April 2009 - Haskell-Cafe

Takusen, postgres and boolean fields
by Sasha Shipka 25 Apr '09

25 Apr '09

Let say one has to do something similar to this: execDML $ cmdbind (sql "update some_table set some_boolean_field = ? where ...") [bindP True, ...] When I do it, I have an error: DBError ("42","804") 7 "ERROR: 42804: column \"some_boolean_field\" is of type boolean but expression is of type text ..." I've noticed that when I read boolean fields from postgres it reads them as string "t" or "f". So I also tried bindP "t" and had same error.

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Not in scope
by siso dagbovie 25 Apr '09

25 Apr '09

Hi, I've defined the datatype: data Graph a b = Empty | Context a b :& Graph a b and the function isEmpty :: Graph a b -> Bool isEmpty Empty = True isEmpty _ = False and when I do a test run with the graph, ( [ ],2,'c',[("down",3)]) :& Empty Haskell is bringing the message " Not in scope: data constructor `:&' " Why is that so? Kind regards

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compilation to C, not via-C
by Sam Martin 25 Apr '09

25 Apr '09

Hi Everyone, It appears the GHC compiler (and other) compile Haskell *via-C* but not *to C*. I've never really understood why there isn't a C generation option, or why GDC ships with its own compulsory copy of gcc. I work in Games middleware, and am very interested in looking at how Haskell could help us. We basically sell C++ libraries. I would like to be able to write some areas of our libraries in Haskell, compile the Haskell to C and incorporate that code into a C++ library. As an example, I think Haskell would be great at doing geometry processing. I don't want to write all our geometry processing code in C++. I'd prefer to write a big chunk of it in Haskell and wrap that in C++. The pattern here is using Haskell to generate C code as the end result. It sounds like this end result isn't that far out of reach, so I'm curious as to why it doesn't appear to be possible at present. Have I missed something? Is there some fundamental reason this isn't possible? Has anyone wished for this before? Any thoughts/help much appreciated, Thanks, Sam Martin --- Lead Programmer www.geomerics.com

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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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