September 2008 - Haskell-Cafe

ANNOUNCE: citeproc-hs, a Haskell implementation of the Citation Style Language designed for Pandoc
by Andrea Rossato 22 Sep '08

22 Sep '08

Hello, I'm happy to announce the first release of citeproc-hs, a Haskell implementation of the Citation Style Language. citeproc-hs adds to Pandoc, the famous Haskell text processing tool, a Bibtex like citation and bibliographic formatting and generation facility. ABOUT The Citation Style Language (CSL) is an XML language for specifying citation and bibliographic formatting, similar in principle to BibTeX .bst files or the binary style files in commercial products like Endnote or Reference Manager. CSL is used by Zotero for bibliographic style formatting, and a huge number of CSL styles have been developed by the Zotero community. There are plans to use CSL in the future release of OpenOffice: http://bibliographic.openoffice.org/ citeproc-hs is a library that exports functions to parse CSL styles and MODS collections, to process lists of citation groups and to format the processed output. The output is a Haskell data type that can be further processed for conversion to any kind of formats (at the present time plain ASCII and the Pandoc native format) citeproc-hs was developed in order to add to Pandoc Bibtex like citations and automatic reference and bibliography generation. More information, with installation instructions, can be found here: http://code.haskell.org/citeproc-hs/ DOWNLOADS citeproc-hs can be downloaded from Hackage: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/citeproc-hs To get the darcs source run: darcs get http://code.haskell.org/citeproc-hs/ KNOWN ISSUES citeproc-hs is in an early stage of development and the CSL is not complete yet. Specifically, citation collapsing is not implemented, and some formatting options are not working neither. The MODS parser needs some refinement too. BUG REPORTS To submit bug reports you can you the Google code bug tracking system available at the following address: http://code.google.com/p/citeproc-hs/issues CREDITS Bruce D'Arcus, the author of CSL, has been very kind and patient with me when I was trying to understand the CSL schema, and provided me with ideas, comments and suggestions that made it possible to come to something usable. John MacFarlane, the author of Pandoc, has been very supportive of the project and provided a lot of useful feed back, comments and suggestions. Hope you'll enjoy, Andrea Rossato

2 2

Re: [Haskell-cafe] Line noise
by Richard A. O'Keefe 22 Sep '08

22 Sep '08

On 22 Sep 2008, at 9:19 am, Albert Y. C. Lai wrote: > Everyone should use exclusively ancient Egyptian iconography. It is > the only universally readable language. I know this was full of (:-) (:-), but it seems like the perfect chance to mention Blissymbols. http://unicode.org/roadmaps/smp/smp-4-14.html (the Unicode SMP road map) has a link to a proposal for adding them to Unicode, and they _are_ in active use... (A Haskell program in Blissymbols would be, well, bigger.)

1 0

Bird-style and blank lines
by Paulo Tanimoto 22 Sep '08

22 Sep '08

Hi, I'm a big fan of literate haskell, especially Bird-style, but there's one behavior that I find rather annoying: the requirement that code be preceded and followed by a blank line. Quoth the Report: "To capture some cases where one omits an ">" by mistake, it is an error for a program line to appear adjacent to a non-blank comment line, where a line is taken as blank if it consists only of whitespace." While that is something I do anyway, since it looks better, there are some cases where it would be nice to relax that. For example: 1. I see a blog post in literate style, but the author did not provide a .lhs file, sometimes copying and pasting the text will result in code being adjacent to the text. Then I have to fix that manually. 2. It would be nice for prototyping if you could quickly comment out code just by removing a ">" character, instead of inserting "--". 3. Pandoc, via markdown, is a very interesting alternative to latex. Right now you can write a block of code like this: ~~~ > fact :: Integer -> Integer > fact 0 = 1 > fact n = n * fact (n-1) ~~~ except that that won't work, precisely because you must have a blank line before and after the code. Unfortunately, when you go and add the blank lines, the output will show them. You may tell me to change what Pandoc does, but my point is that getting any markup to work with Bird-style will have this issue. The only argument I can see for keeping the requirement is what the report says, but feel free to provide others [1]. However, isn't that a bit like saying "we will require two semicolons because forgetting a semicolon is the number one source of mistake for our programmers"? Besides, I suspect most of us uses an editor with syntax highlighting (vi, emacs, yi, etc), and then it's immediately obvious you forgot something. Would it be hard to change this behavior in GHC? Is this open for discussion for Haskell Prime? Thanks, Paulo [1] I don't think it's that common to add a ">" by accident.

3 4

Language.Haskell and strings
by Maurício 22 Sep '08

22 Sep '08

Hi, I'm using Language.Haskell.* and would like to know if it's possible to pretty-print big strings like this: "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa" into something like this: "aaaaaaaa\ \aaaaaaaa\ \aaaaaaaa\ \aaaaaaaa\ \aaaaaaaa\ \aaaaaaaa\ \aaaaaaaa" to respect the limit on number of columns. Can you help me? Is it possible to do that? Thanks, Maurício

3 3

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

4 5

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

2 2

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/

2 2

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.

4 7

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...

2 1

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/

2 4