Re: [Haskell-cafe] want to start a page of Haskell examples to go with Skiena's book The Algorithm Design Manual and also tie in Bird's equational reasoning for functional programming; ...
On Sun, 01 May 2011 03:23:03 +0200, cas...@istar.ca wrote: I want to start a page of Haskell examples to go with Skiena's book The Algorithm Design Manual and also tie in Bird's equational reasoning for functional programming; where is a good place for such examples. I think HaskellWiki is the best place for this, see for example: http://www.haskell.org/haskellwiki/99_questions/1_to_10 The page: http://www.haskell.org/haskellwiki/HaskellWiki:Contributing describes how to write wiki pages. Regards, Henk-Jan van Tuyl -- http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Binary and Serialize classes
On Fri, Apr 29, 2011 at 10:25 AM, Evan Laforge qdun...@gmail.com wrote:
Indeed, and I was starting to do that... well, I would make my own
project specific Serialize class, since the type dispatch is useful.
But copy pasting a UTF8 encoder, or the variable length Integer
encoder, or whatever seemed kinda unpleasant. Surely we could expose
that stuff in a library, whose explicit goal was that they *would*
remain compatible ways to serialize various basic types, and then just
reuse those functions? E.g. that is already done for words with the
putWordN{be,le} functions, and is available separately for UTF8.
I intend to add support for different UTF encodings to
Data.Binary.Builder for this very reason. I also intend to add two
functions to Data.Binary.Builder.Internal that lets you implement
variable length encoding as efficiently as possible.
I'm a bit skeptical of adding builders for different variable length
encodings to the library, simply because there are so many
possibilities. I think creating a binary-vle (for variable length
encoding) package would be worthwhile. I have an implementation of the
VLE used in protocol buffers.
Johan
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Re: [Haskell-cafe] Wai and http-enumerator not as lazy as I'd like
Michael Snoyman wrote: On Fri, Apr 29, 2011 at 2:49 AM, Erik de Castro Lopo Has anyone done anything like this and care to shed some light? It's a little bit complicated, but hopefully this should help out: Thats Michael. I've tried it and it works. Now to study it and figure out how :-) Cheers, Erik -- -- Erik de Castro Lopo http://www.mega-nerd.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [web-devel] Odd Ambiguous type variable `a0' in the constraint: error (with Yesod)
Without seeing the actual code that's causing the breakage, there's not much I can tell you. (If you'd like me to take a look off-list, feel free to send me a private email.) My best recommendation is to try putting a type signature on getRootR. As a general issue: polymorphic Hamlet is a very convenient feature, but I think it leads to too much complexity in the type system. I've added some code for non-polymorphic Hamlet to the Github repo and will be releasing it as its own module (Text.Hamlet.NonPoly) in the next release. Assuming all goes well, it will be replacing the current Hamlet. That essentially means that you'll need to replace your code with something like: getRootR = defaultLayout $ do setTitle Polymorphic Hamlet addHtml [$html|pI was added with addHtml|] addHamlet [$hamlet|pI was added with addHamlet|] addWidget [$whamlet|pI was added with addWidget|] And just to make everyone curious: I've also added i18n support to non-poly Hamlet. I've got a long train ride on Tuesday, and I'm planning on documenting it then. Michael On Sun, May 1, 2011 at 6:50 AM, Mathew de Detrich dete...@gmail.com wrote: Ok so I have a problem that was described here (http://permalink.gmane.org/gmane.comp.lang.haskell.web/1431) in regards to returning a Ambiguous type variable `a0' in the constraint error when compiling. Originally I thought it was due to the way I was coding that part of the code (or to be more accurate the code specifically for creating the so called widgets with addHTML/addWidget,addHamlet). So I copied the example code given here exactly (http://www.yesodweb.com/book/example-widgets). Compiling this worked fine, so at the next point I changed the definition of getRootR to getRootR = defaultLayout $ wrapper $ do setTitle Polymorphic Hamlet addHtml [$hamlet|pI was added with addHtml|] addHamlet [$hamlet|pI was added with addHamlet|] addWidget [$hamlet|pI was added with addWidget|] and then to getRootR = defaultLayout $ do setTitle Polymorphic Hamlet addHtml [$hamlet|pI was added with addHtml|] addHamlet [$hamlet|pI was added with addHamlet|] addWidget [$hamlet|pI was added with addWidget|] Both times compiled fine, so the issue wasn't what I originally thought that it was (as described in http://permalink.gmane.org/gmane.comp.lang.haskell.web/1431). The problem is, that when I use the above example code in my WebServer, I get this Ambigious type error when compiling (even though I have set up the route the exact same way). Unfortunatley I can't provide the code for my webserver, since its commercially owned (and it would be pointless because its just renamed variables, but otherwise its the same), so does anyone have any ideas what could possibly cause such an error (such as a missing/extra import or some package or something), or possibly some missing instances? Also sorry for creating another mailing list, but its a different issue then what I thought it was originally (and I also wanted to put it on haskell-cafe since its a more general issue) ___ web-devel mailing list web-de...@haskell.org http://www.haskell.org/mailman/listinfo/web-devel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Posix IO Unicode lookup exception
