- Haskell-Cafe - Haskell.org

Two new lectureships (assistant professorships) in Nottingham
by Graham Hutton 25 Oct '11

25 Oct '11

Dear all, We are currently seeking two new Lecturers (Assistant Professors) in Computer Science at the University of Nottingham, UK. These posts are available from 1st January 2012 on a fixed-term basis for three years. Applications from within the area of functional programming would be most welcome. For further details, see: http://www.nottingham.ac.uk/jobs/currentvacancies/ref/CE05936S The deadline for applications is 9th November 2011. Best wishes, Graham Hutton -- Prof Graham Hutton Functional Programming Lab School of Computer Science University of Nottingham, UK http://www.cs.nott.ac.uk/~gmh This message and any attachment are intended solely for the addressee and may contain confidential information. If you have received this message in error, please send it back to me, and immediately delete it. Please do not use, copy or disclose the information contained in this message or in any attachment. Any views or opinions expressed by the author of this email do not necessarily reflect the views of the University of Nottingham. This message has been checked for viruses but the contents of an attachment may still contain software viruses which could damage your computer system: you are advised to perform your own checks. Email communications with the University of Nottingham may be monitored as permitted by UK legislation.

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New rss maintainer
by Bas van Dijk 25 Oct '11

25 Oct '11

Hello, I've a small patch[1] that updates the rss package to the latest versions of its dependencies. (I'm trying to get the new hackage-server to build on ghc-7.2.1) However Bjorn Bringert told me he's no longer maintaining the package. He asked me to ask you if there's already a new maintainer. If not, does any one want to take over the package? Jeremy, maybe you? Otherwise I could take it over. I probably won't make lots of changes since I'm a bit swamped at the moment. Just updating it to the latest versions. Regards, Bas [1] http://code.haskell.org/~basvandijk/update_rss.dpatch

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Error when installing RSA (for yesod) with GHC 7.2.1
by Yves Parès 24 Oct '11

24 Oct '11

I'm using GHC 7.2.1 and cabal-install 0.8 (Cabal 1.8.0.2), and when "cabal install rsa" I got the error $ cabal install rsa Resolving dependencies... Configuring RSA-1.0.6.2... Preprocessing library RSA-1.0.6.2... Preprocessing executables for RSA-1.0.6.2... Building RSA-1.0.6.2... [1 of 1] Compiling Codec.Crypto.RSA ( Codec/Crypto/RSA.hs, dist/build/Codec/Crypto/RSA.o ) Codec/Crypto/RSA.hs:580:10: Duplicate instance declarations: instance Random Word8 -- Defined at Codec/Crypto/RSA.hs:580:10-21 instance Random Word8 -- Defined in System.Random cabal: Error: some packages failed to install: RSA-1.0.6.2 failed during the building phase. The exception was: ExitFailure 1 Apparently it's an instance being declared twice. However RSA hackage page states that it compiles under GHC 7.2: http://hackage.haskell.org/package/RSA

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lost in generics
by Rustom Mody 24 Oct '11

24 Oct '11

I need some help finding my way around the various generics libraries. My usage scenario is -- at least to start with -- the ASTs of programming languages. It appears to me that there are two generations of generics -- earlier there was generic haskell and strafunski Now there is uniplate and kure (and syb? -- not sure of its generation...) I get this impression because I saw a comment somewhat along these lines. And also the very first reference link on the strafunski webpage: http://www.haskell.org/haskellwiki/Applications_and_libraries/Generic_progr… viz http://www.cs.vu.nl/Strafunski/ seems to be dead. So I am wondering whether strafunski is still under development or is it defunct? The following paras from http://www.cs.uu.nl/research/techreps/repo/CS-2008/2008-010.pdf The current status of generic programming in Haskell is comparable > to the lazy Tower of Babel preceding the birth of Haskell > in the eighties [Hudak et al., 2007]. We have many single-site languages > or libraries, each individually lacking critical mass in terms > of language/library-design effort, implementations, and users. > Although generic programming has been used in several applications, > it has few users for real-life projects. This is understandable. > Developing a large application takes a couple of years, and > choosing a particular approach to generic programming for such a > project involves a risk. Few approaches that have been developed > over the last decade are still supported, and there is a high risk that > the chosen approach will not be supported anymore, or that it will > change in a backwards-incompatible way in a couple of years time. > sound omninous :-) In general my question is: What is alive/active and what is alive/active and what is -- um -- moved-on-from. And of course which are easier and which more difficult to dig into. Thanks Rusi

