- Haskell-Cafe - Haskell.org

Nico de Bruijn dies at 93
by S D Swierstra 20 Feb '12

20 Feb '12

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Re: [Haskell-cafe] Data.Array.Accelerate initialization timings
by Paul Sujkov 20 Feb '12

20 Feb '12

Yep. It doesn't help: generateArray1 n = Acc.use $ Acc.fromList (Acc.Z Acc.:. n*n*n) [0..n*n*n] still takes the same amount of time. I guess something's wrong elsewhere. On 20 February 2012 16:06, Alex Gremm <algremm(a)googlemail.com> wrote: > Hi Paul, > > even though I just started reading about Accelerate, it seems to me that > you didn't use the "use" method which according to [1] initiates > asynchronous data transfer from host to GPU. > > > Cheers, > Alex > > [1]: http://www.cse.unsw.edu.au/%7Echak/papers/acc-cuda.pdf > On 20/02/12 14:46, Paul Sujkov wrote: > > Hi everyone, > > > > since accelerate mail list seems to be defunct, I'm trying to ask > > specific questions here. The problem is: array initialization in > > Data.Array.Accelerate takes a 10x amount of time in contrast to both > > Data.Array and bare C++ CUDA array initialization. This can be due to > > Data.Array.Accelerate having two backends (however, it's own tests show > > that my nVidia card is CUDA-capable), but I'm not aware of how can I > > profile GPU to check whether it is used or not. Anyway, here's code: > > > > http://hpaste.org/64036 > > > > both generateArray (DIM3) and generateArray1 (DIM1) take the same amount > > of time to initialize array. I'd say the problem is in GPU memory > > copying time, but here's bare C++ code: > > > > http://hpaste.org/64037 > > > > which does exactly the same, but 10 times faster. I'm wandering what am > > I doing wrong and how to check if I really am. Thanks in advance if > > anyone can point me on my mistakes! > > > > -- > > Regards, Paul Sujkov > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Regards, Paul Sujkov

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Re: [Haskell-cafe] Data.Array.Accelerate initialization timings
by Paul Sujkov 20 Feb '12

20 Feb '12

Hi Alex, I've seen that method, but I don't see how can I use it for initialization purposes. It creates Acc (Array e i) from Array e i, but what should I do while I don't have Array yet? And when Array is already initialized, 'use' will transfer it to GPU memory which will add some extra timings, but won't optimize what I have at the moment. However, I'll try to use it somehow. Maybe I misunderstand the mechanics. Thanks a lot! On 20 February 2012 16:06, Alex Gremm <algremm(a)googlemail.com> wrote: > Hi Paul, > > even though I just started reading about Accelerate, it seems to me that > you didn't use the "use" method which according to [1] initiates > asynchronous data transfer from host to GPU. > > > Cheers, > Alex > > [1]: http://www.cse.unsw.edu.au/%7Echak/papers/acc-cuda.pdf > On 20/02/12 14:46, Paul Sujkov wrote: > > Hi everyone, > > > > since accelerate mail list seems to be defunct, I'm trying to ask > > specific questions here. The problem is: array initialization in > > Data.Array.Accelerate takes a 10x amount of time in contrast to both > > Data.Array and bare C++ CUDA array initialization. This can be due to > > Data.Array.Accelerate having two backends (however, it's own tests show > > that my nVidia card is CUDA-capable), but I'm not aware of how can I > > profile GPU to check whether it is used or not. Anyway, here's code: > > > > http://hpaste.org/64036 > > > > both generateArray (DIM3) and generateArray1 (DIM1) take the same amount > > of time to initialize array. I'd say the problem is in GPU memory > > copying time, but here's bare C++ code: > > > > http://hpaste.org/64037 > > > > which does exactly the same, but 10 times faster. I'm wandering what am > > I doing wrong and how to check if I really am. Thanks in advance if > > anyone can point me on my mistakes! > > > > -- > > Regards, Paul Sujkov > > > > > > _______________________________________________ > > Haskell-Cafe mailing list > > Haskell-Cafe(a)haskell.org > > http://www.haskell.org/mailman/listinfo/haskell-cafe > > -- Regards, Paul Sujkov

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Data.Array.Accelerate initialization timings
by Paul Sujkov 20 Feb '12

20 Feb '12

Hi everyone, since accelerate mail list seems to be defunct, I'm trying to ask specific questions here. The problem is: array initialization in Data.Array.Accelerate takes a 10x amount of time in contrast to both Data.Array and bare C++ CUDA array initialization. This can be due to Data.Array.Accelerate having two backends (however, it's own tests show that my nVidia card is CUDA-capable), but I'm not aware of how can I profile GPU to check whether it is used or not. Anyway, here's code: http://hpaste.org/64036 both generateArray (DIM3) and generateArray1 (DIM1) take the same amount of time to initialize array. I'd say the problem is in GPU memory copying time, but here's bare C++ code: http://hpaste.org/64037 which does exactly the same, but 10 times faster. I'm wandering what am I doing wrong and how to check if I really am. Thanks in advance if anyone can point me on my mistakes! -- Regards, Paul Sujkov

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11th GhentFPG meeting: Tuesday 20th of March at 19:30h. Location and program TBA shortly.
by Jeroen Janssen 20 Feb '12

20 Feb '12

(apologies if you receive multiple postings) Dear all, The date has been decided and the 11th GhentFPG meeting will take place on Tuesday, the 20th of March at 19:30h. Note that due to organizational issues, we will be moving to a different location (still in Ghent though!). The program and exact location will be communicated shortly. We have two talks lined up and thus have room for one extra lightning talk, so if you have something to talk about do not hesitate to contact one of the organizers! Kind Regards, The GhentFPG organizing committee.

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Disabling warning over ranges of source lines
by Thomas DuBuisson 20 Feb '12

20 Feb '12

Using GHC, is there any way to disable warnings (entirely or selectively) during a section of source code? I ask because of some Template Haskell that periodically generates unused code and I'd rather not see the warnings or rework the macros (beyond emitting some sort of "disable" and "re-enable" pragma which probably isn't in the AST now that I think about it). Cheers, Thomas

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Test suite sections of cabal
by Kazu Yamamoto 20 Feb '12

20 Feb '12

Hello, I recently started using test suite sections of cabal but it soon appeared very inconvenient to me. 1) test data files If I want to include test data files into package, I have to enumerate all test files since the usage of '*' is restricted. I just want to specify the top directory of test data files. Why does this restriction exist? 2) build-dependency I need to repeat all build-dependency of a library section to a test suite section. Specifying the library itself to build-dependency of a test suite section does not work. This violates the DRY philosophy. Any ideas to avoid this? Thanks. --Kazu

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Failing to find a function
by Jon Fairbairn 19 Feb '12

19 Feb '12

This is probably a failure of my search fu or some other mental lacuna, but is there already a definition of this function somewhere: \a b -> runKleisli $ (Kleisli a) <+> Kleisli b ? Hoogling for its type MonadPlus m => (a -> m b) -> (a -> m b) -> a -> m b doesn’t net me anything useful. -- Jón Fairbairn Jon.Fairbairn(a)cl.cam.ac.uk

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Re: [Haskell-cafe] "Best" FRP package for newbie
by Adam Duracz 19 Feb '12

19 Feb '12

Hi Arnaud, While not necessarily in line with the state of the art of FRP libraries, I can warmly recommend going through the parts of Paul Hudak's "Haskell School Of Expression" that cover the Functional Animation Library ("FAL", basically a light version of Fran). The book introduces FRP concepts gently and FAL is really nice to work with, at least when it comes to the type of code that is discussed in that book. Good luck! //Adam On Feb 17, 2012, at 12:00 , haskell-cafe-request(a)haskell.org wrote: > Hello, > I am interested in exploring more in depth FRP. I had a look at the wiki > page and started to explore "reactive" which looked promising at first > glance and backed by quite a few articles and tutorials, but 1) it did not > install properly on my haskell platform and 2) from the mailing-list > archives it seems to have died a couple of years ago. > > So my question is : What package would you recommend me to get my hands > dirty with FRP? I am mostly interested in things related to music and > network programming, if that matters. > > Thanks in advance for your help, > > Arnaud

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hackage down
by Ozgur Akgun 19 Feb '12

