of Snowdrift.coop, a crowdfunding platform for freely-licensed works <https://snowdrift.coop/p/snowdrift/w/en/about>. The Haskell Reddit <https://www.reddit.com/r/haskell/comments/3hbrom/learning_haskell_from_noth…> finds Aaron's testimony a change from the "Haskell is too hard for me" meme. - The season of introspection continues. On the heels of Hu, Hughes, and Wang on "How Functional Programming Mattered" (see previous HWN <http://haskell.1045720.n5.nabble.com/Fwd-Haskell-Weekly-News-tp5815292.html>); Michael Green, Kathleen Fisher, and David Walker <http://tmpl.weaselhat.com/> track the ebb and flow of research topics in the conference proceedings of the Big Four: Principles of PL (POPL), PL Design and Implementation (PLDI), International Conference on FP (ICFP); and OOP, Systems, Languages, Apps (OOPSLA). No mention of Haskell but if you're looking for a brief history of PL research -- the slides are even more succinct <http://www.cs.ox.ac.uk/ralf.hinze/WG2.8/33/slides/Kathleen.pdf> -- this is the only data-driven survey you'll find. - Doug Beardsley <http://softwaresimply.blogspot.com/2015/08/why-version-bounds-cannot-be-inf…> reminds us that date-based version inference cannot replace the role of explicit version upper bounds. The reason? The package developer might not be using the latest version of its dependencies on the day they publish the work. Also, among the 72 comments of the /r/haskell convo <https://www.reddit.com/r/haskell/comments/3h83jl/why_version_bounds_cannot_…>, Doug observes that Stackage over-conservatively locks to a single version, whereas community-wide adherence to the Package Versioning Policy (PVP) of original hackage <https://wiki.haskell.org/Package_versioning_policy> yields seamless delivery of bugfixes and improvements. - In less than a week, Xmonad will lose its issue tracking system. On Aug 24, Google Code goes read-only <http://google-opensource.blogspot.sg/2015/03/farewell-to-google-code.html>. Community heroes Brandon Allbery and Daniel Wagner <http://haskell.1045720.n5.nabble.com/google-code-issues-td5815183.html> work at grabbing a backup of the issues. Still no consensus over what and where to migrate to. - Mark Dominus <http://blog.plover.com/aliens/dd/> delves into the bits and bytes of the 1999 Cosmic Call <http://en.wikipedia.org/wiki/Cosmic_Call> attempt by astrophysicists to contact aliens. He shows the visual bitmaps transmitted into space. Brent Yorgey <http://mathlesstraveled.com/2015/08/19/cosmic-call-at-the-universe-of-disco…> writes to say he enjoys the 23-part series interspersed with little puzzles. *Quotes of the Week:* - Doug McIlroy <http://ircbrowse.net/browse/haskell?id=20962286&timestamp=1435683815#t14356…>: Conditional compilation is admitting defeat. - /u/kamatsu <https://www.reddit.com/r/haskell/comments/3h5og6/i_now_tend_to_think_that_t…>: I feel like the reason people find Haskell an eye-opening experience is because their CS education was deficient. - @wfaler <https://twitter.com/wfaler/status/631815511949615104>: Is there a club to join when you silently sob at having to give your Monad Transformers Monad Transformers? Sounds a lot like #EnterpriseFP -- Kim-Ee

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Re: [Haskell-cafe] List of nitpicks
by Johannes Waldmann 21 Aug '15

21 Aug '15

> Should there be a similar place for tooling and libraries? a Gargantuan task > QuickCheck fails by letting all tests pass > when you mistakenly provide polymorphic type signatures. No! Prelude Test.QuickCheck> quickCheck $ ( (\ x -> 1 > 9) :: a -> Bool) *** Failed! Falsifiable (after 1 test): () I think you mean "defaults everything to () and thus runs polymorphic tests at unexpected types" Prelude Test.QuickCheck> quickCheck $ ( (\ xs -> xs == reverse xs ) :: Eq a => [a] -> Bool) +++ OK, passed 100 tests. - J.W.