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Re: [Haskell-cafe] thespian thoughts
by Simon Michael 24 Oct '11

24 Oct '11

Hi Alex. I'm testing thespian in rss2irc, FYI: http://joyful.com/darcsden/simon/rss2irc/browse/rss2irc.hs#L-114 . Maybe there's a better way to use it, but for now it brings me one extra thread and higher memory usage/leakage - an instance grew to 350M overnight where I'd normally see 50-100M. The leak may be in my code, but I haven't found it yet. Did you notice high memory usage when using thespian ? Whether or not I end up keeping it, it has influenced the ordinary thread-based manager for the better, eg see forkMonitoredIO which is like a poor man's monitor using exceptions rather than actor messages. Best, - Simon On Oct 12, 2011, at 8:44 AM, Simon Michael wrote: > Hi Alex, thanks for the reply (it didn't seem to reach haskell-cafe, if that matters) and the update on status. I passed over CloudHaskell as it seemed (a) over-complex for my needs and (b) not ready, eg not on hackage. I need something that will still permit cabal install rss2irc. But perhaps that's not far off. I'll look again more closely, at both. > > Best - Simon > > > On Oct 11, 2011, at 10:48 PM, Alex Constandache wrote: > >> Hi Simon, >> >> Sorry for the late reply. I no longer work on thespian, as there is >> another project, called Cloud Haskell which provides much more >> functionality than thespian (including Erlang style distributed >> computing). It is not available on Hackage, but it lives on Github at >> >> https://github.com/jepst/CloudHaskell >> >> Simon Peyton-Johnes himself seems to be associated with the project, >> so you should have a look at it. If it does not match your needs, feel >> free to hack thespian and send me a pull request on bitbucket. You are >> the second person who emailed about thespian in the last month, so >> maybe I should reconsider the decision to abandon it (which was >> motivated by my desire to avoid contributing to the insane >> fragmentation that plagues Hackage). >> >> --Alex >> >> On Sun, Oct 9, 2011 at 12:45 PM, Simon Michael <simon(a)joyful.com> wrote: >>> Hi Alexander, >>> I went looking for something to clean up rss2irc's thread management, and >>> your recently released thespian package looks like the simplest, most >>> practical actors/erlang/OTP-ish lib for haskell so far. Thanks! >>> I need to restart threads (actors) in a controlled way when they die or >>> hang. I think some of all of that is also part of