19 Feb '12

Hackage seems to be down: http://www.downforeveryoneorjustme.com/http://hackage.haskell.org Best, Ozgur

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Functor in terms of Arrow
by Tom Schouten 19 Feb '12

19 Feb '12

Dear HC, Does AFunctor below have a standard name? It's a generalization of the Functor class in terms of Arrow instead of (->): fmap :: Functor f => (i -> o) -> f i -> f o afmap :: Arrow a, AFunctor f => a i o -> a (f i) (f o) It pops up in less general form (AFunctor = []) in iterated functions (difference equations / state space models), where the arrow is the update function parameterized by state type: data Iter s i o = Iter ((s,i) -> (s,o)) instance Arrow (Iter s) More concretely: > afmap :: ((s,i) -> (s, o)) -> (s,[i]) -> (s,[o]) > afmap f (s,[]) = (s,[]) > afmap f (s0, i:is) = (sn, o:os) where > (s1, o) = f (s0,i) > (sn, os) = afmap f (s1, is) > f (s,i) = (s', s') where s' = s + i > is = [1,1,1,1,1] > os = afmap f (0,is) -- (5,[1,2,3,4,5]) Cheers, Tom

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empty fields are dropped in bytestring csv
by Tom Doris 18 Feb '12

18 Feb '12

the bytestring-csv package appears to have a bug whereby empty fields are dropped completely from the row, which is different to Text.CSV , which will return an empty field in the parse result. I'd argue this is a bug in bytestring-csv, anyone know whether this has been raised before, or know of a workaround? Prelude Data.Maybe Data.List Text.CSV.ByteString Data.ByteString.Char8> parseCSV $ pack "a,b,c\n1,2,3\n1,,9\n" Just [["a","b","c"],["1","2","3"],["1","9"]] -- the last row has two fields ^ Prelude Text.CSV> parseCSV "/tmp/err" "a,b,c\n1,2,3\n1,,9\n" Right [["a","b","c"],["1","2","3"],["1","","9"],[""]]

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"Best" FRP package for newbie
by Arnaud Bailly 18 Feb '12

18 Feb '12

Hello, I am interested in exploring more in depth FRP. I had a look at the wiki page and started to explore "reactive" which looked promising at first glance and backed by quite a few articles and tutorials, but 1) it did not install properly on my haskell platform and 2) from the mailing-list archives it seems to have died a couple of years ago. So my question is : What package would you recommend me to get my hands dirty with FRP? I am mostly interested in things related to music and network programming, if that matters. Thanks in advance for your help, Arnaud

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BayHac '12
by Mark Lentczner 18 Feb '12

18 Feb '12

Please join us for a weekend of Haskell hacking: BayHac '12 April 20th ~ 22nd, 2012 Hacker Dojo Mountain View, CA This year will be concurrent with UHac in Utrecht, and technology willing, we'll be liking up to share the Hac between the continents! Full details on the Haskell Wiki: http://www.haskell.org/haskellwiki/BayHac2012 - Mark

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ANN: unification-fd 0.6.0
by wren ng thornton 17 Feb '12

17 Feb '12

-------------------------------------------- -- unification-fd 0.6.0 -------------------------------------------- The unification-fd package offers generic functions for single-sorted first-order structural unification (think Prolog programming or Hindley--Milner type inference)[1][2]. I've had this laying around for a few years, so I figured I might as well publish it. An effort has been made to try to make this package as portable as possible. However, because it uses the ST monad and the mtl-2 package it can't be H98 nor H2010. However, it only uses the following common extensions which should be well supported[3]: Rank2Types MultiParamTypeClasses FunctionalDependencies -- Alas, necessary for type inference FlexibleContexts -- Necessary for practical use of MPTCs FlexibleInstances -- Necessary for practical use of MPTCs UndecidableInstances -- For Show instances due to two-level types -------------------------------------------- -- Changes (since 0.5.0) -------------------------------------------- * The kind of variables has been changed from *->* to *. Thus, the definition of MutVar is now exactly the free monad generated by t on v: data MutTerm v t = MutVar !v | MutTerm !(t (MutTerm v t)) This is a major API-breaking change, however it only affects the type level, and should only affect you if you're using the functions class-polymorphically or if you've defined your own variable types. -------------------------------------------- -- Description -------------------------------------------- The unification API is generic in the type of the structures being unified and in the implementation of unification variables, following the two-level types pearl of Sheard (2001). This style mixes well with Swierstra (2008), though an implementation of the latter is not included in this package. That is, all you have to do is define the functor whose fixed-point is the recursive type you're interested in: -- The non-recursive structure of terms data S a = ... -- The recursive term type type PureTerm = Fix S And then provide an instance for Unifiable, where zipMatch performs one level of equality testing for terms and returns the one-level spine filled with pairs of subterms to be recursively checked (or Nothing if this level doesn't match). class (Traversable t) => Unifiable t where zipMatch :: t a -> t b -> Maybe (t (a,b)) The choice of which variable implementation to use is defined by similarly simple classes Variable and BindingMonad. We store the variable bindings in a monad, for obvious reasons. In case it's not obvious, see Dijkstra et al. (2008) for benchmarks demonstrating the cost of naively applying bindings eagerly. There are currently two implementations of variables provided: one based on STRefs, and another based on a state monad carrying an IntMap. The former has the benefit of O(1) access time, but the latter is plenty fast and has the benefit of supporting backtracking. Backtracking itself is provided by the logict package and is described in Kiselyov et al. (2005). In addition to this modularity, unification-fd implements a number of optimizations over the algorithm presented in Sheard (2001)--- which is also the algorithm presented in Cardelli (1987). * Their implementation uses path compression, which we retain. Though we modify the compression algorithm in order to make sharing observable. * In addition, we perform aggressive opportunistic observable sharing, a potentially novel method of introducing even more sharing than is provided by the monadic bindings. Basically, we make it so that we can use the observable sharing provided by the previous optimization as much as possible (without introducing any new variables). * And we remove the notoriously expensive occurs-check, replacing it with visited-sets (which detect cyclic terms more lazily and without the asymptotic overhead of the occurs-check). A variant of unification which retains the occurs-check is also provided, in case you really need to fail fast for some reason. * Finally, a highly experimental branch of the API performs *weighted* path compression, which is asymptotically optimal. Unfortunately, the current implementation is quite a bit uglier than the unweighted version, and I haven't had a chance to perform benchmarks to see how the constant factors compare. Hence moving it to an experimental branch. These optimizations pass a test suite for detecting obvious errors. If you find any bugs, do be sure to let me know. Also, if you happen to have a test suite or benchmark suite for unification on hand, I'd love to get a copy. -------------------------------------------- -- Notes and limitations -------------------------------------------- [1] At present it does not appear amenable for higher-rank structural unification (a la HMF, MLF, or other System F type systems). The Dyna code from which this package was based had such features, though the previous implementation doesn't fit with the simplified model of unification used in this package. It's on my todo list, and if you have any suggestions, feel free to contact me. [2] At present it is only suitable for single-sorted (aka untyped) unification, a la Prolog. In the future I aim to support multi-sorted (aka typed) unification, however doing so is complicated by the fact that it can lead to the loss of MGUs; so it will likely be offered as an alternative to the single-sorted variant, similar to how the weighted path-compression is currently offered as an alternative. [3] With the exception of fundeps which are notoriously difficult to implement. However, they are supported by Hugs and GHC 6.6, so I don't feel bad about requiring it. Once the API stabilizes a bit more I plan to release a unification-tf package which uses type families instead, for those who feel type families are easier to implement or use. There have been a couple requests for unification-tf, so I've bumped it up on my todo list. -------------------------------------------- -- References -------------------------------------------- Luca Cardelli (1987) /Basic polymorphic typechecking/. Science of Computer Programming, 8(2):147--172. Atze Dijkstra, Arie Middelkoop, S. Doaitse Swierstra (2008) /Efficient Functional Unification and Substitution/, Technical Report UU-CS-2008-027, Utrecht University. <http://www.cs.uu.nl/research/techreps/repo/CS-2008/2008-027.pdf> Oleg Kiselyov, Chung-chieh Shan, Daniel P. Friedman, and Amr Sabry (2005) /Backtracking, Interleaving, and/ /Terminating Monad Transformers/, ICFP. <http://www.cs.rutgers.edu/~ccshan/logicprog/LogicT-icfp2005.pdf> Tim Sheard (2001) /Generic Unification via Two-Level Types/ /and Paramterized Modules/, Functional Pearl, ICFP. <http://web.cecs.pdx.edu/~sheard/papers/generic.ps> Tim Sheard & Emir Pasalic (2004) /Two-Level Types and/ /Parameterized Modules/. JFP 14(5): 547--587. This is an expanded version of Sheard (2001) with new examples. <http://web.cecs.pdx.edu/~sheard/papers/JfpPearl.ps> Wouter Swierstra (2008) /Data types a la carte/, Functional Pearl. JFP 18: 423--436. <http://www.cs.ru.nl/~wouters/Publications/DataTypesALaCarte.pdf> -------------------------------------------- -- Links -------------------------------------------- Homepage: http://code.haskell.org/~wren/ Hackage: http://hackage.haskell.org/package/unification-fd Darcs: http://community.haskell.org/~wren/unification-fd Haddock (Darcs version): http://community.haskell.org/~wren/unification-fd/dist/doc/html/unification… -- Live well, ~wren

