- Haskell-Cafe - Haskell.org

Parsing arguments and reading configuration
by Magnus Therning 21 Sep '08

21 Sep '08

Hi all, I'm looking for some inspiration for an elegant solution to a silly little problem I have. This might have a general well-known solution, or maybe there's something particularly elegant possible in Haskell. I just thought I'd ask. When writing a command line tool I want to use a configuration file and then have the ability to override the configuration using command line arguments. When I've worked with command line arguments before I've used the trick of folding (>>=) over a list of functions that modify the "members" of a type, using the default values as the starting point. I like that, it's cute. First I thought I'd treat the configuration in a similar way, but then I noticed a slight ordering problem. The command line arguments should take priority over the contents of the configuration file, but the location of the configuration can be given as an argument. I could read the arguments twice, first to get the correct location of the config file, then load the config, and then read the arguments again to make sure they take priority. But that feels a little silly. Are there any more elegant solutions people are using? /M -- Magnus Therning (OpenPGP: 0xAB4DFBA4) magnus＠therning．org Jabber: magnus＠therning．org http://therning.org/magnus Haskell is an even 'redder' pill than Lisp or Scheme. -- PaulPotts

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broken link in documentation
by Manlio Perillo 21 Sep '08

21 Sep '08

Hi. Sorry if I use the mailing list for this, but in the documentation of Control.Monad.RWS (and the other Control.Monad.* modules), the link http://www.cse.ogi.edu/~mpj/ is broken. Manlio Perillo

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Updated formlets sample?
by Martin Huschenbett 21 Sep '08

21 Sep '08

Hi all, I found a blog post concerning formlets [1] in the web. Since looks very interesting I tried to compile the sample code with recent versions of HAppS and formlets from hackage. But this didn't work as the API of formlets has changed since this post. I tried to adopt the code to the new API but I was unable to finish this since there is a new monadic context I don't know to handle in the right way. So my question is, is there an updated version of this sample code in the web or has anybody tried to adopt it and can send me the results? Thanks in advance, Martin. [1] http://blog.tupil.com/formlets-in-haskell/

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Drawing an existing image into a cairo surface?
by Rafal Kolanski 21 Sep '08

21 Sep '08

Hi, I'm trying to, in addition to all the other things on my cairo surface, pull some images in from .png files. I've googled, I've looked in the docs, but there isn't any way I can see to load a .png file into a surface. The best I can find is withImageSurfaceFromPNG, but I can't make it work. The C guys can do: image = cairo_image_surface_create_from_png("blah.png"); and then: cairo_set_source_surface(cr, image, 10, 10); cairo_paint(cr) I tried playing around with unsafePerformIO but that just gets me into: /build/buildd/cairo-1.6.0/src/cairo-surface.c:382: cairo_surface_reference: Assertion `((*&(&surface->ref_count)->ref_count) > 0)' failed. Are any gtk2hs people around who can throw me in the right direction? Sincerely, Rafal Kolanski.

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The ultimate insult?
by Andrew Coppin 21 Sep '08

21 Sep '08

"Delphi is usable. If you're a single hobbiest programmer, use whatever gets the job done. But as far as a career goes, I'd say even Haskell has better prospects than Delphi." So "even Haskell" is better? Ouch! Still, in a bank-handed kind of way, I guess that means Haskell isn't as dead as Delphi yet, so it's also kind of a complement... of sorts...

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haskell shootout -- mandelbrot
by Tim Newsham 21 Sep '08

21 Sep '08

Since this one's trivially parallizable, I took a crack at the mandelbrot test case. It was fairly easy to thread it on a per-line basis in Haskell without changing the original too much. It might be more efficient to break the work into larger chunks, but that would require some slightly more complicated changes so I didn't try that yet. Anyway, the code and the results are here. See README for details: http://www.thenewsh.com/~newsham/shootout/ Tim Newsham http://www.thenewsh.com/~newsham/

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OpenSPARC project applicant chosen
by Duncan Coutts 21 Sep '08