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Reactive config file generation
by David Turner 20 Aug '15

20 Aug '15

Hi all, I am using Apache Zookeeper as a service directory: I have a bunch of services which announce their presence by making nodes in Zookeeper, so that dependent services can update their configuration to make use of the available services, and stop trying to use services that have died. Zookeeper is a pretty nice fit for this because it supports watching a node for changes, so in theory there is no need to poll Zookeeper periodically. The services that I control work with this just fine, but there are some (e.g. an Nginx reverse-proxy) that are reconfigured using the rather more common approach of updating a file (or files) and then sending the process a signal. I am currently pondering how to make this work without polling, or manually triggering a refresh script, which is how it is currently done. I've never used FRP, but am at least vaguely aware of it and from my high-level understanding it seems like this could be a very good fit. The Zookeeper state is a time-varying value which I want to convert into a time-varying set of files, ideally as declaratively as possible. So, two questions to the FRP congnoscenti out there. Firstly, is it worthwhile to attempt this using FRP at all? I'm sure I could do it by hand too. Secondly, which of the many FRP libraries would you recommend for it? There are loads on the Wiki, seemingly in various states of repair and documentation. Any pointers on how to choose one that's featureful enough, performant enough, and being actively maintained? Thanks in advance, David

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ANN: cabal-bounds 1.0.0
by Daniel Trstenjak 20 Aug '15

20 Aug '15

cabal-bounds[1] is a command line programm for managing the bounds/versions of the dependencies in a cabal file. Changes for 1.0.0 ================= * automatically find the cabal and setup-config files * ignore the base library by default Perhaps the two most relevant use cases: Initialize Bounds ================= If you have started a new project, created a cabal file, added dependencies to it, build it, and now want to set the lower and upper bounds of the dependencies according to the currently used versions of the build, then you can just call: $> cabal-bounds update This call will update the bounds of the dependencies of the cabal file in the working directory. Raise the Upper Bounds ====================== If you have several cabalized projects, then it can be quite time consuming to keep the bounds of your dependencies up to date. Especially if you're following the [package versioning policy](<http://www.haskell.org/haskellwiki/Package_versioning_policy>), then you want to raise your upper bounds from time to time, to allow the building with newer versions of the dependencies. `cabal-bounds` tries to automate this update process to some degree. So a typical update process might look like: # update the version infos of all libraries $> cabal update # drops the upper bound of all dependencies of the cabal file in the working directory $> cabal-bounds drop --upper # create a cabal sandbox for building your project, this ensures that you're really using # the newest available versions of the dependencies, otherwise you would be constraint # to the already installed versions $> cabal sandbox init # build your project $> cabal install # update the upper bound of all dependencies of the cabal file in the working directory $> cabal-bounds update --upper Please consult the README for further informations. [1] https://github.com/dan-t/cabal-bounds

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octree implementation - followup to "How to model outer space for a MUD"
by Michael Litchard 20 Aug '15

20 Aug '15

It looks like Octree is what I want if I can solve a particular problem. First let me articulate what I am looking for. (1) Objects in 3-d space with no spatial extent. Collision is determined by two objects occupying the same point.' (2) Efficient insert-delete-update #2 seems to be the problem. I found this library, thankfully. I believe it's exactly what I am looking for, but for quadtrees. https://github.com/AshleyMoni/QuadTree I'm a little overwhelmed as this is a new data structure for me. I believe if I can grok what is going on in this library, I can take these ideas and extend them to the octree. I'm referring specifically to this module https://github.com/AshleyMoni/QuadTree/blob/master/Data/QuadTree/Internal.hs And these functions setLocation :: Eq a => Location -> a -> QuadTree a -> QuadTree a setLocation = set . atLocation atLocation (Having difficulty cutting and pasting this to mail.) I'd like to be able to visualize how the tree is being compressed, it may help to be able to see what happens to the tree when it's not compressed. Does anyone have a pointer or advice in how to break this library down in parts to help me grok, in a way that will help me extend to octree?

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List of nitpicks
by William Yager 20 Aug '15

20 Aug '15

Hello all, Inspired by the recent thread re. modifying data/type/newtype syntax, I've made a wiki article dedicated to Haskell-related nitpicks. I've added a few entries; one from the thread I just mentioned, and a classic from way back in the 90s (map vs fmap). https://wiki.haskell.org/Nitpicks Hopefully, this page will help us keep track of what people are annoyed about (especially people who aren't already inured to the quirks of Haskell) as well as give us inspiration for future proposals. Cheers, Will

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Problem parallelising simple algorithm
by Jens Blanck 20 Aug '15