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[haskell-cafe] Some reflections on Haskell
by Doug McIlroy 17 Feb '12

17 Feb '12

Kevin Jardine notices "the full Haskell ecosystem ... is huge", and laments the absence of "a sophisticated IDE to help manage" it. Being a small-code type, I don't personally enjoy IDE's, which are undeniably useful in big projects, at the cost of a whole lot more to learn about "programmering" in addition to programming. Nevertheless, I share Jardine's concern about the central problem. It is hard to find one's way in this ecosystem. It needn't be, as Java illustrates. To my mind Java's great contribution to the world is its library index--light years ahead of typical "documentation" one finds at haskell.org, which lacks the guiding hand of a flesh-and-blood librarian. In this matter, it seems, industrial curation can achieve clarity more easily than open source. (To avoid entanglement with social media, this comment is going to Haskell Cafe rather than Google+ where other comments reside.) Doug McIlroy

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Haskell implementation of a database?
by Vasili I. Galchin 17 Feb '12

17 Feb '12

Hello, I have been looking through Hackage database for a Haskell implementation of a database(not a binding) but couldn't find anything. Probably it was under my nose?? Vasili

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"Good" Java book? (not off-topic)
by Ivan Perez 17 Feb '12

17 Feb '12

Hi, cafe, I find myself in the unusual position of having to recommend a few books on Java to people who want to use it professionally. As the people demanding this live in Burundi, I can't really say "Learn Haskell". Odds are they won't find a job there if they don't use mainstream languages. Is there any book on Java that approaches the language in a way that doesn't make programmers impervious to FP and Haskell? Not meaning to insult anybody here, I too learned Java before Haskell. But I also think it made learning Haskell much more difficult. Cheers, Ivan.

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Command Line Tools for Xcode
by Lyndon Maydwell 17 Feb '12

17 Feb '12

Hi Café. Has anyone read the news at http://kennethreitz.com/xcode-gcc-and-homebrew.html? It looks like Apple is going to support a minimalist command-line based toolchain for Xcode called "Command Line Tools for Xcode" based on the OSX-GCC-Installer project. Would Haskell support this rather than requiring a full Xcode install? The requirement of Xcode has always struck me as quite onerous, however this weighs in at around 200M - Much nicer! I'm having issues logging in to the apple developer center at the moment and was wondering if anyone had tried it out. Thanks!

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Compressed Data.Map for more efficient RAM usage?
by Jeremy Shaw 16 Feb '12

16 Feb '12

Sometimes we want to store very large collection types in RAM -- such as a Data.Map or Data.IxSet. It seems like we could trade-off some speed for space savings by compressing the values in RAM. Lemmih has previously created compact-map: http://hackage.haskell.org/package/compact-map which mightybyte used to create: https://github.com/mightybyte/compact-ixset compact-map converts the Haskell values to a more compact binary representation. But could we do even better by compressing the bytestrings? Here is a useless implementation: http://hpaste.org/63836 That version compresses each value by itself. But, that is probably going to be worse RAM usage, not better. I think what we really need to do is to store a dictionary in CMap that is used to compress all the ByteString values. That way if the same string appears in 10000 entries, they can all be compressed using the same compression code. One question is, how much would this benefit us? As an experiment I tried compressing one checkpoint file for real world acid-state app that I am involved with. A checkpoint file contains binary data that is serialized by the SafeCopy library. And it is data that is currently store in an IxSet in RAM. The uncompressed checkpoint file is 115MB. The compressed checkpoint file is 26MB. A checkpoint file probably contains more redundancy than an equivalent compressed IxSet because in addition to the values it also includes version tags and other easily compressed data. But, those numbers do look promising. At the very least, they do not rule out the possibility of some big savings. I do not have time to explore this anymore. But I think it could be a fun project for someone to work on. ;) I imagine a prototype with a shared dictionary could be hacked up in a few days. A bit more work would be required to document it, memory profile it, etc. If done well, we should be able to reuse the incremental compression code in Data.Map, Data.Set, Data.IxSet, HiggsSet, and other places. But, just focusing on Data.Map is a good start. I will create a bug in this bug tracker that links back to this message, http://code.google.com/p/happstack/issues/list - jeremy

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Monadic bind fixity: do vs (>>)
by Michael Baikov 16 Feb '12

16 Feb '12

Most docs ([1], [2]) about do-notation syntactic sugar tends to describe following expressions as equivalent: "do { a; b; c }" and "a >> b >> c", but they are not: first one gets de-sugared into "a >> (b >> c)", second one is equivalent to "(a >> b) >> c", because (>>) is declared using infixl. This should not be a problem, monadic law of Associativity states that "(m >>= f) >>= g ≡ m >>= (\x -> f x >>= g)", but this leads to generating different Core output and may lead to different performance (and it does, do { Just 4 ; Just 4 ... } is about 2% faster than Just 4 >> Just 4 >> ... if compiled with -O0, but 13% slower when compiled with -O11) This also leads to lots of fun when your monad breaks Associativity law :) Is there any reasons except for those 13% speed gain for this? [1]: http://en.wikibooks.org/wiki/Haskell/do_Notation [2]: http://book.realworldhaskell.org/read/monads.html#monads.dot

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ANNOUNCE: system-filepath 0.4.5 and system-fileio 0.3.4
by John Millikin 16 Feb '12

16 Feb '12

Both packages now have much-improved support for non-UTF8 paths on POSIX systems. There are no significant changes to Windows support in this release. system-filepath 0.4.5: Hackage: http://hackage.haskell.org/package/system-filepath-0.4.5 API reference: https://john-millikin.com/software/haskell-filesystem/reference/system-file… system-fileio 0.3.4: Hackage: http://hackage.haskell.org/package/system-fileio-0.3.4 API reference: https://john-millikin.com/software/haskell-filesystem/reference/system-file… ----- In GHC 7.2 and later, file path handling in the platform libraries was changed to treat all paths as text (encoded according to locale). This does not work well on POSIX systems, because POSIX paths are byte sequences. There is no guarantee that any particular path will be valid in the user's locale encoding. system-filepath and system-fileio were modified to partially support this new behavior, but because the underlying libraries were unable to represent certain paths, they were still "broken" when built with GHC 7.2+. The changes in this release mean that they are now fully compatible (to the best of my knowledge) with GHC 7.2 and 7.4. Important changes: * system-filepath has been converted from GHC's escaping rules to its own, more compatible rules. This lets it support file paths that cannot be represented in GHC 7.2's escape format. * The POSIX layer of system-fileio has been completely rewritten to use the FFI, rather than System.Directory. This allows it to work with arbitrary POSIX paths, including those that GHC itself cannot handle. The Windows layer still uses System.Directory, since it seems to work properly. * The POSIX implementation of createTree will no longer recurse into directory symlinks that it does not have permission to remove. This is a change in behavior from the directory package's implementation. See http://www.haskell.org/pipermail/haskell-cafe/2012-January/098911.html for details and the reasoning behind the change. Since Windows does not support symlinks, I have not modified the Windows implementation (which uses removeDirectoryRecursive).

