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[ANN] random-shuffle package
by Manlio Perillo 20 Mar '09

20 Mar '09

I'm pleased to announce the availability of random-shuffle package. The cabalized package is available at http://haskell.mperillo.ath.cx/random-shuffle-0.0.2.tar.gz The code is based on http://okmij.org/ftp/Haskell/perfect-shuffle.txt Thanks to Oleg Kiselyov for sharing this! I have made some changes to Oleg code: - changed coding style to what seems to be a more common Haskell coding style - Used Int, instead of Integer, for the index type - Forced some strict evaluation. It was a trial and error effort (I'm not an expert), but results are very impressive. Example program and timings/memory usage, are on: http://hpaste.org/fastcgi/hpaste.fcgi/view?id=2600 NOTE: I don't plan to upload the package to Hackage, for the near future. I'm thinking to add some other functions that operate on lists, like Python random module (random.choice, random.sample), and the partitioning function I have posted the other day (although I'm not sure this is a generic useful function). However, in this case, the package name should be changed. I'm not sure it is a good idea to release a package that implements only one function (but I may be wrong). Feedbacks (on current random-shuffle and future additions) are welcomed. Regards Manlio Perillo

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Using cabal to build an exportable library?
by Justin Bailey 20 Mar '09

20 Mar '09

I've been following this instructions at http://www.haskell.org/haskellwiki/Calling_Haskell_from_C to build a Haskell library which I can call from a C program. I'd like to use cabal to do the build in the future. Are there any examples showing how to do it?

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server directory layout for cabal-install?
by Johannes Waldmann 20 Mar '09

20 Mar '09

Hello. I wonder what is the required layout of directories and files on a server that supplies packages for cabal-install. I figure 00-index.tar.gz contains the *.cabal files. (The cabal files have to be on the server as well, unpacked?) Each $dir/$foo.cabal (in the archive) contains a "Version:$ver" line, and then $dir/$foo-$ver.tar.gz must be on the server? Are there additional constraints on the $dir part? What is the syntax of the .cabal/config file? The standard entry is repos: hackage.haskell.org:http://hackage.haskell.org/packages/archive , where the thing between "repos:" and ":http" is just a symbolic name, and I can add more lines like that? Thanks, J.W.

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Query on list comprehension
by Melanie_Green 20 Mar '09

20 Mar '09

What are the limitations of list comprehension. I want to use listcomprehension to output the pattern below. So a mixture of a's and newline characters. The part im stuck at is creating arguments in the listcomprehension to stop at some point then execute next loop. Is it even possible to create the pattern below purely from list comprehension.Thankyou in advance. a aa aaa -- View this message in context: http://www.nabble.com/Query-on-list-comprehension-tp22573574p22573574.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Haskell Logo Voting has started!
by Eelco Lempsink 20 Mar '09

20 Mar '09

Hi there! I updated a couple of logo versions and ungrouped and regrouped the (former) number 31. Other than that, there was nothing standing in the way of the voting to begin imho, so I started up the competition. By now, I suppose everybody should have received their ballot. If you think you should have received it but didn't, please report it, I can resend the invitation. Also, for people not directly subscribed to the haskell-cafe mailing list, you can still send ballot requests until the end of the competition (March 24, 12:00 UTC). Make sure the message contains 'haskell logo voting ballot request' (e.g. in the subject). Depending on the winner of this voting round we can decide whether we need to continue with variations. Jared Updike already offered to donate a bit of time to help create several variations. But for now, good luck with sorting those options! :) -- Regards, Eelco Lempsink

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What unsafeInterleaveIO is unsafe
by Yusaku Hashimoto 20 Mar '09

20 Mar '09

Hello, I was studying about what unsafeInterleaveIO is.I understood unsafeInterleaveIO takes an IO action, and delays it. But I couldn't find any reason why unsafeInterleaveIO is unsafe. I have already read an example in http://www.haskell.org/pipermail/haskell-cafe/2009-March/057101.html says lazy IO may break purity, but I think real matter in this example are wrong use of seq. did I misread?

