January 2012 - Haskell-Cafe

RoseTree + Data.Typeable.Zipper
by Sergey Mironov 08 Jan '12

08 Jan '12

Hi list! Could you please give me a quick example of navigating throw Data.Typeable.Zipper built on top of a Rose Tree? eg. (See ??? in the last line - is my question) {-#LANGUAGE TemplateHaskell, DeriveDataTypeable, TypeOperators #-} import Data.Typeable.Zipper data Tree k a = Tree { _rules :: [(k,Tree k a)] } deriving(Show, Typeable) $(mkLabelsNoTypes [''Tree]) atree = Tree [(1, Tree []), (2, Tree []), (3, Tree [(11, Tree [])])] moveToLeftmostChild :: (Typeable k, Typeable a) => Zipper1 (Tree k a) -> Zipper1 (Tree k a) moveToLeftmostChild z = moveTo ??? z Thanks, Sergey

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All the random packages
by Eugene Kirpichov 08 Jan '12

08 Jan '12

Hi, I came across the beautiful algorithm for O(1) generation of rational discrete distributions http://www.keithschwarz.com/darts-dice-coins/ and though it'd be fun to implement it in Haskell and put on Hackage, but then it turned out that there's about a dozen random number packages, so I'm not sure to which one to contribute, or better to roll out my own package and encourage authors of the other packages to reference it and fit under their interface. What do you think? Which random number packages are considered to be most mature or perhaps promising - i.e., contributing to which ones will bring the community the most benefit? Is there any effort on unifying them going on? -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

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OpenAL bindings?
by Jason Dagit 08 Jan '12

08 Jan '12

Hello, Looks like the repo [1] for the OpenAL bindings that Sven Panne created [2] is no longer available. I assume this is a result of The Great Server Outage of 2011 [3]. Do other bindings exist (I didn't see any on hackage, google, or the wiki [4])? I can import the source that is available on hackage into a github repo and hack from there, but I wanted to ask first: Is the source of this repo gone for good? As a side note, I have plenty of other repos and things on my plate so I'm not really interested in becoming the maintainer of this binding. Any OpenAL experts interested in taking it over? I know from experience that Sven appears to be MIA in the Haskell community these days. Thanks, Jason -- [1] http://darcs.haskell.org/packages/OpenAL/ [2] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OpenAL [3] http://www.haskell.org/pipermail/haskell-cafe/2011-February/088829.html [4] http://www.haskell.org/haskellwiki/OpenAL

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ANN: leapseconds-announced-2012
by Bjorn Buckwalter 08 Jan '12

08 Jan '12

Dear all, The International Earth Rotation and Reference Systems Service (IERS) recently announced[1] that a positive leap second will be introduced at the end of June 2012. Consequently I have updated the leapseconds-announced library[2]. The original announcement of leapseconds-announced can be found below. Best regards, Bjorn Buckwalter [1] http://hpiers.obspm.fr/eoppc/bul/bulc/bulletinc.dat [2] http://hackage.haskell.org/package/leapseconds-announced ---------- Forwarded message ---------- From: Bjorn Buckwalter <bjorn.buckwalter(a)gmail.com> Date: Sat, Jan 17, 2009 at 13:23 Subject: ANN: leapseconds-announced-2009 To: Haskell(a)haskell.org, haskell-cafe(a)haskell.org Dear all, I'm pleased to announce the upload of the leapseconds-announced package[1] to Hackage. leapseconds-announced contains a single module and a single function implementing the Data.Time.Clock.TAI.LeapSecondTable interface (type). The documentation[2] for Data.Time.Clock.TAI.LeapSecondTable says "No table is provided, as any program compiled with it would become out of date in six months" and with that I have no objections. However, I frequently find myself needing a LeapSecondTable for a quick-and-dirty one-off analysis or simulation of the present or past. In these cases I've lazily used "(const 33)" (or more recently: "(const 34)") as my LeapSecondTable. leapseconds-announced is a pragmatic, if imperfect, improvement over my past practices. It provides a LeapSecondTable with all leap seconds announced to date (hence the name). Once the IERS announces[3] another leap second the package will need an update and all code using it a recompile. While this precludes its use in long-running production applications it is eminently adequate for my one-off uses or for applications that can afford to recompile infrequently. While, in the words of the Data.Time.Clock.TAI documentation, "most people won't need this module" I hope it can be of utility to someone. Thanks, Bjorn Buckwalter [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/leapseconds-anno… [2] http://www.haskell.org/ghc/docs/latest/html/libraries/time/Data-Time-Clock-… [3] http://hpiers.obspm.fr/eoppc/bul/bulc/bulletinc.dat

