- Haskell-Cafe - Haskell.org

parse error on input `&'
by siso dagbovie 25 Apr '09

25 Apr '09

Hi, I've defined the following datatype with haskell data Graph a b = Empty | Context a b & Graph a b But I am having the error message: " parse error on input `&' ". I am wondering what it is wrong with my definition. How can I fix this? Thanks in advance. Kind regards

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Binary I/O options
by David Leimbach 25 Apr '09

25 Apr '09

I see that there are a few approaches to doing Binary I/O with Haskell, and the one I'm currently looking at using is Data.Binary from Hackage. I was just wondering what folks were choosing for building networked applications and doing Binary I/O. The approach I was about to take was to use Data.Binary to create ByteString for Network calls with a standard I/O package. Are there other good options? Dave

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leksah on window - problems with installation.
by Raja Koduru 25 Apr '09

25 Apr '09

Hello, I want to install leksah haskell IDE on my windows(xp) system. I download leksah's source (leksah-0.4.4.1). I also have gtk2hs (0.10.0) in my path. I am having ghc-6.10.2. As suggested on leksah's website.. I used "runhaskell setup configure" command But it is failing with this error "Configuring leksah-0.4.4.1... Setup: At least the following dependencies are missing: glib >=0.10, gtk >=0.10, gtksourceview2 >=0.10.0" I tried to do "cabal install glib" but not able to do so. Can you give me clues on how to go forward. with thanks & regards, raja koduru

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OT: Good Linux distro for netbook + Haskell?
by Magnus Therning 25 Apr '09

25 Apr '09

I've decided to shop around for other options when it comes to a Debian distro to put on my Eee PC 900. Since it has no HDD I want something that isn't too bloated (some is all right) and ideally leaves up to me what to install and what not to. At the same time I'd like to have up-to-date Haskell packages in the native packaging system available (sure, cabal-install is all right for the odd package, but I'd rather use the native packaging system). Debian Sid would be a contender, though (no offence, I know they work hard) it's often slow in providing the latest versions of packages. Arch Linux is very up-to-date, but I'm not convinced it's a distro suitable for an Eee without HDD (I'm prepared to be proven wrong though). Is there something else out there I should be looking at? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus identi.ca|twitter: magthe Haskell is an even 'redder' pill than Lisp or Scheme. -- PaulPotts

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ANN: Cute Hack - Hyena handler + Bamboo Blog Engine :)
by Jinjing Wang 25 Apr '09

25 Apr '09

Hia, A few interesting progress on Hack: * many middleware ported from Rack, including a lambda! ( just like a pony for wsgi, and a lobster for rack ) * 2 handlers, one for Kibro on fcgi / lighttpd, one for Hyena web server * apps are portable, Bamboo is a port of Panda that runs on Hack, works fine with both handlers * Hyena handler is still experimental A lambda app looks like this -- Main.hs source module Main where import Hack import Hack.Utils import Hack.Handler.Hyena import Hack.Contrib.Lambda main = run $ lambda dummy_app -- compile ghc --make -O2 Main.hs -- run ./Main now go to http://localhost:3000/lambda Cheers, Links: * [Hack] (http://github.com/nfjinjing/hack/tree/master) * [Bamboo] (http://github.com/nfjinjing/bamboo/tree/master) -- jinjing

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RE: [Haskell-cafe] Thread priority?
by John Van Enk 25 Apr '09

25 Apr '09

+1 Incredibly interested if this goes anywhere. Willing to help! -----Original Message----- From: Christopher Lane Hinson <lane(a)downstairspeople.org> Sent: Friday, April 24, 2009 10:48 PM To: haskell-cafe(a)haskell.org Subject: [Haskell-cafe] Thread priority? Is there any interest or movement in developing thread priority or any other realtime support in Haskell? Right now, if I have tasks that need to be responsive in real time, even if the realtime needs are very soft, it seems that the only option is to try to ensure that at least one hardware thread is kept clear of any other activity. To be very useful to me, thread priority would not need to come with very strict guarantees, but there would need to be a way to make sure that `par` sparks and DPH inherit the priority of the sparking thread. In part I ask because I'm working on a small library to support a degree of cooperative task prioritization. Friendly, --Lane _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe

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Haskell consultant wanted to develop small, Mac-based utility in Haskell or AppleScript
by R J 24 Apr '09