Erlang/OTP, and maybe it's >>> already on your todo list. Here are some notes I made, for your interest and >>> in case you have any further thoughts. >>> I thought of adding some actor-transforming combinators like these: >>> -- | Spawn the specified action and restart it whenever it dies, unless >>> -- the restart frequency exceeds any of the given maximum frequencies in >>> -- which case throw an exception. >>> restart :: [Frequency] -> IO a -> IO Address >>> restart fs action = spawn $ do >>> setFlag TrapRemoteExceptions >>> let start times = [] >>> forever >>> t <- getCurrentTime >>> update start times >>> when (any fs exceeded by start times) throw error >>> worker <- spawn action >>> monitor worker >>> receive worker [Case _ -> return ()] >>> -- | Convert hangs to exceptions using a watchdog timer: spawn the >>> -- specified action under the control of a watcher which monitors it and >>> -- also kills it and throws an exception if the worker ever fails to >>> -- send (something) to the watcher within the specified interval. >>> watchdog :: Seconds -> (Address -> IO a) -> IO Address >>> watchdog t action = spawn $ do >>> watcher <- self >>> worker <- spawn $ action watcher >>> monitor worker >>> forever >>> receiveTimeout t [Case _ -> return () >>> Default -> throw error >>> ] >>> which I would use something like: >>> main = do >>> (feed, bot) <- ... >>> spawn $ do >>> reader <- restart [MaxPerHour 2] $ watchdog 60 $ feedReader feed bot >>> announcer <- restart [MaxPerHour 2] $ watchdog 60 $ ircAnnouncer bot >>> responder <- restart [MaxPerHour 2] $ watchdog 60 $ ircResponder bot >>> monitor reader >>> monitor announcer >>> monitor responder >>> setFlag TrapRemoteExceptions >>> receive [Case e :: RemoteException -> exitFailure (show e) -- one of the >>> above died or hung too frequently >>> ] >>> but the types aren't right. I'm not sure if these combinators are possible >>> with the current thespian api. Also they would complicate things, eg what is >>> the address of a restarted actor ? >>> On second thoughts it might be better if these features were built in to the >>> library. I imagine something like: >>> main = do ... >>> reader <- spawnWith [RestartSpec [MinInterval (minutes 5), MaxPerHour >>> 3, MaxPerWeek 6], Watchdog (seconds 60)] $ feedReader feed bot >>> feedReader = do >>> forever >>> poll feed, do stuff >>> resetWatchdog >>> What do you think ? >>> Best - Simon >> >> >> >> -- >> AC >> I used to have a signature, but now I don't. >> >> -----BEGIN PGP