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Transactional memory going mainstream with Intel Haswell
by Ben 16 Feb '12

16 Feb '12

http://arstechnica.com/business/news/2012/02/transactional-memory-going-mai… would any haskell STM expert care to comment on the possibilities of hardware acceleration? best, ben

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GSoc-2012: Lock-free Data Structures
by Sergiu Ivanov 16 Feb '12

16 Feb '12

Hello, On Thu, Feb 16, 2012 at 5:40 AM, Ryan Newton <rrnewton(a)gmail.com> wrote: > I'm interested in mentoring any projects related to concurrent data > structure implementation. Is it too late to propose new projects? > > http://parfunk.blogspot.com/2012/02/potential-gsoc-haskell-lock-free-data.h… This project idea sounds very cool to me :-) Could you please suggest a starting point in approaching it? I cannot view the article [0], since I don't have an active ACM subscription. I've seen the link [1], so, probably, I could contribute some patches to it? I'm not sure whether this is good, but this is not the first project idea that grabs my attention, so, frankly, my principal goal now would be getting the hang of it. Had I had the time, I would have tried to contribute to all Haskell libraries I like (sigh) Sergiu [0] http://cacm.acm.org/magazines/2011/3/105308-data-structures-in-the-multicor… [1] https://github.com/rrnewton/haskell-lockfree-queue

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Behavior of -threaded in GHC 7.4.1?
by Michael Craig 16 Feb '12

16 Feb '12

Hi all, I'm debugging an issue with multithreading and FFI calls in 7.4.1. The code in question is the zeromq3-haskell library, which provides an FFI binding to ZeroMQ. A little background: ZeroMQ gives the programmer "contexts" and "sockets". Contexts are thread-safe and generally used one-per-process, but sockets and not thread-safe so they're generally used one-per-thread. Have a look at the code in this gist: https://gist.github.com/1829190 It's just a server that prints requests and replies with "Hello", and a client that sends the requests ["1", "2", ..., "10"] and prints the responses. Despite the fact that ZMQ sockets are not thread-safe, it was possible to compile and run this code with -threaded under 7.0.4. Using MVars or some other locking mechanism, it was even possible to use the same socket from multiple parallel threads. (As long as the socket was not actually used in parallel by multiple threads, all was well.) In 7.4.1, the code will only run if compiled without -threaded. With -threaded, it croaks with an "operation on non-socket" error, which generally refers to a socket that's either been closed or I've dug through the code in zeromq3-haskell and haven't found anything suspicious looking. Before I go digging into libzmq itself, can somebody assure me that nothing has changed in 7.4.1 with regard to -threaded or the FFI that might cause this breakage? Cheers, Mike Craig

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New GSoC on Concurrent Data Structures -- was: How do I get official feedback (ratings) on my GSoC proposal?
by Ryan Newton 16 Feb '12

16 Feb '12

Neat, thanks Johan! (I had no idea it was so easy to post to Reddit.) I also put the proposed project on the trac: http://hackage.haskell.org/trac/summer-of-code/ticket/1608 So feel free to contact me, interested students! Cheers, -Ryan On Thu, Feb 16, 2012 at 12:51 AM, Johan Tibell <johan.tibell(a)gmail.com> wrote: > On Wed, Feb 15, 2012 at 7:40 PM, Ryan Newton <rrnewton(a)gmail.com> wrote: >> I'm interested in mentoring any projects related to concurrent data >> structure implementation. Is it too late to propose new projects? >> >> >> http://parfunk.blogspot.com/2012/02/potential-gsoc-haskell-lock-free-data.h… > > Not all all. It's quite early in fact (I tried to get people to think > about this early on.) I'd also post it to the Haskell reddit to make > sure it gets a bit more exposure (it's kinda buried here in this > thread.) > > -- Johan

1 0

Undocumented cost-centres (.\) using auto-all, and SCC pragma not being honored
by Dan Maftei 16 Feb '12

16 Feb '12

> > 1 When profiling my code with -auto-all, my .prof file names some sub-expressions with a backslash. Cf. below. What are these? e_step e_step.ewords e_step.\ e_step.\.\ e_step.update_counts e_step.fwords My e_step function binds seven expressions inside a let, then uses them in two ugly nested folds. (Yes, very hackish) As you can see, three such expressions are named explicitly (ewords, fwords, and update_counts). But where are the rest? Further, perhaps the backslashes have something to do with the lambda expressions I am using in the two nested folds? 2. A related question: I tried using the SCC pragma instead of auto-all. I added it to all seven expressions inside the let, and to the nested folds. However, only two showed up in the .prof file! How come? Thanks ninestraycats

2 2

Re: [Haskell-cafe] Haskell-Cafe Tag (was: Optimizations and parallel execution in the IO for a small spellchecker)
by JP Moresmau 16 Feb '12

16 Feb '12

I was not aware that it was something a poster was supposed to do, but now I notice that while the messages I get from the list have [Haskell-Cafe] on their subject, the ones I post don't. The Haskell-Cafe info page (http://www.haskell.org/mailman/listinfo/haskell-cafe) does not mention that you should have that tag in the subject. I'm probably a uncouth Frenchman knowing nothing about netiquette, but surely the list software could add such a tag if it was required? JP On Wed, Feb 15, 2012 at 8:14 PM, Paul Sujkov <psujkov(a)gmail.com> wrote: > Sorry, I've forgotten to add a [Haskell-Cafe] tag for the message. > > > On 15 February 2012 19:33, Paul Sujkov <psujkov(a)gmail.com> wrote: >> >> Hi everyone, >> >> http://hpaste.org/63732 >> >> that's a very simple spellchecker application: it consumes standard Linux >> dictionary, reads a file, and prints out words from that file that are not >> on the dictionary. I have taken it from a little cross-language benchmark >> and used to benchmark existing hash table implementations available on >> Hackage (with one used in code being the best according to timings). The >> question is: can I go further and effectively execute lookup and (maybe) >> output (line 20 or line 26 in the snippet) in parallel? >> >> I'm not good at all with Haskell parallel packages; I've tried >> monad-parallel (naive implementation eats away all the memory available) and >> parallel (haven't tried Par monad yet), but the last dosn't seem to fit well >> with the IO operations. If anyone can give me any suggestions on how can I >> implement parallel execution, or any thoughts on further sequential >> optimizations, it would be deeply appreciated. >> >> -- >> Regards, Paul Sujkov > > > > > -- > Regards, Paul Sujkov > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > -- JP Moresmau http://jpmoresmau.blogspot.com/

4 4

How do I get official feedback (ratings) on my GSoC proposal?
by Greg Weber 16 Feb '12

16 Feb '12

Other than changing the status myself, how do I get a priority attached to my GSoC proposal?