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Re: [Haskell-cafe] Problems with libgmp on Amazon Linux
by Nicu Ionita 07 Jan '12

07 Jan '12

Am 07.01.2012 20:01, schrieb Nabil Alsharif: > Ahh your main issue is that --prefix should be /usr not /usr/lib.... > It would be best to reinstall libgmp with the correct prefix. Oh, thanks, I will try this.

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[ANNOUNCE] First release of crypto-conduit
by Felipe Almeida Lessa 07 Jan '12

07 Jan '12

Hello! I'm pleased to announce the first release of crypto-conduit [1]! The crypto-api [2] package provides APIs for many cryptographic operations, such as cryptographic hashes and block ciphers. This new crypto-conduit package allows you to use many of these operations with conduits [3], giving you safe I/O using constant memory and no leaks. As an example, here's how you could get the SHA1 hash a file: import Crypto.Conduit -- from crypto-conduit import Crypto.Hash.SHA1 (SHA1) -- from cryptohash import Data.Conduit -- from conduit import Data.Conduit.Binary (sourceFile) -- from conduit main = do hash <- runResourceT $ sourceFile "my-file" $$ sinkHash print (hash :: SHA1) The code snippet above, despite having only "sourceFile ... $$ sinkHash" on its core, guarantees that the file handle is not kept open and uses a constant amount of memory. Sweet! Please break this package! Although it comes with a test suite, it has just seen the light of the day. Cheers, =) [1] http://hackage.haskell.org/package/crypto-conduit [2] http://hackage.haskell.org/package/crypto-api [3] http://hackage.haskell.org/package/conduit -- Felipe.

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ANNOUNCE: DHD >>= UHac, April 20 - 22, Utrecht
by Sean Leather 07 Jan '12

07 Jan '12

Calling all Haskellers! To open 2012 and in celebration of the group's 3rd year of existence, the Dutch Haskell Users Group is happy to announce a new event that combines an informal conference and a hackathon. >>= >> >> >> >> >> >> >>= >>= >>= >>= *DHD >>= UHac* >>= >>= >>= >>= *April 20 - 22* >>= >>= >>= >>= *Utrecht* >>= >>= >>= >>= >> >> >> >> >> >> >>= >>= DHD >>= The Dutch HUG Day, or DHD, will be a half day of talks on anything Haskell-y or FP-ish. It will be held on Friday, April 20. >>= UHac >>= The Utrecht Hackathon, or UHac, will be a gathering of the community of enthusiastic Haskell hackers from around the world. It will start immediately following the DHD and continue to Sunday, April 22. >>= Call for Speakers >>= We are looking for speakers for the Dutch HUG Day. If you have something interesting to share, please email Sean Leather (leather(a)cs.uu.nl) See the website for more. >>= Website >>= For more information that will be continuously updated, see the event wiki page: *http://www.haskell.org/haskellwiki/DHD_UHac* Join us for a Haskell-y time in the Netherlands. We look forward to seeing you there! Sean Leather and Jurriën Stutterheim Organizers

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Motivation for having indexed access in Data.Map?
by Christoph Breitkopf 07 Jan '12