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Why do functions not inherit class when renamed?
by Duane Johnson 20 Mar '09

20 Mar '09

I'm not sure I understand what is going on here, but it seems to me that the following assignment of "mult = (*)" causes "mult" to lose out on some of the polymorphic behavior of (*). Is that right? If so, why? > Prelude Data.Function Data.List Data.Char> let sizeMult = (*) `on` > length > Prelude Data.Function Data.List Data.Char> sizeMult "Duane" "Johnson" > 35 > Prelude Data.Function Data.List Data.Char> let mult = (*) > Prelude Data.Function Data.List Data.Char> let sizeMult2 = mult `on` > length > > <interactive>:1:26: > Couldn't match expected type `Integer' against inferred type `Int' > In the second argument of `on', namely `length' > In the expression: mult `on` length > In the definition of `sizeMult2': sizeMult2 = mult `on` length > Prelude Data.Function Data.List Data.Char> Thanks, Duane Johnson http://blog.inquirylabs.com/

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curl w/ ghc-win32
by Sigbjorn Finne 20 Mar '09

20 Mar '09

Hi, there's a steady stream of people reporting that getting started with curl on Windows is cumbersome and tricky to get right. A legitimate complaint! :-) To hopefully help out a bit in that regard, I've put together some notes covering the steps reqd + made available a pre-packaged curl binary dist -- http://haskell.forkio.com/Home/curl-win32 enjoy.. :) --sigbjorn

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[ANN] random-stream package
by Manlio Perillo 19 Mar '09

19 Mar '09

Hi. I'm pleased to announce the availability of my random-stream package. The cabalized package is available at: http://haskell.mperillo.ath.cx/random-stream-0.0.1.tar.gz Note that I have not uploaded it on Hackage, and I do not plan to upload it in the near future, at least until I will repute the package mature enough. From package description: Portable interface for the operating system source of pseudo random data. Supported sources are Unix /dev/urandom, Win32 CryptGenRandom and OpenSSL pseudo random numbers generator. This package is based on idea from os.urandom implementation, in CPython. The idea is to view the system pseudo random generator as a stream of infinite random bytes. So, I have used a lazy bytestring, and unsafePerformIO/unsafeInterleaveIO. The underlying data is: newtype Stream = Stream L.ByteString and the constructor *is exposed*. The package configuration *must* be done using a flag to specify the "source" to use. As an example: runghc Setup.hs configure -O2 -fHAVE_URANDOM runghc Setup.hs configure -O2 -fHAVE_SSL runghc Setup.hs configure -O2 -fHAVE_WIN32_CRYPT If the flag is not specified, the compilation will fail. Note that Windows it not yet supported. The stream generator implements tha RandomGen interface. Some notes: 1) The system *pseudo* random generator is used. As an example, on Linux, /dev/random produces "true" random numbers, but it may block if there is not enough entropy in the system. More details on http://en.wikipedia.org/wiki//dev/random 2) When reading data, the lazy bytestring chunk size is used. The default chunk size, however, is fine when reading from a regular file, but may not be the best choice when reading pseudo random numbers. For SSL (and Windows) support, the chunk size can be easily changed; but for Unix support this seems to not be possible, unless I reimplement hGetContents. The Data.ByteString.Lazy module have an hGetContentsN function. Unfortunately it is not exposed. I find this annoying; is it possible to export the *N functions from Data.ByteString.Lazy.Internal? 3) I have tested the package on Debian Linux Etch, using GHC 6.8.2. Feedback will be appreciate. I not sure about some details. Usage example: module Main where import System.Random import System.Random.Stream gen = mkStream l :: [Int] l = randoms gen :: [Int] main = do print l Manlio Perillo

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Hoogling to no avail ...
by Galchin, Vasili 19 Mar '09

19 Mar '09

Hello, I need sleep briefly(1/2 seconds) in code that I have written. I tried searching for "sleep" and "wait" in Hoogle and either didn't get a hit or got something inappropriate. ?? Regards, Vasili

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