4 6

Haskell Weekly News: Issue 215
by Daniel Santa Cruz 16 Feb '12

16 Feb '12

Welcome to issue 215 of the HWN, a newsletter covering developments in the Haskell community. This release covers the week of February 5 to 11, 2012. You can find the HTML version of this issue at: http://contemplatecode.blogspot.com/2012/02/haskell-weekly-news-issue-215.h… Quotes of the Week * nand': haskell has a few advantages in the industry that few other languages can offer. these will become more obvious as time goes on and programming is forced into a functional direction in general. * seo: What i do not realize is actually how you are now not really much more well-liked than you might be right now. You are so intelligent. You realize thus significantly in terms of this subject, produced me in my view consider it from so many numerous angles. Its like men and women are not interested unless it‚s one thing to do with Woman gaga! Your personal stuffs excellent. Always care for it up! * monochrom: Schrodinger's Klein glass bottle: before you look, the cat is inside or outside; after you look, it is inside and outside :) * cmccann: Ruby is a fine language if you're secretly a lisp programmer but want to hide behing perl and smalltalk so nobody catches you * mlh: nice quote -- quick, someone register it for posterity * something: somebody never said, naturally. * irene-knapp: I was going to take a famous quote and put it in lambdabot as my own but I couldn't decide on one * shachaf: getLine :: IO String contains a String in the same way that /bin/ls contains a list of files * edwardk: [unsafePerformIO] sounds like a good idea, its tempting, it makes life easy, for the first 2 lines of code. then you go to write the third and everything goes to shit * cmccann: Idiom brackets are where you consume a mixture of alcohol and Conor McBride papers until your vision gets blurry enough that you can't actually see the Applicative operators anymore. * Philippa: incidentally, if you think about this you're probably starting to image control flow that looks like it's a glyph for summoning cthulhu - and then realising that it's 3d and consists of 'towers'. Make sense? * c_wraith: also, "actual" reals is a funny thing to call a set that consists mostly of things that cannot be described. * NihilistDandy: I feel like a hipster whenever I talk programming with people at my school. I always have to preface discussions with "you've probably never heard of it" :/ * ion: Three lefts make two wrongs * elliott: Explicit recursion should generally be avoided. Also, general recursion should be explicitly avoided! * CodeWeaverX: I expect that Weird Untraceable Suitcases Full Of Bad could result from the program assuming such an operation is pure when it clearly isn't. * elliott: cmccann: the instances list haddock generates is now a thing of majesty edwardk: elliott: welcome to my world * mzero: functional programming has a property that is often lacking in other languages... at dinner last night we were discussing it, and I dubbed it: "The Princess Bride" property --- which is, that a piece of code means what you think it means * sclv: You have a problem and think "I'll use a hash function." Now you have intermittantly colliding problems. * monochrom: data Ph a = Ph -- the phantom monad ksion: Is that a new Star Wars prequel? ;) * user1151874: i already declare hp as int with value 3 now my problem is when i put "hp--", it shows error [...] but if i put "--hp", the result print is 3 not 2. * edwardk: thats my secret. really i don't write anything. i just let others do the work and upload it to hackage behind their backs Top Reddit Stories * Haskell as most mainstream non-mainstream language? The RedMonk Programming Language Rankings: February 2012 Domain: redmonk.com, Score: 45, Comments: 25 On Reddit: [1] http://goo.gl/xWHB8 Original: [2] http://goo.gl/REBXN * The future is parallel, and the future of parallel is declarative (Simon Peyton Jones) [RE: Escape From the Ivory Tower] Domain: yow.eventer.com, Score: 41, Comments: 5 On Reddit: [3] http://goo.gl/PJSlh Original: [4] http://goo.gl/zUKT5 * How Prelude avoids overlapping instances in Show Domain: brandon.si, Score: 32, Comments: 18 On Reddit: [5] http://goo.gl/qGPZK Original: [6] http://goo.gl/rC6qr * InfoQ: Yesod Web Framework (Michael's QCon talk) Domain: infoq.com, Score: 32, Comments: 12 On Reddit: [7] http://goo.gl/93SFv Original: [8] http://goo.gl/Xao7S * Search tree that does not require that items be sorted. Domain: twanvl.nl, Score: 28, Comments: 3 On Reddit: [9] http://goo.gl/R2yLD Original: [10] http://goo.gl/WGfcV * Reverse engineering the ZeroMQ wire protocol for ZMQHS Domain: xrl.tureus.com, Score: 27, Comments: 0 On Reddit: [11] http://goo.gl/UKIun Original: [12] http://goo.gl/oVstA * Announcing Yesod 0.10 - conduits, persistent 0.8, improved Coffeescript integration Domain: yesodweb.com, Score: 25, Comments: 12 On Reddit: [13] http://goo.gl/1RRJH Original: [14] http://goo.gl/KftN5 * Real World Haskell book site -- is it known to be down? If so how long has it been down and will it come back? Domain: book.realworldhaskell.org, Score: 24, Comments: 15 On Reddit: [15] http://goo.gl/GV6z2 Original: [16] http://goo.gl/RCxnT * What do Haskellers think of Rust? It's got lambdas and ADTs with C-style notation. Domain: rust-lang.org, Score: 24, Comments: 40 On Reddit: [17] http://goo.gl/a9bCB Original: [18] http://goo.gl/xAKHx * r/darcs - for discussing darcs and patch theory Domain: reddit.com, Score: 24, Comments: 8 On Reddit: [19] http://goo.gl/37ArD Original: [20] http://goo.gl/qQiaD * Will Haskell be the Smalltalk of functional programming? Domain: self.haskell, Score: 22, Comments: 54 On Reddit: [21] http://goo.gl/ZxmBN Original: [22] http://goo.gl/ZxmBN Top StackOverflow Questions * Abusing the algebra of algebraic data types - why does this work? votes: 53, answers: 4 Read on SO: [23] http://goo.gl/MyQRO * Recommended reading/tutorials to understand reactive-banana FRP library votes: 13, answers: 3 Read on SO: [24] http://goo.gl/hTPv6 * Safe modelling of relational data in Haskell votes: 12, answers: 2 Read on SO: [25] http://goo.gl/4bEXX * What are the definitions for >>= and return for the IO monad? votes: 12, answers: 3 Read on SO: [26] http://goo.gl/9jH2x * Basic Structure of a Haskell Program votes: 11, answers: 1 Read on SO: [27] http://goo.gl/3OcKg * GHC API - How to dynamically load Haskell code from a compiled module using GHC 7.2? votes: 11, answers: 2 Read on SO: [28] http://goo.gl/aYKZz * Lifting a higher order function in Haskell votes: 9, answers: 1 Read on SO: [29] http://goo.gl/JhmjK * How do you check the type of a local variable? votes: 8, answers: 5 Read on SO: [30] http://goo.gl/Ynfgv * Tail optimization guarantee - loop encoding in Haskell votes: 7, answers: 2 Read on SO: [31] http://goo.gl/PKqfq * Writing in pointfree style f x = g x x votes: 7, answers: 1 Read on SO: [32] http://goo.gl/EIFBw Until next time, Daniel Santa Cruz References 1. http://redmonk.com/sogrady/2012/02/08/language-rankings-2-2012/ 2. http://www.reddit.com/r/haskell/comments/ph4uq/haskell_as_most_mainstream_n… 3. http://yow.eventer.com/events/1004/talks/1055 4. http://www.reddit.com/r/haskell/comments/phnd3/the_future_is_parallel_and_t… 5. http://brandon.si/code/how-the-haskell-prelude-avoids-overlapping-types-in-… 6. http://www.reddit.com/r/haskell/comments/pel34/how_prelude_avoids_overlappi… 7. http://www.infoq.com/presentations/Yesod 8. http://www.reddit.com/r/haskell/comments/pjqpr/infoq_yesod_web_framework_mi… 9. http://twanvl.nl/blog/haskell/SemilatticeSearchTree 10. http://www.reddit.com/r/haskell/comments/pj6n7/search_tree_that_does_not_re… 11. http://xrl.tureus.com/black-box-reverse-engineering-zmq 12. http://www.reddit.com/r/haskell/comments/pcojs/reverse_engineering_the_zero… 13. http://www.yesodweb.com/blog/2012/02/release-0-10 14. http://www.reddit.com/r/haskell/comments/phxjo/announcing_yesod_010_conduit… 15. http://book.realworldhaskell.org/read 16. http://www.reddit.com/r/haskell/comments/pd79r/real_world_haskell_book_site… 17. http://www.rust-lang.org/ 18. http://www.reddit.com/r/haskell/comments/pewtc/what_do_haskellers_think_of_… 19. http://reddit.com/r/darcs 20. http://www.reddit.com/r/haskell/comments/pkv8g/rdarcs_for_discussing_darcs_… 21. http://www.reddit.com/r/haskell/comments/pczyz/will_haskell_be_the_smalltal… 22. http://www.reddit.com/r/haskell/comments/pczyz/will_haskell_be_the_smalltal… 23. http://stackoverflow.com/questions/9190352/abusing-the-algebra-of-algebraic… 24. http://stackoverflow.com/questions/9210412/recommended-reading-tutorials-to… 25. http://stackoverflow.com/questions/9234205/safe-modelling-of-relational-dat… 26. http://stackoverflow.com/questions/9244538/what-are-the-definitions-for-and… 27. http://stackoverflow.com/questions/9153574/basic-structure-of-a-haskell-pro… 28. http://stackoverflow.com/questions/9198140/ghc-api-how-to-dynamically-load-… 29. http://stackoverflow.com/questions/9243215/lifting-a-higher-order-function-… 30. http://stackoverflow.com/questions/9210311/how-do-you-check-the-type-of-a-l… 31. http://stackoverflow.com/questions/9149183/tail-optimization-guarantee-loop… 32. http://stackoverflow.com/questions/9169046/writing-in-pointfree-style-f-x-g…