07 Jan '12

Hello, I wonder why Data.Map provides the indexed access functions: http://hackage.haskell.org/packages/archive/containers/latest/doc/html/Data… These functions seem rather out-of-place to me in the map api. The only use case I could think of so far would be to find the median, or in general n-th smallest key, but that does not seem sufficient reason (also, I think there are faster methods for that). Anything else? Regards, Chris

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Problems with libgmp on Amazon Linux
by Nicu Ionita 07 Jan '12

07 Jan '12

Hello, I saw [1] there is a lot of activity in the Haskell community regarding Amazon Web Services (AWS). As they allow an easy start [2], I decided to giv it a try and followed the procedure published by JP Moresmau [3] to install the Haskell Plattform on Amazon Linux (a minimal linux distribution maintained by Amazon), but with the new Haskell Platform, 2011.4.0.0 (and ghc 7.0.4). It seemed to work pretty well, with some problems when configuring HP, because although libgmp was already installed, it was not recognized. I installed the newer version 5.0.2 (from sources) [4], did some tricks (cp /usr/lib/lib/libgmp* /usr/lib), then configure worked and HP was built and installed. But then later I wanted to install the aws package (cabal install aws) and then the vector package could not be installed - again because of libgmp! Here are the last messages, followed by a ls of /usr/lib, where it's clear that the libraries are there: [ 4 of 30] Compiling Data.Vector.Internal.Check ( Data/Vector/Internal/Check.hs, dist/build/Data/Vector/Internal/Check.o ) [ 5 of 30] Compiling Data.Vector.Fusion.Stream.Monadic ( Data/Vector/Fusion/Stream/Monadic.hs, dist/build/Data/Vector/Fusion/Stream/Monadic.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... <command line>: can't load .so/.DLL for: gmp (libgmp.so: cannot open shared object file: No such file or directory) cabal: Error: some packages failed to install: vector-0.9.1 failed during the building phase. The exception was: ExitFailure 1 [ec2-user@ip-10-234-49-92 ~]$ ls -l /usr/lib/libgmp* -rw-r--r-- 1 root root 1175336 Jan 4 22:21 /usr/lib/libgmp.a -rwxr-xr-x 1 root root 915 Jan 4 22:21 /usr/lib/libgmp.la -rwxr-xr-x 1 root root 484673 Jan 4 22:21 /usr/lib/libgmp.so -rwxr-xr-x 1 root root 484673 Jan 4 22:21 /usr/lib/libgmp.so.10 -rwxr-xr-x 1 root root 484673 Jan 4 22:21 /usr/lib/libgmp.so.10.0.2 [ec2-user@ip-10-234-49-92 ~]$ I'm just asking here hoping that someone had already solved this problem. Or perhaps someone can explain how cabal ensures that a library is there. The error message - as it is - is meaningless, as the file exists and has read permissions for everybody. Thank you, Nicu [1] http://www.reddit.com/r/haskell/comments/o1u2g/deploying_a_haskell_app_to_a… [2] https://aws.amazon.com/free/ [3] http://jpmoresmau.blogspot.com/2011/04/install-ghc7-and-yesod-on-amazon-lin… [4] ftp://ftp.gnu.org/gnu/gmp/

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Package for QuickCheck instances
by Antoine Latter 06 Jan '12

06 Jan '12

Hi Haskell, I was writing some tests that involved a large number of quickcheck properties which don't ship with the library itself, so I thought I would package them all together and put the orphan instances on Hackage. Here's what I have so far: https://github.com/aslatter/qc-instances/tree/93a87fa06b5575ddcc12c2f9eb0f4… The policy would be to allow anything into to package which is a part of the Haskell Platform or is a GHC build library. Has anyone already done this? I didn't find anything from grepping the Hackage package list. Has anyone already talked about doing this sort of thing? Are their any non-obvious pitfalls (aside from the package eventually becoming a cesspool of CPP conditions)? Thanks, Antoine

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