- Haskell-Cafe - Haskell.org

Polymorphic function over pairs of maybes.
by Edward Amsden 06 Jan '11

06 Jan '11

Hello all: I'd like to right a function that could take a structure with type (random example): (Int, (String, (Int, Int))) and another where each individual value is a Maybe of the corresponding type, for example: (Maybe Int, (Maybe String, (Maybe Int, Maybe Int))) and perform a fromMaybe using the values to produce a new value with the original types. The catch is, I'd like to be able to do that for an n-deep structure with any type, without having to write a separate function for them. I'm not even sure that this is possible, but perhaps someone could explain how it is or isn't? -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com

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Odd profiling results
by Erik de Castro Lopo 06 Jan '11

06 Jan '11

Hi all, I do some work on Ben Lippmeier's DDC compiler and when profiling DDC compiling a program with 11 source code files (much like ghc --make), we get a memory usage graph like this: http://www.mega-nerd.com/tmp/ddc-heap-usage-20101231.png We have no particular problem with the 11 peaks (one for each source file) but wonder what the hell is going on in the periods when the memory usage is flat. On a similar run the RTS reports that GC time was less than 10% of total runtime. This profiling information was captured on Debian on x86-64 system where DDC was compiled using ghc-6.12.1 (Debian package). Clues? Thanks, Erik -- ---------------------------------------------------------------------- Erik de Castro Lopo http://www.mega-nerd.com/

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Re: [Haskell-cafe] What's the best seed for random API ?
by Robert Clausecker 06 Jan '11

06 Jan '11

It probably is, but definitly not portable. Try to find /dev/urandom under Windows.

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What's the best seed for random API ?
by z_axis 06 Jan '11

06 Jan '11

picoSec :: IO Integer picoSec = do t <- ctPicosec `liftM` (getClockTime >>= toCalendarTime) return t rollDice :: Int -> IO Int rollDice n = do ps <- picoSec return $ (take 1 $ randomRs (1,n) $ mkStdGen $ fromInteger ps) !! 0 The above code uses `ctPicosec` as seed. Is it better to use the output of /dev/urandom as seed ? Sincerely! ----- e^(π.i) + 1 = 0 -- View this message in context: http://haskell.1045720.n5.nabble.com/What-s-the-best-seed-for-random-API-tp… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Choosing a type-class instance based on the context
by Cristiano Paris 06 Jan '11

06 Jan '11

Hi all, I was reading: http://www.haskell.org/haskellwiki/GHC/AdvancedOverlap and I became curious. Playing with the code I started to find a way to say: instance Show a => ShowPred a HTrue instead of enumerating all the instances, mirroring those of the Show class: instance ShowPred Int HTrue instance ShowPred Bool HTrue instance ShowPred a flag => ShowPred [a] flag Would that be possible? My opinion is that's not possible but I want to hear what the type-system gurus think about it. Thanks, -- Cristiano GPG Key: 4096R/C17E53C6 2010-02-22 Fingerprint = 4575 4FB5 DC8E 7641 D3D8 8EBE DF59 B4E9 C17E 53C6

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Experiences with Intel's manycore lab?
by Michael Lesniak 05 Jan '11

05 Jan '11

Hello, does anyone have experiences (good/bad) or some good-to-know knowledge about Intel's manycore lab, which supposedly has GHC 6.13 installed[1]? Regards, Michael [1] http://software.intel.com/en-us/blogs/2010/10/14/prerelease-ghc-and-haskell… -- Dipl.-Inf. Michael C. Lesniak University of Kassel Programming Languages / Methodologies Research Group Department of Computer Science and Electrical Engineering Wilhelmshöher Allee 73 34121 Kassel Phone: +49-(0)561-804-6269

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thread safety, IO arrays, and IO refs
by Eric Stansifer 05 Jan '11

05 Jan '11

Hello, I wish to use a mutable array in multiple threads. Can IO arrays be used in any thread, or only the thread they are created in? (So if I create an IO array in one thread, pass it to another via an MVar, can I read / edit it in that other thread?) Similarly about IORefs... can they be used across threads? (Obviously I will need to manage locking myself if I use an IO ref or array.) Are there any good resources on concurrency in Haskell that would answer questions similar to these? I've been learning by reading the ghc library documentation, but of course it's not comprehensive. The online tutorials I've seen aren't so in-depth, either. Thanks, Eric