1 0

GHC -WAll, -fwarn-unused-do-bind and Cabal
by JP Moresmau 15 Feb '12

15 Feb '12

I'm confused: I'm using GHC 7.0.2 and Cabal 1.10.1.0 with cabal-install 0.10.2. I use -Wall in my Cabal file. If I build a Haskell file with unused do binds, via the GHC API I get no warning, which is normal, since the doc states: The warnings that are not enabled by -Wall are ..., -fwarn-unused-do-bind .... But if I build my project through cabal it gives me the warning! Why is compiling with Cabal giving that extra warning that GHC on its own with the same flags doesn't give? Using --verbose on cabal build does not give any clue, no suspicious extra flag is passed on. Any pointer appreciated! -- JP Moresmau http://jpmoresmau.blogspot.com/

2 2

Optimizations and parallel execution in the IO for a small spellchecker
by Paul Sujkov 15 Feb '12

15 Feb '12

Hi everyone, http://hpaste.org/63732 that's a very simple spellchecker application: it consumes standard Linux dictionary, reads a file, and prints out words from that file that are not on the dictionary. I have taken it from a little cross-language benchmark and used to benchmark existing hash table implementations available on Hackage (with one used in code being the best according to timings). The question is: can I go further and effectively execute lookup and (maybe) output (line 20 or line 26 in the snippet) in parallel? I'm not good at all with Haskell parallel packages; I've tried monad-parallel (naive implementation eats away all the memory available) and parallel (haven't tried Par monad yet), but the last dosn't seem to fit well with the IO operations. If anyone can give me any suggestions on how can I implement parallel execution, or any thoughts on further sequential optimizations, it would be deeply appreciated. -- Regards, Paul Sujkov

1 1

Concurrency strategy for 2 threads and rare events
by JP Moresmau 15 Feb '12

15 Feb '12

Hello, I'm wondering what's the best strategy to use in the following scenario: - 2 threads - One perform some work that will take time, possibly go on forever - Another waits for user input (like commands from the keyboard) that affects thread 1 (causing it to stop, in the simplest case) I've read a bit on MVar and channels, but they seem to be a lot for cases where the reading thread block for input. In my case, I expect to have "something" that thread 2 updates when an event occur, and thread 1 checks it regularly. So thread 1 should not block, but should check "is there something" and there is, act on it, otherwise continue doing what it was currently doing. I suppose I could just tryTakeMVar on a MVar, but is there something more adapted to my needs? Thanks! -- JP Moresmau http://jpmoresmau.blogspot.com/

4 5

Re: [Haskell-cafe] Hackage 2 maintainership
by Duncan Coutts 15 Feb '12

15 Feb '12

On 14 February 2012 10:43, Kirill Zaborsky <qrilka(a)gmail.com> wrote: > I apologize, > But does hackage.haskell.org being down for some hours already has something > with the process of bringing up Hackage 2? No, completely independent. The server was down for a few hours (and I think restored in the morning by the sysadmin at Galois). It was while I was mirroring to the new test server, but I don't think that was the cause of the outage. Some people were joking that the old server didn't want to be retired and so was shutting down to prevent the mirroring :-) Duncan

1 0

[haskell-cafe] Some reflections on Haskell
by Doug McIlroy 15 Feb '12

15 Feb '12

Markus: "What about hoogle/hayoo and hackage?" Antoine: "Do you have any links to examples that we should imitate?" Hackage is notionally similar to the Java API documentation at http://www.oracle.com/technetwork/java/javase/documentation/ But Hackage "Documentation" pages typically only give syntax, while Java pages invariably summarize semantics. This makes a world of difference. The quality of the summaries bespeaks a lot of editorial attention above and beyond culling annotations from source code. Considerable care has been taken in describing the GHC library at http://www.haskell.org/ghc/docs/ but even there one can find absolute mystery entries like http://www.haskell.org/ghc/docs/latest/html/libraries/haskell98-2.0.0.1/Loc… Doug > It is hard to find one's way in this ecosystm. It needn't be, > as Java illustrates. To my mind Java's great contribution to the > world is its library index--light years ahead of typical > "documentation" one finds at haskell.org, which lacks the guiding > hand of a flesh-and-blood librarian. In this matter, it > seems, industrial curation can achieve clarity more easily than > open source.

4 3

Language Shootout
by Louis Wasserman 15 Feb '12

15 Feb '12

Out of curiosity, do we know why the Language Shootout has upgraded<http://shootout.alioth.debian.org/u64q/program.php?test=spectralnorm&lang=g…>to GHC 7.4.1, but still isn't using -fllvm for e.g. the spectral-norm benchmark? (It results in a nonnegligible speedup on my machine.) Louis Wasserman wasserman.louis(a)gmail.com http://profiles.google.com/wasserman.louis

2 1

Google Summer of Code 2012 Announced
by Johan Tibell 14 Feb '12

14 Feb '12

Hi all, Here's a heads-up that this year's Google of Code is kicking off. My experience from the last few years is that we can maximize the output we get from GSoC by being proactive and writing down semi-detailed explanations of what kind of projects we'd like to see, instead of letting the students pick themselves*. Here's three examples of such write-ups I did last year: http://blog.johantibell.com/2011/03/summer-of-code-project-suggestions.html Concretely: 1. Write down the project suggestions somewhere (e.g. on the wiki, your blog, etc). 2. Advertise the projects on haskell-cafe, reddit, twitter, Google+ 3. Profit. * The students tend to not know what makes a good GSoC project and often aim for something too difficult, like writing a new project from scratch instead of contributing to an old one. Contributing to widely used libraries or infrastructure usually results in * a larger benefit for the community, and * the students sticking around. My guess is that the student tend to stick around after the project is done if they contribute to infrastructure projects, as they'll see their stuff get used and will get feature requests/bug reports that will make them continue working on the project. -- Johan ---------- Forwarded message ---------- From: Carol Smith <carols(a)google.com> Date: Sat, Feb 4, 2012 at 8:43 AM Subject: Google Summer of Code 2012 Announced To: Google Summer of Code Announce < google-summer-of-code-announce(a)googlegroups.com> Hi all, We're pleased to announce that Google Summer of Code will be happening for its eighth year this year. Please check out the blog post [1] about the program and read the FAQs [2] and Timeline [3] on Melange for more information. [1] - http://google-opensource.blogspot.com/2012/02/google-summer-of-code-2012-is… [2] - http://www.google-melange.com/gsoc/document/show/gsoc_program/google/gsoc20… [3] - http://www.google-melange.com/gsoc/events/google/gsoc2012 Cheers, Carol -- You received this message because you are subscribed to the Google Groups "Google Summer of Code Announce" group. To post to this group, send email to google-summer-of-code-announce(a)googlegroups.com. To unsubscribe from this group, send email to google-summer-of-code-announce+unsubscribe(a)googlegroups.com. For more options, visit this group at http://groups.google.com/group/google-summer-of-code-announce?hl=en.