PUBLIC KEY BLOCK----- >> Version: BCPG v1.45 >> >> mQINBE2kb5sBEADO/4u9AVkyz+jEnhgYzfdJ2tIIxOfAL4rqx2jXbxeFVq7vyBRS >> vM+K8u2Xw2TBC0dXzNy9GiBf9qjZS1EGPPiIvTLsp5aIoQLsO7E6H6g7Z5eqijMC >> c4qhrnmWsxcOZv8s0iil6H6OXa/EQzP2M1DRmyU8W49Cvo+Jg9hHZGbvdqpNrmYZ >> ZV5cA9hTneAFe7wixfQ7GDu80dCELmwwWX2adVpeW5dyX0u42Bp7e263GU1wPWTY >> t5CTkrgvHkFu7Hu3SGt66Q95xvCkK/RFLJbKJyeuHOY3uIa6YWKtMCNPcFz9C520 >> D+MQElWU9xFssxXj626v/GhTGoOPKu948rRgZl5OrBJjzOqaGtrDxuT45qjBfYV2 >> pkVzkTD2/3WNQNZapdrwNjf/fgomUVBTbeow1zPEypg1LHdX2Y58M54l6hCxbcgy >> JHALDCnROoEPeupJfncIYkp54hL3MJCspPHJoBMHpwfXZgmTNNfEQE2LX4recZ/7 >> PRIAntZ6/MZjBH/1vGc+BcIT5S5Z2J1INeZkEscz3pSl5iR8wYE1VyBRreaQptmq >> DtIIc2qyRN+BwbF7T0zCdYB2MHW1PA0pS3r4k//K8bmEf1ThH7u9jYuKKANDCltI >> ariGvz5/CxmW1+JnkSZtwb8w+3qcaMgOGYJhyD6K6RlYqq2htkjteWSdOwARAQAB >> tDpBbGV4IENvbnN0YW5kYWNoZSAoYWxleCkgPGFsZXhhbmRlci50aGUuYXZlcmFn >> ZUBnbWFpbC5jb20+iQIcBBMBAgAGBQJNpHAsAAoJEHNeWOpiNrFPBbUP/RCJC7C/ >> 78g0lQ1mvOzmfWoZ/tc0RceZqnfYYhm8VbZ6oNT3G4s2b7T5NdGCWqL1hGYVHupM >> 6TB4KA2eW8/3xh+oxbdC70i1WQYyfE81oKTSfW2+kBqtPIXueTs9AJ5rRX4cpPBr >> 8cDTx6tjCe+Vew59hUQ8JxAzs32Ol5mGOf4wpHhS4Un1mJwO+as0kHJnsA15dXoI >> Moo15NiJL9y77+8u1T6tHbGLYT9J/paoWOglA02FQIdlOAmQdCNhjZ4HKCKmMKsn >> WwlctvORzH+VtIpF9oxBtu0n3pPAE3wU4GyyVtg27wa+LNg7CEVHhJ/m6QSoPRFa >> TLYhK7OP4bOPdWZZUM1En4mWQFnb2fyKDPUIjqtbMBP6dcZin0nwRxZzngdLcdpm >> Prz14F5aS1+NvZOXhkPevBC6xXOnLwEr+egyM0jMGPdE3YnqMKOVR3e6bGE/wvPy >> OKtebMhFqLy1Yg87p3IU3Tv0Y1WV8GVEZr5lYHkbgM3yIY/WlH+MO5I4j7YXUdXf >> gvMjOMOxZ4wG8QEfkpdpaBm6JcRAkf9gb7IgBiOmdtC/N8s02NWyjRchvb/kOz5C >> eSCm6WV07Yhzxm+XTn+L8VxSN5YwCsF7gwD+Mtmone5TdmHS+7JJtjiq8WIbQrv3 >> /cwj2+7pnh7F032s2TpoJw0Og5HqjakiIkzYiQI2BBMBAgAgBQJNpHAsApsPBosJ >> CAcDAgSVAggDBJYCAwEFiQM9P4AACgkQc15Y6mI2sU8rfRAAtBCtd+XVjuqR/Of4 >> vy8Ev6N1/naqg7zOOQzQXT5UNpuoHO+y4oIYDvjkhGlxK4fVeIUHTQvhXS/INqyX >> 3oCKXYrzrsAgrq5FVdkRPwUV6H52ik/ani+IoGP2u85Y10DTnPGQnMzVwtN9Z6/T >> m486XA460J4jCIrRMpm+OJDHN6xUkgZFXaMW+scQK4At2wwcNvuOp9I9T4HP3viy >> b4g5IVgTsSZZoCIlSEvch2jGbM4hXDnLPFfIdSDxxn91sRgcmkNxCtGvKMVTDGYK >> JBvJYKki+X/CXfKlPwxTqHHjEbm8+uLyLDL32d7XTiS+0q31XthrVnVummiyIVtp >> tVhaBeY0JjX6Umi8DeaUWmT1xOckMIXMoAZBGux94hyaeKNEsSYXKQeM7nAvbEf9 >> EYPwoG82qRj/NyxqVH/Cx2IM24OYfoW2HwtU9l3QCHkCK1txCd3PvcWIFoSbwvX5 >> 1wB8/TgdhY4VM5BEJTBHTd8YZ6qi2pHeu+RdZoSCCHqeZA2WmGFpNsxRvHqw0sow >> YyadDulJu8AWT1+K0DTIxa3YWYIjMV9a/1LV5+/b4xx6KLvIbgS5aWsMMqmdhxMR >> w1cQ8JtkUSBgx8XzZIXqbMZEIhUmGeTGFBm+dKv91vTvxcM0vrrKPzAgiobRL2EE >> 43JwGJtFoGAc4zoRBUcXoRzodkc= >> =9igb >> -----END PGP PUBLIC KEY BLOCK----- >