24 Apr '09

I need someone to code a short program for use on a Mac OS X (Leopard) that, in essence, takes as input a file containing a list of English words, and produces as output a file containing the words plus definitions, as extracted from any good dictionary. Though Haskell might not be the ideal language for this project, the utility is almost trivial, I'm a fan of Haskell, and would like to support the community. Those interested should email me at rj248842(a)hotmail.com. The specs are: 1. Takes as input a .txt file containing lines delimited by newline characters, with each line containing either no characters, an English word or phrase, or a comment (denoted by, for example, "--"). Thus, the input file might look like: -- Comment 1frustum bon mot -- Comment 2octagon rectangle 2. Produces as output a file (.txt, .rtf, or .docx format) containing the comments, the words or phrases (in bold), and their definitions, using either the dictionary (New Oxford American Dictionary, "NOAD") bundled with OS X or some credible online dictionary (such as merriam-webster.com) for words whose definitions aren't found in the NOAD. For example, given the above input file, the output file would be: -- Comment 1frustum |ˈfrəstəm| noun ( pl. -ta |-tə| or -tums ) Geometry the portion of a cone or pyramid that remains after its upper part has been cut off by a plane parallel to its base, or that is intercepted between two such planes. ORIGIN mid 17th cent.: from Latin, ‘piece cut off.’ bon mot |ˈbän ˈmō; ˌbô n ˈmō| noun ( pl. bons mots pronunc. same or |ˈmōz|) a witty remark. ORIGIN mid 18th cent.: French, literally ‘good word.’ -- Comment 2 octagon |ˈäktəˌgän; -gən| noun a plane figure with eight straight sides and eight angles. • an object or building with a plan or cross section of this shape. DERIVATIVES octagonal |äkˈtagənl| |ɑkˈtøgənl| |-ˈtag(ə)n(ə)l| adjective octagonally |äkˈtagənəlē| |ɑkˈtøgənəli| |ɑkˈtøgənli| |-ˈtag(ə)n(ə)li| adverbORIGIN late 16th cent.: via Latin from Greek octagōnos ‘eight-angled.’ rectangle |ˈrekˌta ng gəl|noun a plane figure with four straight sides and four right angles, esp. one with unequal adjacent sides, in contrast to a square. ORIGIN late 16th cent.: from medieval Latin rectangulum, from late Latin rectiangulum, based on Latin rectus ‘straight’ + angulus ‘an angle.’ I've attached a (zipped) AppleScript--it's just a few lines--and Automator workflow that work ok using Automator's "Get Definition of a Word" action. It took about fifteen minutes to write, but for some reason, that action doesn't extract the entire definition from the dictionary. If it would save time, you could work off of that code and deliver an AppleScript solution, or you could write Haskell code. _________________________________________________________________ Rediscover Hotmail®: Now available on your iPhone or BlackBerry http://windowslive.com/RediscoverHotmail?ocid=TXT_TAGLM_WL_HM_Rediscover_Mo…

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GHC 6.10.2 compatible problem.
by Andy Stewart 24 Apr '09

24 Apr '09

Hi, all! I saw GHC release new version now, and fix some bug. I want to know below pacakges whether works fine with GHC-6.10.2 before i upgrade it: cabal, gtk2hs, xmonad, yi, leksah Thanks! -- Andy

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Being impure within a 'pure' function
by Daniel K. 24 Apr '09

24 Apr '09

Hello, imagine the following situation: You want to implement e.g. Dijkstra's algorithm to find a shortest path between nodes u and v in a graph. This algorithm relies heavily on mutating arrays, so the type signature would look something like getDistance :: Graph -> Node -> Node -> IO Int Not mutating the underlying arrays would probably result in poor performance. BUT: For a constant graph, the distance between two nodes stays the same all the time, so in fact getDistance should be a pure function! So here is my question: Is there a way to write functions in Haskell that do some IO internally, but that are guaranteed to be side-effect free? Of course one would have to make sure that the array that is mutated inside getDistance must not be accessible from outside the function. Is that possible? If not, wouldn't that be desirable? If not, why not? Thanks Daniel

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ANNOUNCE: vacuum-cairo: a cairo frontend to vacuum for live Haskell data visualization
by Don Stewart 24 Apr '09

24 Apr '09

I am pleased to announce the release of vacuum-cairo, a Haskell library for interactive rendering and display of values on the GHC heap using Matt Morrow's vacuum library. This library takes vacuum's output, generates dot graph format from it, renders it to SVG with graphviz, and displays the resulting structure using the gtk2hs Cairo vector graphics bindings ... all at the GHCi command line. This tool is useful for examining Haskell data structures as they are represented directly in the heap. In particular, it makes sharing visible for the first time, as well as unboxed values. It should be useful for teaching Haskell, or for library authors debugging the design of their data structures. You can see pictures of the rendered display here: http://code.haskell.org/~dons/images/vacuum/intmap.png And youtube screencasts of vacuum-cairo in action: http://www.youtube.com/watch?v=oujaqo9GAmA Get it: cabal install vacuum-cairo And on Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/vacuum-cairo -- Don

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