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[ANNOUNCE] Etage 0.1.7, a general data-flow framework
by Mitar 05 Jan '11

05 Jan '11

Hi! I am glad to announce a new version of Etage, a general data-flow framework. Now it supports also GHC 7.0 and not just GHC head and because of this also Hackage successfully generates documentation so it is easier to understand the framework. http://hackage.haskell.org/package/Etage Feel free to test it and provide any feedback Mitar

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Network.Curl and thread safety
by Iustin Pop 05 Jan '11

05 Jan '11

Hi all, I'm not able to find out how one can use Network.Curl with the threaded runtime safely. I have this simple example: import Network.Curl import Control.Concurrent import Control.Concurrent.MVar getUrl :: (Monad m) => String -> IO (m String) getUrl url = do (code, body) <- curlGetString url [CurlSSLVerifyPeer False, CurlSSLVerifyHost 0, CurlTimeout 15, CurlConnectTimeout 5] return $ case code of CurlOK -> return body _ -> fail $ "Curl error for " ++ url ++ " error " ++ show code runGet :: String -> MVar (Maybe String) -> IO () runGet url mv = do body <- getUrl url putMVar mv body main = withCurlDo $ do let urls = replicate 10 "https://google.com/" mvs <- mapM (\_ -> newEmptyMVar) urls mapM_ (\(mv, url) -> forkIO (runGet url mv)) $ zip mvs urls mapM (\mv -> takeMVar mv >>= print) mvs threadDelay 10000000 When using curl linked with GnuTLS and running it with the multi-threaded runtime, it fails immediately with: $ ./main main: ath.c:193: _gcry_ath_mutex_lock: Assertion `*lock == ((ath_mutex_t) 0)' failed. Aborted (core dumped) Reading the Network.Curl docs, it seems that using withCurlDo should be enough to make this work (although I'm not sure about the description of the function and "no forking or lazy returns"). Using Network.Curl built against the OpenSSL headers does successfully retrieve all URLs, but fails a bit later (during the threadDelay, probably in GC) again with segmentation fault in libcurl.4.so. I've tried changing forkIO to forkOS, but still no luck, with either SSL library. Any ideas what I'm doing wrong? regards, iustin

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Re: [Haskell-cafe] [Haskell] ANNOUNCE: haskell-src-meta 0.3
by Ben Millwood 04 Jan '11

04 Jan '11

It seems I wasn't subscribed to haskell-cafe so this reply didn't get through (sorry for sending this twice, Felipe). I've now subscribed with delivery turned off for -cafe so if you want me to read a response be sure to address me directly :) On Tue, Jan 4, 2011 at 5:08 AM, Ben Millwood <haskell(a)benmachine.co.uk> wrote: > On Tue, Jan 4, 2011 at 4:02 AM, Felipe Almeida Lessa > <felipe.lessa(a)gmail.com> wrote: >> On Tue, Jan 4, 2011 at 1:49 AM, Ben Millwood <haskell(a)benmachine.co.uk> wrote: >>> haskell-src-meta is a package originally written by Matt Morrow to >>> provide a translation from the syntax tree provided by >>> haskell-src-exts to template haskell syntax. Essentially this allows >>> TH code to be parsed from a string, and is used in several quasiquoter >>> libraries. >> >> Are the purposes of haskell-src-meta and haskell-src-exts-qq the same? >> What are the main differences? >> >> Cheers! =) >> >> -- >> Felipe. >> > > If you look at the source for Language.Haskell.Exts.Translate from > haskell-src-exts-qq [1], you can see that it was actually taken from > an earlier version of haskell-src-meta, presumably during the long > period for which HSM was not maintained. I guess you could say that it > inlined the key parts of haskell-src-meta into its codebase, but I > hope that the maintainer can feel more confident about using the > haskell-src-meta package as a dependency now. > > My understanding of the *purpose* of haskell-src-exts-qq is that it is > for easily generating ASTs for use with haskell-src-exts, whereas > haskell-src-meta is for generating ASTs for use with template haskell. > > [1] http://hackage.haskell.org/packages/archive/haskell-src-exts-qq/0.3.0/doc/h… >

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