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Haskell in Munich 2
by Dr. Heinrich Hördegen 24 Oct '11

24 Oct '11

Dear all, last month's meeting of Haskellers in Munich was a success. Let's repeat it! We will meet on Wednesday, 26 Oct, at Cafe Puck at Cafe Puck (www.cafepuck.de) Everybody interested in Haskell or functional programming is cordially invited. If you can't make it this time, check out this site for other dates: http://www.haskell-munich.de See you on Wednesday, Heinrich Hördegen P.S.: Some hours ago, I send this message with a wrong date. The correct date is Wednesday, 26 Oct, 19h30. Sorry.

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hello Haskell
by R J 24 Oct '11

24 Oct '11

hey Haskell this is nuts http://www.business10i.com

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haskell-janitors (was Re: New rss maintainer)
by Conrad Parker 24 Oct '11

24 Oct '11

On 22 October 2011 22:52, Bas van Dijk <v.dijk.bas(a)gmail.com> wrote: > I released a new rss: > > http://hackage.haskell.org//package/rss-3000.2.0 > > It no longer requires old-time and is tested with the latest versions > of its dependencies. > > On 21 October 2011 17:34, Vincent Hanquez <tab(a)snarc.org> wrote: >> Perhaps, unless someone step up, it would be nice to move packages that have >> no maintainer anymore into a github organisation (haskell-janitors ?), > > Nice idea! However I think we should always strive for having a single > or a limited number of maintainers. Finally when nobody wants to take > over a package we can hand it over to haskell-janitors. I like the janitors idea because it is practical, and I also like the ideal world where every package has an active maintainer. How about we set up the haskell-janitors github group as Vincent suggests, with some basic rules like: * when you upload a package you put your name and email address in the maintainer field, with a comment saying that you are maintaining this package through the haskell-janitors group * anyone in the haskell-janitors group can upload a new version of a package which is maintained through the haskell-janitors group. When you do so you set (or prepend?) your name as maintainer. * if anyone anywhere ever gets keen to take exclusive maintenance of a project, to redesign it or whatever, they're welcome to take it out of haskell-janitors. Goals would be: * timely uploads (anyone can upload) * accountability (you put your name on it) * packages still have someone who can accept patches, answer questions etc. (you put your name on it) Conrad.

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Will changing associativity of enumerator's ($=) affect anyone? (also: enumerator mailing list)
by John Millikin 24 Oct '11

24 Oct '11

A user recently suggested changing the associativity of ($=) from [[ infixr 0 ]] to [[ infixl 1 ]]. This allows the following expressions to be equivalent: run $ enumerator $$ enumeratee =$ enumeratee =$ iteratee run $ enumerator $= enumeratee $$ enumeratee =$ iteratee run $ enumerator $= enumeratee $= enumeratee $$ iteratee Although this is technically a backward-incompatible change, I feel it's small enough that it could go in a minor release *if nobody depends on the current behavior*. So, if anybody using 'enumerator' will have code broken by this change, please speak up. If I don't hear anything in a week or so, I'll assume it's all clear and will cut the new release. ------------------------- Second, I was asked whether there's a mailing list for enumerator stuff. To my knowledge there isn't, so I started one on librelist. To subscribe and/or post, send an email to haskell.enumerator(a)librelist.com . Archives are available at http://librelist.com/browser/haskell.enumerator/ . I plan to make release announcements there (for releases not important enough for haskell-cafe), and it might be useful for general discussion.

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SpecConstr message while compiling
by Daniel Díaz Casanueva 23 Oct '11

23 Oct '11

Hi, cafe! I wrote a program and had the following message while compiling (with -O2): SpecConstr Function `addOc{v s6RL} [lid]' has four call patterns, but the limit is 3 Use -fspec-constr-count=n to set the bound Use -dppr-debug to see specialisations What it means? Is it bad? It only happens when compiling with -O2. addOc is a local function (defined in a where clause). If it helps, here is the definition: addOc x [] = [(x,1)] addOc x ((y,n):ys) = if x == y then (y,n+1) : ys else (y,n) : addOc x ys I want to know if there is something wrong or a I don't need to take care about this. Thanks in advance, Daniel Díaz.

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