May 2008 - Haskell-Cafe

Re: [Haskell] Announce: hback - dual n-back memory game (0.0.2)
by Don Stewart 30 May '08

30 May '08

wojtowicz.norbert: > I'm pleased to publically announce a little project I've worked on. > Based on a recent research paper [0] that claims fluid intelligence > could be improved by training working memory, I wrote up a dual n-back > test memory game in Haskell and gtk2hs. This is still essentially an > alpha release: all comments are most welcome. > > Original post (includes gameplay instructions): > http://pithyless.com/blog/2008/05/18/hback-haskell-n-back-memory-game/ > > Updated version (overhaul of game with some feature updates): > http://pithyless.com/blog/2008/05/30/hback-0_0_2/ > > Cabal file can be found on hackage: > http://hackage.haskell.org/packages/archive/hback/0.0.2/hback-0.0.2.tar.gz > > [0] http://www.pnas.org/cgi/content/abstract/0801268105v1 Awesome! Is this the first real implementation of the game described in the paper? If so, that's a bit of a coup. Good work by the GTK team that has made these gui things in Haskell so easy. -- Don

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Seen on HCAR: CoreErlang library
by Dimitry Golubovsky 30 May '08

30 May '08

Hi, I have just spotted the item 5.4.3 on the recently issued HCAR: CoreErlang is a Haskell library which consists of a parser and a pretty-printer for the intermediate language used by Erlang. There is no e-mail of the developer (Henrique Ferreiro Garcia) shown on the report, so I am posting this on the mailing list. What is the current status of this Core Erlang library? I might be interested to use some parts of it in the Haskell to Erlang converter that I am currently experimenting with. Please contact me at golubovsky at gmail dot com. Thank you. -- Dimitry Golubovsky Anywhere on the Web

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Copying Arrays
by Tom Harper 30 May '08

30 May '08

I'm trying to implement some file I/O where I can read in a file to an array, but do so without having to know how much space I will need. (Before you suggest it, lists are too slow/space consuming.) I was thinking that one possible solution is to use a strategy used in dynamic arrays, where everytime you run out of space you double the capacity of the array. Trouble is, most arrays in Haskell would require you to traverse the entire array and copy each individual cell, which would make it worthless. Are there any low-level array types (MutableByteArray#, for example) that support a memcpy-like function where I could copy the entire array into the new one instead of copying it one value at a time? Is there another solution that I'm missing? -- Tom Harper MSc Computer Science '08 University of Oxford Mobile: +44 (0)7533 998 591 Skype: +1 949 273 4627 (harpertom)

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So how do people pronounce 'cabal' around here?
by Dan Piponi 30 May '08

30 May '08

In particular, which syllable gets the stress, and what are the lengths of the two vowels? Couldn't find anything in the FAQ (http://www.haskell.org/haskellwiki/Cabal/FAQ) -- Dan

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zlib, missing zlib.h
by Thomas Hartman 30 May '08

30 May '08

Tried to install http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zlib which is required for http://darcs.haskell.org/cabal-branches/cabal-1.4 which is required for cabal-install. Got the following error. apt-get installed zlibc on a stab in the dark, but same result. advice? thartman@thartman-laptop:~/haskellInstalls/smallInstalls/cabal-install/zlib-0.4.0.4>runghc Setup.hs configure Configuring zlib-0.4.0.4... thartman@thartman-laptop:~/haskellInstalls/smallInstalls/cabal-install/zlib-0.4.0.4>runghc Setup.hs build &>out thartman@thartman-laptop:~/haskellInstalls/smallInstalls/cabal-install/zlib-0.4.0.4>head out Preprocessing library zlib-0.4.0.4... Stream.hsc:74:18: error: zlib.h: No such file or directory Stream.hsc: In function 'main': Stream.hsc:254:0: error: 'z_stream' undeclared (first use in this function) Stream.hsc:254:0: error: (Each undeclared identifier is reported only once thartman@thartman-laptop:~/haskellInstalls/smallInstalls/cabal-install/zlib-0.4.0.4>

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ANNOUNCE: Haskell Communities and Activities Report (14th ed., May 2008)
by Janis Voigtlaender 30 May '08