6 9

Building a Haskell project which depends on an old version of base
by Steven J. Murdoch 14 Feb '12

14 Feb '12

I'm trying to build a Haskell project[1] which appears to be dependent on an function in a old version of base (GHC.Handle.fillReadBuffer). I've downgraded to Haskell platform 2010.2.0.0 which comes with GHC 6.12.3 (installed by homebrew on MacOS X 10.6.8), and ghc-pkg appears to indicate the backwards compatible library for base is available: $ ghc-pkg list base /Users/ghc6/homebrew/Cellar/ghc/6.12.3/lib/ghc/package.conf.d base-3.0.3.2 base-4.2.0.2 /Users/ghc6/.ghc/i386-darwin-6.12.3/package.conf.d However, when I try to cabal build the package, I get the following error: $ cabal -v build Creating dist/build (and its parents) Creating dist/build/autogen (and its parents) Preprocessing executables for TorDNSEL-0.1.1... Building TorDNSEL-0.1.1... Building executable tordnsel... Creating dist/build/tordnsel (and its parents) Creating dist/build/tordnsel/tordnsel-tmp (and its parents) /Users/ghc6/homebrew/bin/ghc --make -o dist/build/tordnsel/tordnsel -hide-all-packages -fbuilding-cabal-package -package-conf dist/package.conf.inplace -i -idist/build/tordnsel/tordnsel-tmp -isrc -idist/build/autogen -Idist/build/autogen -Idist/build/tordnsel/tordnsel-tmp -optP-include -optPdist/build/autogen/cabal_macros.h -odir dist/build/tordnsel/tordnsel-tmp -hidir dist/build/tordnsel/tordnsel-tmp -stubdir dist/build/tordnsel/tordnsel-tmp -package-id HUnit-1.2.2.1-6237339c6ad5673d3cd8f82c4c7f6343 -package-id array-0.3.0.1-438000c197b51c147f229b54edbf632e -package-id base-3.0.3.2-260693a92016991a03206b5a55f6a411 -package-id binary-0.5.1.0-b72d4a82a5aecd9243ff0f50456b3d47 -package-id bytestring-0.9.1.7-64b858f95ff0dacc8acf396bb53cf4b9 -package-id containers-0.3.0.0-ee442470d8dcc9e45f31677c400c5379 -package-id directory-1.0.1.1-fa3418f21f42269537be694d5922dd6d -package-id mtl-1.1.0.2-336254fecf8a77054f76cb33671a5177 -package-id network-2.2.1.7-2eb3746f71ba30c3e4940b75df5ea8b8 -package-id stm-2.1.2.1-95639ea16e2e2cbf4accbabda98a1809 -package-id time-1.1.4-d9f7b7932dc3a4863006ed6b1d525856 -package-id unix-2.4.0.2-94ca14c8a73570f9d75aca642b4de0c6 -O -O2 -Wall -DVERSION="0.1.1-dev" src/tordnsel.hs -lcrypto [ 4 of 39] Compiling TorDNSEL.Util ( dist/build/tordnsel/tordnsel-tmp/TorDNSEL/Util.hs, dist/build/tordnsel/tordnsel-tmp/TorDNSEL/Util.o ) src/TorDNSEL/Util.hsc:143:23: Module `GHC.Handle' does not export `fillReadBuffer' src/TorDNSEL/Util.hsc:143:39: Module `GHC.Handle' does not export `readCharFromBuffer' src/TorDNSEL/Util.hsc:145:26: Module `GHC.IOBase' does not export `Buffer(..)' The flags to ghc indicate that base-3.0.3.2 is being requested, and the documentation for base-3.0.3.2 indicates that GHC.Handle.fillReadBuffer exists[2]. Can anyone explain why I am getting this error message? Could it be because Util is a .hsc rather than .hs file? In tordnsel.cabal I've made two changes: set Build-Depends to include "base>=2.0 && < 4" to tell ghc that I really want base-3 and removed -Werror from GHC-Options (to ignore the deprecation warnings). Otherwise it is as provided in this distribution[3]. Building manually has the same result (though oddly I get a deprecation warning from building the .hs files but not the .hsc file, which led to my suspicion about hsc being an issue. $ hsc2hs TorDNSEL/Util.hsc $ ghc -package-id base-3.0.3.2-260693a92016991a03206b5a55f6a411 --make TorDNSEL/Util.hs [1 of 3] Compiling TorDNSEL.DeepSeq ( TorDNSEL/DeepSeq.hs, TorDNSEL/DeepSeq.o ) TorDNSEL/DeepSeq.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. TorDNSEL/Util.hs:1:11: Warning: -#include and INCLUDE pragmas are deprecated: They no longer have any effect [2 of 3] Compiling TorDNSEL.Compat.Exception ( TorDNSEL/Compat/Exception.hs, TorDNSEL/Compat/Exception.o ) TorDNSEL/Compat/Exception.hs:1:0: Warning: Module `Prelude' is deprecated: You are using the old package `base' version 3.x. Future GHC versions will not support base version 3.x. You should update your code to use the new base version 4.x. [3 of 3] Compiling TorDNSEL.Util ( TorDNSEL/Util.hs, TorDNSEL/Util.o ) TorDNSEL/Util.hsc:143:23: Module `GHC.Handle' does not export `fillReadBuffer' TorDNSEL/Util.hsc:143:39: Module `GHC.Handle' does not export `readCharFromBuffer' TorDNSEL/Util.hsc:145:26: Module `GHC.IOBase' does not export `Buffer(..)' Thanks in advance, Steven. [1] https://gitweb.torproject.org/tordnsel.git [2] http://hackage.haskell.org/packages/archive/base/3.0.3.2/doc/html/GHC-Handl… [3] https://gitweb.torproject.org/tordnsel.git/blob/HEAD:/tordnsel.cabal

3 2

Subject: A universal data store interface
by Greg Weber 14 Feb '12

14 Feb '12

Hi Sergiu, Thanks you for your interest in that proposal. I rushed it off a year ago. Since then we have made a lot of improvements to Persistent and the library forms a basic building block for most Yesod users and other Haskellers. Persistent offers a level of type-safety and convenience not available elsewhere (except perhaps for libraries like acid-state that are limited to in-memory storage). That being said, there are still a lot of improvements that could be made. With the effort of a GSoC volunteer we could probably get it to the point of being the go-to data storage library for Haskellers, at least those planning on using the subset of backends (likely SQL) with great support. This proposal is vague and we would need to work with you to narrow things down a bit. I am biased, but I believe the Yesod project is one of the most compelling in the Haskell ecosystem. There are a lot of different ways a GSoC project could help make things even better besides improving the associated Persistent library, and we would really like to mentor at least one GSoC student. I would open more tickets for this in the system, but I am not sure how helpful it will be. It seems that we need to reach out to more students like yourself, but I am not sure how to do that unless I see messages like these first. Greg Weber

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Ranges over Rational.
by André Scholz 14 Feb '12

14 Feb '12

Hello, i stumbled upon the specification of the Enum instances of Floats, Doubles and Rationals. I understand the idea behind this specification for floating point numbers. But why was it also used for Rational? As Rationals are exact, it would make sense to use the same definition of ranges as used for Integers. The specification seems to nullify the difference between Rational and floating point types in this respect. I would consider this a, well, a mistake in the specification. Kind regards, André Scholz

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How to increase performance using concurrency for sequential producer-consumer problem
by John Lato 14 Feb '12

14 Feb '12

I would use bounded STM channels (from the stm-chans package) for communication; this would keep the producer from getting too far ahead of the converters. You'd need to tag items as they're produced (an Integer should be fine) also, and keep track of the tags. A TVar should suffice for that. The basic outline is that the producer writes to a channel. Each converter thread reads from that channel, and when it's finished, checks the output index TVar. If the converter's item index is equal to the current output index,the converter puts its value into an output channel and increments the output index. A final consumer reads from the output channel and processes each item in turn. Or instead of a bounded input channel, the producer could write to a TMVar. Which is better probably depends on the details of your production pattern. You certainly could use something like iteratee-stm or the conduits variant, but they wouldn't directly help with concurrency of converters, nor with synchronization. What they would give you is concurrency between the producer, converter, and consumer. Of course you could build your own converter step to work within that framework. John L. > Date: Mon, 13 Feb 2012 16:12:22 +0100 > From: Roel van Dijk <vandijk.roel(a)gmail.com> > Subject: [Haskell-cafe] How to increase performance using concurrency > for sequential producer-consumer problem > To: Haskell Caf? <haskell-cafe(a)haskell.org> > Message-ID: > <CABw4ky7Pu_RJSj5hQ_7GS_VTqv-dA4iYV0VhEY_J1YxxYBLyvg(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > Hello, > > I have a program which I believe can benefit from concurrency. But I > am wondering if the mechanisms I need already exist somewhere on > Hackage. > > Here is a sketch of my program, in literate Haskell: > >> module Problem where >> import Control.Monad ( forM_ ) > > The producer produces values. It blocks until there are now more > values to produce. Each value is given to a callback function. > >> type Producer a = (a -> IO ()) -> IO () > > The converter does some work with a value. This work is purely CPU and > it is the bottleneck of the program. The amount of work it has to do > is variable. > >> type Converter a b = a -> b > > The consumer does something with the value calculated by the > converter. It is very important that the consumer consumes the values > in the same order as they are produced. > >> type Consumer b = b -> IO () > > Dummy producer, converter and consumer: > >> producer :: Producer Int >> producer callback = forM_ [1..10] callback > >> converter :: Converter Int Int >> converter = (*10) > >> consumer :: Consumer Int >> consumer = print > > A simple driver. Does not exploit concurrency. > >> simpleDriver :: Producer a -> Converter a b -> Consumer b -> IO () >> simpleDriver producer converter consumer = producer (consumer . converter) > >> current_situation :: IO () >> current_situation = simpleDriver producer converter consumer > > Ideally I would like a driver that spawns a worker thread for each > core in my system. But the trick is in ensuring that the consumer is > offered results in the same order as they are generated by the > producer. > > I can envision that some kind of storage is necessary to keep track of > results which can not yet be offered to the consumer because it is > still waiting for an earlier result. > > Is there any package on Haskell that can help me with this problem? Or > do I have to implement it using lower level concurrency primitives? > > Regards, > Roel > >

