February 2011 - Haskell-Cafe

Rebindable 'let' for observable sharing?
by Henning Thielemann 01 Mar '11

01 Mar '11

Now that almost every syntax can be redirected to custom functions (RebindableSyntax, OverloadedStrings), would it make sense to map 'let' to 'fix' ? Would this open a way to implement observable sharing as needed in EDSLs by a custom 'fix'?

3 2

segfault when using ghc api
by Edward Amsden 28 Feb '11

28 Feb '11

I'm trying to run the following code. I'm not at all sure it's correct, it's based off of a bit of poking around in the ghc api. Running it with a command line argument like "show (5 + 2)" gives me a segmentation fault. Poking around with gdb and following the steps at http://hackage.haskell.org/trac/ghc/wiki/Debugging/CompiledCode yields precisely nothing, as even the "disassemble" command complains "No function contains program counter for selected frame." Any ideas? == code == module Main where import GHC import DynFlags import Data.Dynamic import System evalString :: Typeable a => String -> IO (Maybe a) evalString s = defaultErrorHandler defaultDynFlags $ runGhc Nothing $ do dynflags <- getSessionDynFlags setSessionDynFlags $ dynflags target <- guessTarget "Prelude" Nothing setTargets [target] load LoadAllTargets dyn <- dynCompileExpr s return $ fromDynamic dyn main = do (s:_) <- getArgs e <- evalString s putStrLn $ maybe "oops" id e -- Edward Amsden Undergraduate Computer Science Rochester Institute of Technology www.edwardamsden.com

3 4

HANSEI in Haskell?
by Daryoush Mehrtash 28 Feb '11

28 Feb '11

Is the "Embedded domain-specific language HANSEI for probabilistic models and (nested) inference" described in: http://okmij.org/ftp/kakuritu/index.html#implementation available in Haskell? Is there a reason why the author did the package in Ocaml rather than Haskell? -- Daryoush

3 8

HDBC's future and request for help
by John Goerzen 28 Feb '11

28 Feb '11

Hi folks, HDBC has been out there for quite some time now. I wrote it initially to meet some specific needs, and from that perspective, it has been done for awhile. It is clear, however, that there are some needs it doesn't meet. Most of them relate to specific backend driver items. I'd like to start some discussion in the community about what the future of HDBC and its backend drivers ought to look like. Some models might be: 1. I continue as maintainer for HDBC and HDBC-{postgresql,odbc,sqlite3} and act as patch manager/gatekeeper for patches that are discussed on some public mailing list. 2. Interested parties adopt the backend drivers while I continue to act as maintainer/patch manager/gatekeeper for HDBC itself. 3. Interested parties adopt all of HDBC and maintain it I am not expressing a particular preference for any of these options; just putting them forth. Here are some of the current issues I am aware of: 1. I have no Windows development platform. I can't test the releases on Windows. Many Windows users don't have the skill to diagnose problems. These problems do eventually get fixed when a Windows user with that skill comes along -- and I appreciate their efforts very much! -- but it takes longer than it ought to. 2. The ODBC documentation is monumentally terrible, and the API is perhaps only majestically terrible, and it is not 100% clear to me all the time that I have it right. A seasoned ODBC person would be ideal here. 3. Issues exist with transferring binary data and BLOBs to/from at least PostgreSQL databases and perhaps others. There appear to be bugs in the backend for this, but BLOB support in the API may need to be developed as well. 4. Although the API supports optimizations for inserting many rows at once and precompiled queries, most backends to not yet take advantage of these optimization. 5. I have received dueling patches for whether foreign imports should be marked "safe" or "unsafe" on various backends. There seems to be disagreement in the community about this one. 6. Many interactions with database backends take place using a String when a more native type could be used for efficiency. This project may be rather complex given varying types of column data in a database -- what it expects for bound parameters and what it returns. The API support is there for it though. 7. Various other more minor items. Thoughts? -- John