30 May '08

On behalf of the many, many contributors, we are pleased to announce that the Haskell Communities and Activities Report (14th edition, May 2008) http://www.haskell.org/communities/ is now available from the Haskell Communities home page in PDF and HTML formats. Many thanks go to all the people that contributed to this report, both directly, by sending in descriptions, and indirectly, by doing all the interesting things that are reported. We hope you will find it as interesting a read as we did. If you haven't encountered the Haskell Communities and Activities Reports before, you may like to know that the first of these reports was published in November 2001. Their goal is to improve the communication between the increasingly diverse groups, projects and individuals working on, with, or inspired by Haskell. The idea behind these reports is simple: Every six months, a call goes out to all of you enjoying Haskell to contribute brief summaries of your own area of work. Many of you respond (eagerly, unprompted, and well in time for the actual deadline ;) ) to the call. The editor collects all the contributions into a single report and feeds that back to the community. When we try for the next update, six months from now, you might want to report on your own work, project, research area or group as well. So, please put the following into your diaries now: ---------------------------------------- End of October 2008: target deadline for contributions to the November 2008 edition of the HC&A Report ---------------------------------------- Unfortunately, many Haskellers working on interesting projects are so busy with their work that they seem to have lost the time to follow the Haskell related mailing lists and newsgroups, and have trouble even finding time to report on their work. If you are a member, user or friend of a project so burdened, please find someone willing to make time to report and ask them to `register' with the editor for a simple e-mail reminder in the middle of November (you could point us to them as well, and we can then politely ask if they want to contribute, but it might work better if you do the initial asking). Of course, they will still have to find the ten to fifteen minutes to draw up their report, but maybe we can increase our coverage of all that is going on in the community. Feel free to circulate this announcement further in order to reach people who might otherwise not see it. Enjoy! Andres Loeh and Janis Voigtlaender <hcar at haskell.org> -- Dr. Janis Voigtlaender http://wwwtcs.inf.tu-dresden.de/~voigt/ mailto:voigt@tcs.inf.tu-dresden.de

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HDBC with SQL Server / OBDC
by Morten Holm Pedersen 30 May '08

30 May '08

am trying to do a simple DB connection from Haskell to a SQL Server 2005 (on Windows obviously). The DSN name ("Nylon") works from C++ but when running the below example (or any other I can think of) ghci crashes. Does anyone know a resolution for this or where the problem can possible be ? GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help Loading package base ... linking ... done. Prelude> :m Database.HDBC Prelude Database.HDBC> :m + Database.HDBC.ODBC Prelude Database.HDBC Database.HDBC.ODBC> do { conn <- connectODBC "DSN=Nylon"; xs <- getTables conn; putStr $ head xs; } Loading package array-0.1.0.0 ... linking ... done. Loading package containers-0.1.0.1 ... linking ... done. Loading package bytestring-0.9.0.1 ... linking ... done. Loading package old-locale-1.0.0.0 ... linking ... done. Loading package old-time-1.0.0.0 ... linking ... done. Loading package mtl-1.1.0.0 ... linking ... done. Loading package HDBC-1.1.4 ... linking ... done. Loading package HDBC-odbc-1.1.4.3 ... linking ... done. CRASH !!! Thanks Morten

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happs install seems to have become very slow since upgrading cabal Re: [Haskell-cafe] test driving cabal install...
by Thomas Hartman 30 May '08