21 Sep '08

I am very pleased to announce that we have chosen Ben Lippmeier for the OpenSPARC project. Congratulations Ben! Ben will spend three months hacking on GHC to make it perform well on the latest multi-core OpenSPARC chips. I would also like to thank the other people who applied. The reviewers were very impressed by the number of strong applications. About the project ----------------- http://haskell.org/opensparc/ It is a joint project between Sun Microsystems and the Haskell.org community. Sun has provided the funding for Ben to work on this full time for three months and has donated a powerful SPARC server for him and the rest of us to use. Ben will be working with Roman Leshchinskiy as a mentor and Darryl Gove as an adviser. Roman works on Data Parallel Haskell at UNSW and Darryl is a senior staff engineer in the SPARC compiler team at Sun. If you want to follow the progress we will be using the existing ghc development mailing list: http://www.haskell.org/mailman/listinfo/cvs-ghc and a corner of the ghc development wiki: http://hackage.haskell.org/trac/ghc/wiki/OpenSPARC Duncan (project coordinator)

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Hugs on the iphone
by Alberto R. Galdo 21 Sep '08

21 Sep '08

Hi, is there any chance of having hugs compile for the iPhone? Cross-compiling? Compiling directly on the iPhone? Greets, Alberto

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Iteratee-based IO
by oleg＠okmij.org 21 Sep '08

21 Sep '08

brian wrote: > I want to use Parsec to parse NNTP data coming to me from a handle I > get from connectTo. > One unworkable approach I tried is to get a lazy String from the > handle with hGetContents. It seems there is another approach, which is neither unsafe nor imperative. It relies neither on lazy IO nor on Handles. The input data can come from a file or from an embedded (e.g., chunk-encoded or encrypted) stream; the depth of embedding is arbitrary. The approach is naturally incremental. It permits IO interleaving without any unsafe operations. The approach is algebraic and declarative. The approach is the topic of the DEFUN08 talk in the morning of September 27. The code is already available http://okmij.org/ftp/Haskell/Iteratee/ The file http://okmij.org/ftp/Haskell/Iteratee/README.dr describes the other files in that directory. The running example is reading lines (terminated by CR, LF or CRLF) from a file descriptor and then from the chunk-encoded body. The main example illustrates multiplexing across two file descriptors and the full IO interleaving. The same line parser is used to process data from the file descriptor stream and from the embedded chunk-encoded stream, which is incrementally decoded. The whole code is Haskell98. It is not optimized at all and has no GHC-specific pragmas and options. The code has been used for the Wc program demonstrated yesterday. Perhaps the code answers the questions posed yesterday by Don. Hopefully one can see several composition modes for the iteratees and enumerators; enumerators are just iteratee transformers and compose as such. Incidentally, the operator ==<< is flipped >>==. Just like =<< (which is flipped >>=), it is like a `call-by-value application'. When a call-by-value language evaluates the application (f e), the argument e and all of its effects are executed first. Because of this analogy, I'm tempted to rename <<== into something like $. or .$ (or perhaps <$>, although the latter is taken).

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Configure bug? Re: SOLVED. Re: [Haskell-cafe] Linker Errors For OpenGL / GLUT 'Hello World' Program.
by Donnie Jones 21 Sep '08

21 Sep '08

Hello Brandon, Maybe this is a bug in the configure script of Haskell OpenGL or GLUT packages? Any suggestion from the package maintainers (or someone more familiar with these packages)? Thanks! :) __ Donnie On Sat, Sep 20, 2008 at 10:13 PM, Brandon S. Allbery KF8NH < allbery(a)ece.cmu.edu> wrote: > On 2008 Sep 20, at 22:10, Donnie Jones wrote: > > ghc -package GLUT -lglut Hello1.hs -o Hello1 --- works! :) > > I'm not sure why I must specify "-package GLUT" and "-lglut" but that > prevents the linker errors. Also, shouldn't configure correctly figure out > how to link the GLUT libraries? Can someone explain? > > > You're overriding the information recorded by ghc-pkg (which is used if you > use ghc --make). > > As for why configure doesn't work, I think you'd have to let someone who > knows the HOpenGL build stuff look at your system. > > -- > brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery(a)kf8nh.com > system administrator [openafs,heimdal,too many hats] allbery(a)ece.cmu.edu > electrical and computer engineering, carnegie mellon university KF8NH > > >

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