4 11

Re: [Haskell-cafe] ANN: theoremquest-0.0.0
by Tom Hawkins 28 Feb '11

28 Feb '11

> I find this fairly interesting. Once you're finished grappling with the > logical core, I wouldn't mind helping out with a web interface, time > permitting. I suspect attracting mass appeal, or getting users at all, is > helped massively by having a web interface. Thanks for your interest. Yes, a web interface would be ideal. Currently the library has hooks to translate the transactions to JSON to ease construction of any Javascript client -- thought these translations still need to be implemented. Note the 'RspInJSON' request: http://hackage.haskell.org/packages/archive/theoremquest/0.0.0/doc/html/The…

1 0

trac.haskell.org problem
by Niklas Broberg 28 Feb '11

28 Feb '11

Ah, I suppose that's to do with the trac server itself, that's beyond me. Moving to café: Does anyone know what's up with trac.haskell.org not sending out verification emails? Cheers, /Niklas ________________________________________ From: Jurriaan Hage [jur(a)cs.uu.nl] Sent: Monday, February 28, 2011 8:41 AM To: Niklas Broberg Subject: Re: Again a question about haskell-src-exts. On Feb 28, 2011, at 8:39 AM, Niklas Broberg wrote: > I suppose I do - to the extend I can. What's the issue? :-) The system does not send out verification e-mails, so I can not really register completely and submit new issues. I have tried it with two different e-mail accounts, and somebody else has tried too. They also do not show up in spam folders. Jur

2 1

ANN: Hakyll 3
by Jasper Van der Jeugt 28 Feb '11

28 Feb '11

Hello all, I've just uploaded the 3.0.0.0 version of Hakyll [1] to Hackage [2]. This is a complete rewrite, and completely backward-incompatible with previous versions. Sorry for that. On the other hand, I believe almost all aspects of the library have improved tremendously. Hakyll now uses a declarative EDSL in Haskell to specify compilation rules, and an arrow-based EDSL to describe the compilation process. If you want to have a quick look, I recommend have a glance at the example in the tutorial [3]. More documentation needs to be written, but I wanted to make sure I can incorporate your feedback into that process. [1]: http://jaspervdj.be/hakyll/ [2]: http://hackage.haskell.org/package/hakyll-3.0.0.2 [3]: http://jaspervdj.be/hakyll/tutorial.html Cheers, Jasper

1 0

http://www.cs.cornell.edu/icfp/task.htm
by Hauschild, Klaus (EXT) 28 Feb '11

28 Feb '11

Hi, Currently I'm trying to lern Haskell by doing. After doing some examples I plan to solve an ICFP task (see subject). In short: build an interpreter for a stack based language thata describes a 3D scene. Ray trace this scene in an image. My current source state can be found here: http://code.google.com/p/hgmltracer/source/browse/ My first goal is to develop the interpreter of the GML language. My source contains a data GmlToken with various constructors for the different operators, sequences, int, real, string an so on. Some code for the evaluation is also there und working. But the parser converting a string (contained in the program file provided as command line argument) is hard stuff and I'm stuck. Can any one help me with ideas or concepts for this parser? Thanks

3 4

Re: [Haskell-cafe] [SOLVED] why is ghci trying to load hsc file ??
by briand＠aracnet.com 28 Feb '11

28 Feb '11

On Mon, 28 Feb 2011 02:58:58 +0000 Felipe Almeida Lessa <felipe.lessa(a)gmail.com> wrote: > On Sun, Feb 27, 2011 at 6:48 AM, by way of briand(a)aracnet.com > <briand(a)aracnet.com> wrote: > > the binding-DSL examples do NOT use the above PRAGMA anywhere in the > > code. > > Probably they have > > Extensions: ForeignFunctionInterface > > on their .cabal file. > as I do, hence the reason for my confusion :-( Something's not working right and I can't begin to guess why not. I had to put the actual pragma in my .hsc file to make things work, and now it works. Brian

1 0

Render fonts in HopenGL
by er9999 27 Feb '11

27 Feb '11

Hello, Can anyone give me an example for fonts rendering? I tried to use FTGL library, but it is too complicated on Windows(compile). Is it possible to do it in a simple way? I need more than the given example in red book(Font.hs), something like outline font. By the way, I am new in OpenGL and Haskell, so the real exmaple should be the best. Thanks!

2 1