30 May '08

sudo cabal install --global HAppS-State went fine, and ghc-pkg had output on just the one (global) file. but sudo cabal install --global HAppS-Server is slooooooow. I finally canceled this and did sudo runghc Setup.hs build -v3 with the same result: extremely, extremely slow compile. It seems to get hung up one one line: src/HAppS/Server/Facebook.hs:416:2: Warning: Defined but not used: `a' *** Desugar: Result size = 52971 *** Simplify: Result size = 34350 Result size = 33980 Result size = 33972 Result size = 33972 *** Specialise: Result size = 52989 *** Float out (not lambdas, not constants): Result size = 55269 ... and more and more of same. for 15 minutes now. With verbose output on at least I can see there is something going on behind the scenes, but still. I don't remember things taking this long to compile before I upgraded to cabal v1.4... cabal bug? cabal --version cabal-install version 0.4.7 using version 1.3.11 of the Cabal library thomas. 2008/5/29 Thomas Hartman <tphyahoo(a)gmail.com>: > I see. I had done > > sudo cabal install HAppS-Server > > but this just installed with root ownership in my home directory. > > I'm now trying with > > sudo cabal install --global HAppS-Server > > > 2008/5/29 Daniel Patterson <daniel(a)dbpatterson.com>: >> I think you need to install HAppS-Data etc globally... I'm not sure why >> locally installed (ie, only your user) packages wouldn't be picked up by runghc >> Setup.hs'ing, but if they are install system wide it should definitely work. >> >> I think it is cabal --global install foo >> >> On Thu, 29 May 2008 18:11:04 -0700 >> "Thomas Hartman" <tphyahoo(a)gmail.com> wrote: >> >>> After a little drama with zlib, I managed to get cabal-install installed. >>> >>> I then attempted to do >>> >>> cabal install HAppS-Server >>> >>> since this is a module with a lot of dependencies, and in rapid >>> development flux, so perenially painful for me to install. >>> >>> The result is that I managed to install everything up to HAppS-State, >>> which I think is the last dependency, but then seemed to hang >>> indefinitely in the middle of installing HAppS-Server at the end. >>> >>> OK, I thought, then perhaps I can do normal runghc Setup.hs after >>> downloading and unzipping the tar from >>> >>> http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HAppS-Server-0.9… >>> >>> However, this resulted in error >>> >>> thartman@thartman-laptop:~/haskellInstalls/smallInstalls/HAppS-Server-0.9.2.1>runghc >>> Setup.hs configure >>> ... >>> Setup.hs: At least the following dependencies are missing: >>> HAppS-Data >=0.9.2... >>> >>> Strange, because I had just installed that module via cabal-install, >>> and I could load it in ghci with :m +HappS.Data. >>> >>> I then ran ghc-pkg and got this strange result that my packages were >>> broken into two different files. Is this by design? >>> >>> ghc-pkg list >>> /usr/local/lib/ghc-6.8.2/package.conf: >>> Cabal-1.2.3.0, Cabal-1.3.11, Cabal-1.5.2, DeepArrow-0.2, >>> .... >>> /home/thartman/.ghc/i386-linux-6.8.2/package.conf: >>> HAppS-Data-0.9.2.1, HAppS-IxSet-0.9.2.1, HAppS-State-0.9.2.1, >>> >>> >>> I am curious if anybody else is able to install HAppS-Server using >>> cabal install, and whether they can shed any light on the other isuses >>> I raised. >>> >>> Thomas. >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskell-Cafe(a)haskell.org >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >

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WebSense doesn't like darcs.haskell.org
by Chad Scherrer 30 May '08

30 May '08

My work uses WebSense to filter viewable pages - I don't have an option. I used to be able to get to darcs.haskell.org just fine, but apparently a /hacking directory was added somewhere, so WebSense put it on the naughty list. I put in a request for WebSense to review the site; hopefully it will soon be allowed again. But if not, I'll have to go through lots of red tape, which I'd really like to avoid. I assume/hope this "hacking" is only in the sense of making adjustments to code. Is this right? If there's anything involving DoS attacks, etc, I might never be able to get to it from work again. I get the impression WebSense is relatively widely used. Is anyone else here having similar trouble? Chad

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reordering pure bindings in monads
by Tim Newsham 30 May '08

30 May '08

Intuitively it seems like the applicative expression: (++) <$> getLine <*> getLine should represent the same thing as the more traditional liftM2 expressions: do { x <- getLine; y <- getLine; return ((++) x y) } but it seems to me that you cant directly manipulate the first into the second. I get: do x2' <- getLine x1 <- return ((++) x2') x2 <- getLine return (x1 x2) the only way I can get from here to the liftM2 definition is if I treat "x1 <- return ((++) x2')" as "let x1 = (++) x2", and then allow it to be reordered after the second getLine. Then it is straightforward to reduce to the liftM2 expression above. It seems to me that this is a valid transformation if: - no side effects, including pattern match errors, can occur in the let (or x1 <- return ...). - movement doesnt change the dependencies - x1 isnt used between the original line and its new position - there are no new bindings for x2' introduced between the original line and the new line. Did I overlook anything? Do any haskell implementations allow rewrites like these to occur? Tim Newsham http://www.thenewsh.com/~newsham/

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