20 Aug '15

The following code simply computes the Euler constant by binary splitting. I'm struggling to get any speed-up on multi-core. Why do I get a fair number of fizzled? Why don't I get any real speed-up even if it claims to run tasks in parallel? Could I have exhausted the integer arithmetic unit(s) on my chip (i7-4790)? How would I verify that? The following is the code and typical runs on 1 and 4 cores respectively. --------- import Control.Parallel.Strategies import Control.DeepSeq import Data.Ratio divConq :: (NFData b) => (a -> b) -> a -> (a -> Bool) -> (b -> b -> b) -> (a -> Maybe (a,a)) -> b divConq f arg threshold conquer divide = go arg where go arg = case divide arg of Nothing -> f arg Just (l0,r0) -> conquer l1 r1 `using` strat where l1 = go l0 r1 = go r0 strat x = do r l1; r r1; return x where r | threshold arg = rdeepseq | otherwise = rpar pqCombine :: (Integer, Integer) -> (Integer, Integer) -> (Integer, Integer) pqCombine (pl, ql) (pr, qr) = (pl*qr+pr, ql*qr) pq :: (Integer, Integer) -> (Integer, Integer) pq (a, b) = (\t -> (sum t, last t)) $ scanl1 (*) [b,b-1..a+1] euler :: Integer -> Rational euler n = let (p,q) = divConq pq (0,n) (\(a,b) -> b-a < 10000) pqCombine (\(a,b) -> if b-a > 5 then let m = (a+b+1) `div` 2 in Just ((a,m), (m, b)) else Nothing) in p%q main = print $ euler 320000 `seq` () ---------- > ./BinSplit +RTS -s -N1 () 178,375,880 bytes allocated in the heap 2,452,040 bytes copied during GC 3,222,696 bytes maximum residency (7 sample(s)) 883,040 bytes maximum slop 11 MB total memory in use (2 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 333 colls, 0 par 0.004s 0.002s 0.0000s 0.0000s Gen 1 7 colls, 0 par 0.001s 0.001s 0.0001s 0.0003s TASKS: 4 (1 bound, 3 peak workers (3 total), using -N1) SPARKS: 126 (0 converted, 0 overflowed, 0 dud, 0 GC'd, 126 fizzled) INIT time 0.001s ( 0.000s elapsed) MUT time 0.928s ( 0.936s elapsed) GC time 0.005s ( 0.003s elapsed) EXIT time 0.001s ( 0.000s elapsed) Total time 0.935s ( 0.939s elapsed) Alloc rate 192,215,387 bytes per MUT second Productivity 99.4% of total user, 98.9% of total elapsed gc_alloc_block_sync: 0 whitehole_spin: 0 gen[0].sync: 0 gen[1].sync: 0 > ./BinSplit +RTS -s -N4 () 178,727,480 bytes allocated in the heap 3,506,488 bytes copied during GC 3,650,032 bytes maximum residency (7 sample(s)) 934,976 bytes maximum slop 12 MB total memory in use (1 MB lost due to fragmentation) Tot time (elapsed) Avg pause Max pause Gen 0 141 colls, 141 par 0.009s 0.002s 0.0000s 0.0001s Gen 1 7 colls, 6 par 0.003s 0.001s 0.0001s 0.0001s Parallel GC work balance: 38.80% (serial 0%, perfect 100%) TASKS: 10 (1 bound, 9 peak workers (9 total), using -N4) SPARKS: 126 (12 converted, 0 overflowed, 0 dud, 0 GC'd, 114 fizzled) INIT time 0.002s ( 0.002s elapsed) MUT time 2.104s ( 0.946s elapsed) GC time 0.012s ( 0.003s elapsed) EXIT time 0.001s ( 0.000s elapsed) Total time 2.119s ( 0.951s elapsed) Alloc rate 84,946,520 bytes per MUT second Productivity 99.3% of total user, 221.3% of total elapsed gc_alloc_block_sync: 600 whitehole_spin: 0 gen[0].sync: 9 gen[1].sync: 1073

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Haskell developer position in Jerusalem
by Yitzchak Gale 20 Aug '15

20 Aug '15

We have a position open for a Haskell developer. This is an on-site position at our development center in Jerusalem. You will be working on our enterprise customer-tailored content delivery products - see the "Products" tab on our home page - which are implemented (mostly) in Haskell. Search for Haskell on our "Careers" page for a fuller description of the position. Submit your CV to [jobs@suite-sol.com](mailto:jobs@suite-sol.com), but also feel free to contact me if you have any questions. Thanks, Yitz

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