My guess is that you are closing the file descriptor out from under the handle. It is probably the handle that has the open iconv connection, and since it is never closed, you run out of memory. Why not just interact with the handle? Use hPutStr instead of fdWrite, and hClose instead of closeFd. - Mark ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] ANN: timeplot-0.3.0 - the analyst's swiss army knife for visualizing ad-hoc log files
Hello, Sorry for the broken link: the correct link to the presentation is: http://jkff.info/presentations/two-visualization-tools.pdf 2011/4/30 Eugene Kirpichov ekirpic...@gmail.com: Hello fellow haskellers, I announce the release of timeplot-0.3.0, the analyst's swiss army knife for visualizing ad-hoc log files. Links: * http://jkff.info/presentation/two-visualization-tools - a presentation saying what the tools are all about and giving plenty of graphical examples on cluster computing use cases. At the end of the presentation there's also a couple of slides about installation. It is a little bit outdated, it corresponds to versions just before 0.3.0. * http://hackage.haskell.org/package/timeplot * http://github.com/jkff/timeplot * The sibling tool, splot - for visualizing the activity of many concurrent processes - http://hackage.haskell.org/package/splot and http://github.com/jkff/splot . It has also gotten a couple of new features since my last announcement. The major new feature of tplot is the introduction of subplots, the 'within' plots. It allows one to plot data from several sub-tracks on one track of the graph: - several line- or dot-plots - several plots of sums or cumulative sums, perhaps stacked (to see how the sub-tracks contribute to the total sum - e.g. if your log speaks about different types of overhead and you wish to see how they contribute to the total) - stacked activity count plot - a generalization of the previous activity count plot, which allows you to, given a log saying like Machine started servicing job JOB1 ... Machine finished servicing job JOB1 etc, plot how many machines are servicing each job at any moment, in a stacked fashion - so, how loads by different jobs contribute to the whole cluster's load. The activity frequency plot plots the same on a relative scale. The syntax is, for example: within[.] dots or within[.] acount or even within[.] duration cumsum stacked etc. Note that these are of course just example use cases and the tool is universal, it is not in any sense specialized to clusters, jobs, overheads or actually even to logs. I'd like to encourage you to give it a try and look around for a use case :) If you do give the tool a try, please tell me if something goes wrong, be it an installation problem or a bug (the version is fresh released, so this is quite possible). -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/ -- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [ANN] mysql-simple - your go-to package for talking to MySQL
Hi, folks - Over the past few days, I've released two MySQL-related packages on Hackage that I think should be pretty useful. The first is mysql-simple: http://hackage.haskell.org/package/mysql-simple This is a mid-level binding to the MySQL client API. I aimed it squarely at being both fast and easy to use, and I'm very pleased with the results so far. - Performance: compared to HDBC-mysql, mysql-simple yields a 60% performance improvement on my real-world application. - Ease of use: compared again to HDBC, my real-world application's DB-specific code shrunk by 50% while achieving the above performance increase. - Type safety: it's intentionally hard to construct SQL queries by string concatenation, but of course I provide some nice safe APIs for formatting queries and converting results. That safety does not come at the expense of performance or expressive bloat, as the above results indicate. Because I know that some people favour interacting with their databases via a model such as iteratees, the mysql-simple library is built on top of a very lightweight library. That lower-level library is named mysql: http://hackage.haskell.org/package/mysql This is a low-level binding to the MySQL client API. It is aimed at high performance and simplicity, but more specifically for consumption by authors of higher-level database libraries. It is bare enough of features that it doesn't even perform conversion between Haskell and SQL types, but at the same time it uses bytestrings sensibly, cheaply avoids some nasty signal interruption problems with the MySQL client library, and abstracts some of the tiresome details of memory management. It gives a higher-level library complete control over result conversion, how to fetch results, and all that, so you can focus purely on building iteratees and not the lower-level gunk. Enjoy! B. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