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Some reflections on Haskell
by Kevin Jardine 14 Feb '12

14 Feb '12

https://plus.google.com/u/0/111705054912446689620/posts/DPdA2rUSQ6c Comments are welcome! Kevin

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How to increase performance using concurrency for sequential producer-consumer problem
by Roel van Dijk 14 Feb '12

14 Feb '12

Hello, I have a program which I believe can benefit from concurrency. But I am wondering if the mechanisms I need already exist somewhere on Hackage. Here is a sketch of my program, in literate Haskell: > module Problem where > import Control.Monad ( forM_ ) The producer produces values. It blocks until there are now more values to produce. Each value is given to a callback function. > type Producer a = (a -> IO ()) -> IO () The converter does some work with a value. This work is purely CPU and it is the bottleneck of the program. The amount of work it has to do is variable. > type Converter a b = a -> b The consumer does something with the value calculated by the converter. It is very important that the consumer consumes the values in the same order as they are produced. > type Consumer b = b -> IO () Dummy producer, converter and consumer: > producer :: Producer Int > producer callback = forM_ [1..10] callback > converter :: Converter Int Int > converter = (*10) > consumer :: Consumer Int > consumer = print A simple driver. Does not exploit concurrency. > simpleDriver :: Producer a -> Converter a b -> Consumer b -> IO () > simpleDriver producer converter consumer = producer (consumer . converter) > current_situation :: IO () > current_situation = simpleDriver producer converter consumer Ideally I would like a driver that spawns a worker thread for each core in my system. But the trick is in ensuring that the consumer is offered results in the same order as they are generated by the producer. I can envision that some kind of storage is necessary to keep track of results which can not yet be offered to the consumer because it is still waiting for an earlier result. Is there any package on Haskell that can help me with this problem? Or do I have to implement it using lower level concurrency primitives? Regards, Roel

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Poll: Have you heard of or used GHC External Core?
by James Fisher 13 Feb '12

13 Feb '12

Hi all: I'm conducting a poll on Haskellers.com to assess the community importance of GHC External Core. Here's the link: http://www.haskellers.com/poll/7 Thanks, James Fisher

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xattr takeover
by Deian Stefan 13 Feb '12

13 Feb '12

Hello, I've been trying to get in touch with the maintainer (CC'd) about the xattr package for about a month. There are quite a few memory leaks (among other issues) for which I have a patch (see [1]). I would like to push the new version to Hackage, but the etiquette for taking over a package is unclear. Any suggestions? Thanks, Deian [1] https://github.com/deian/libattr-hs

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Usefulness of abstracting data storage, WAS: A universal data store interface
by Tom Murphy 13 Feb '12

13 Feb '12

Mailing list thread split! The GSoC seems like it should have its own list thread, so I'm moving this other discussion: On 2/13/12, Paul R <paul.r.ml(a)gmail.com> wrote: >> The most proeminent example is probably PostgreSQL, which is an >> incredibly strong product with high SQL power. But as soon as you access >> it through the ActiveRecord or Persistent API, it gets turned into >> a very limited store, with the SQL power of SQLITE or MongoDB. > > Tom> "Limited" /= "Worst", though [0]. > > Tom> The popularity of SQLite and "NoSQL" prove that sometimes a limited > Tom> feature set is worth the gains in abstraction. > > Tom> Definitely not for every project, of course. > > I don't dismiss MongoDB nor SQLite, they are great. But you probably > don't want to limit MongoDB to a SQL features set, and you don't want to > limit SQLite to a "NoSQL" interface, and you don't want to limit > PostgreSQL to a SQLite features set ... > > As you said, each of these stores has strenghs for particular needs and > weaknesses for others. Pick the one that best suits your project, and > use its full power, raw :) I agree about strengths and weaknesses of different data stores. However for my uses, I prefer Haskell Functors to any particular data store. The tool that helps me stay within Haskell the most is the one which I'll choose. Tom

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Happstack-state in non-happstack production apps
by Tom Murphy 13 Feb '12

13 Feb '12

Hi, Is it common to use happstack-state without happstack for real-world code (web or otherwise)? Thanks, amindfv / Tom

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Cannot understand liftM2
by Nicola Paolucci 13 Feb '12

13 Feb '12

Hi All, I'm loving learning Haskell quite a bit. It is stretching my brain but in a delightfull way. I've googled, I've hoogled but I haven't found a clear explanation for what exactly liftM2 does in the context below. Using the cool lambdabot "pointless" utility I found out that: > \x -> snd(x) - fst(x) is the same as: > liftM2 (-) snd fst I like the elegance of this but I cannot reconcile it with its type. I can't understand it. I check the signature of liftM2 and I get: Prelude> :t liftM2 Prelude> liftM2 :: (Monad m) => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r Can someone help me understand what's happening here ? What does a Monad have to do with a simple subtraction ? What is actually the "m" of my example ? I am sure if I get this I'll be another step closer to illumination ... Thanks, Nick

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ANNOUNCE: Registration open for DHD >>= UHac, April 20 - 22, Utrecht
by Sean Leather 13 Feb '12

13 Feb '12

We are happy to open registration to all. If you're interested in checking out some neat talks or hacking on cool Haskell projects, reserve your spot today! http://www.haskell.org/haskellwiki/DHD_UHac We are still looking for speakers for the Dutch HUG Day. Please consider sharing your latest new project or toy. It doesn't have to be research. It doesn't even have to be done. Just email Sean Leather (leather(a)cs.uu.nl) with your idea, and we'll talk about it. Also, the wiki has been updated with a lot more information since that last announcement. We'll continue to add more. Let us know if you have any questions. >>= >> >> >> >> >> >> >>= >>= >>= >>= DHD >>= UHac >>= >>= >>= >>= April 20 - 22 >>= >>= >>= >>= Utrecht >>= >>= >>= >>= >> >> >> >> >> >> >>= Sean Leather and Jurriën Stutterheim Organizers

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Stable pointers: use of cast to/from Ptr
by Yves Parès 13 Feb '12

13 Feb '12

Hello, According to the documentation ( http://hackage.haskell.org/packages/archive/base/4.5.0.0/doc/html/Foreign-S…) StablePtrs aims at being opaque on C-side. But they provide functions to be casted to/from regular *void**'s. Does that mean if for instance you have a StablePtr CInt you can cast it to Ptr () and alter it on C-side? void alter(void* data) { int* x = (int*)data; *x = 42; } -------------------------------------------------- -- using 'unsafe' doesn't change anything. foreign import ccall safe "alter" alter :: Ptr () -> IO () main = do sptr <- newStablePtr (0 :: CInt) deRefStablePtr sptr >>= print alter (castStablePtrToPtr sptr) -- SEGFAULTS! deRefStablePtr sptr >>= print freeStablePtr sptr But I tried it, and it doesn't work: I got a segfault when 'alter' is called. Is it normal? Does this mean I can only use my pointer as opaque? (Which I know to be working, as I already got a C function call back into Haskell and pass it the StablePtr via a 'foreign export') But in that case, what is the use of castStablePtrToPtr/castPtrToStablePtr, as you can already pass StablePtrs to and from C code? Thanks!

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