August 2009 - Haskell-Cafe

Re: Any comments about Clojure language?
by Mark Volkmann 11 Aug '09

11 Aug '09

> On Mon, 10 Aug 2009 09:35:48 -0700, Don Stewart <dons at galois.com> > wrote: > > Another possible disadvantage of Clojure is the lack of high-quality > free online tutorials. I wrote an extensive intro. to Clojure at http://ociweb.com/mark/clojure/article.html. -- R. Mark Volkmann Object Computing, Inc.

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Re: Re[2]: [Haskell-cafe] unsafeDestructiveAssign?
by Job Vranish 11 Aug '09

11 Aug '09

Opps, didn't "reply to all" I hate it when that happens... On Tue, Aug 11, 2009 at 1:00 PM, Job Vranish <jvranish(a)gmail.com> wrote: > haha, yeah. > > What I'm actually trying to do is make a way to manipulate arbitrary > recursive algebraic data structures as if they were graphs (not for > performance reasons but because it makes manipulating them much easier) > > It's similar to the data-reify package, but I need it to work on any > algebraic datatype. > > I'm not planning on using it for actually production code. I'm mostly just > experimenting with as a potentially interesting language feature. > > - Job > > > On Tue, Aug 11, 2009 at 12:50 PM, Bulat Ziganshin < > bulat.ziganshin(a)gmail.com> wrote: > >> Hello Job, >> >> Tuesday, August 11, 2009, 8:45:29 PM, you wrote: >> > What I am trying to do is hyper unusual and I really do need an >> unsafeHorribleThings to do it. >> >> yes, assigning 5 to 8 is really unusual in math :) >> >> >> -- >> Best regards, >> Bulat mailto:Bulat.Ziganshin@gmail.com >> >> >

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Re: Examples
by John Lato 11 Aug '09

11 Aug '09

Hello, Looking at just examples, there are a few separate issues here. 1. Installation of example source for review 2. Building/installation of example programs For the second issue, the buildExamples flag suggested by Henning works well to actually build the examples with cabal, but the install location is still a problem. Most users wouldn't want example executables to go into their bin directory, especially not in the case of global installs. To the best of my knowledge, Cabal currently doesn't support separate installation locations for multiple executables, nor does it support building but not installing executables. With the first issue, the problem is simpler. There's no location for source code to be installed to. Users can download the package and unpack it themselves, or the developer can include demo source as a "data file" and install it to the datadir (IMO a poor choice). One option is to add support for different installation locations for each executable. Perhaps the --installdir flag could be extended to support a syntax like the following: --installdir=executableName:/path/to/install where if executableName matches one of the executables known to cabal, it will install just that executable to the specified location. This puts a larger burden on users, however, since they would need to know the name(s) of all the demo executables. It also doesn't address the issue of source location. Another way is to add a special type of executable for tests and demo programs to cabal. A user would specify a directory in the .cabal file (or command-line) to which tests would be installed. Cabal would then build the identified tests/demos for the package and put them into that specific directory, as well as the source code. This also answers the question of where to put executables that are Buildable but not Installable. Thoughts? Cheers, John Lato > Date: Sun, 9 Aug 2009 21:07:53 -0400 > From: "John D. Ramsdell" <ramsdell0(a)gmail.com> > Subject: Re: [Haskell-cafe] Examples > To: Haskell Cafe <haskell-cafe(a)haskell.org> > Message-ID: > <7687290b0908091807y1d4a5329w6b452c6a3af5e044(a)mail.gmail.com> > Content-Type: text/plain; charset=UTF-8 > > Maybe in addition to having a buildable boolean in a library or > executable section, there should be an installable boolean. It would > default to true, but when false, the library or executable section is > ignored during package installation. > > John >

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Haskell2Xml
by Dmitry Olshansky 11 Aug '09

11 Aug '09

Hello all, I need a convenient tool to generate Haskell types from XML W3C Schema Definition (xsd) and vice versa - generate instances for Haskell ADT's to make corresponding XML. It is just the same that HaXml do with DTD. I need - using XSD - support for unicode - using xml-attributes as far as elements are very desirable - by my opinion TemplateHaskell for generate instances is prefferable than using DrIFT (which used in HaXml) - both possibilities is great of course - generation of xsd by Haskell type is a good feature also and so on... Does this tool exist? Do some articles / thoughts / standards / recomendations about correspondence between XML and Haskell ADT's exist? Best wishes, Dmitry

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C2HS issues on Hackage
by Michael Snoyman 11 Aug '09

11 Aug '09

Hi all, I've written a Yaml library built on top of libyaml (the same C library at the core of Python's yaml library). All is well on my local system and my server; I'm currently using it in production. However, the build is failing on Hackage with the following build log: http://hackage.haskell.org/packages/archive/yaml/0.0.1/logs/failure/ghc-6.10 . It seems that whichever version of C2HS is installed on the server does not allow "type" (or perhaps other keywords?) to be used as C identifiers. Unfortunately, "type" is the name of a field in a C struct I need to integrate with. It's obviously not vital that I get it to compile on hackage, but 1) I'm worried this is a sign of a bigger problem, and 2) it's always nice to have the API documentation available online. Any suggestions? Thanks, Michael

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Any comments about Clojure language?
by Sukit Tretriluxana 11 Aug '09

11 Aug '09

Hi all, I start reading about Closure language (http://clojure.org) and it seems an interesting language. I don't know much about this language especially in comparison to Haskell feature by feature. Could it perhaps be what Haskell on JVM would have been with the dressing of Lisp syntax? Any one would like to chime in your comments about the language, in comparison to Haskell? Thanks, Ed

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Re: Announce: EnumMap-0.0.1
by Louis Wasserman 10 Aug '09

10 Aug '09

Pardon my asking, but are fromEnum and toEnum guaranteed to preserve order on types like Double? I'd like to see a Double-backed Patricia tree map, but are we certain that EnumMap as presented will behave properly on such types? Louis Wasserman wasserman.louis(a)gmail.com

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[ANNOUNCE] hgettext 0.1.10 - last major release
by Vasyl Pasternak 10 Aug '09

10 Aug '09

Hello, I've uploaded last (and latest) significant version on hgettext module. Currently it works fine, and has bindings to all gettext functions (from libintl.h). Next versions will be only bug fixes of this version. GNU GetText allows you only to create simple, standalone desktop applications for Linux, to make something complex you should use different trick, fortunately Haskell could do these tricks much easier than other languages (if you want to see, how to build Gtk application, which supports run time language switching, and shows information on two languages simultaneously you could download example from http://hgettext.googlecode.com/files/gtk-hello-0.0.2.tar.gz , or read about it from http://progandprog.blogspot.com/2009/04/multilingual-ui-and-dynamic-languag…) I don't see any strong reasons to write any combinators over this basic bindings. Haskell needs more powerful internationalization library, and I am plan to design it, but it will be completely different from gettext principles, so this library will be released with another name. CHANGELOG: * Added '--version' command line parameter to hgettext tool * Added support for literate haskell files to hgettext tool * Changed all functions to throw IOError when they fails instead of return Nothing * Added bindings for: ngettext, dgettext, dngettext, dcgettext and dcngettext functions -- Best regards, Vasyl Pasternak

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[Haskell Cafe] Parsec: using two different parser for the same string
by Paul Sujkov 10 Aug '09

10 Aug '09

Hi everybody, suppose I have two different parsers: one just reads the string, and another one parses some values from it. E.g.: parseIntList :: Parser [Integer] parseIntList = do char '(' res <- liftM (map read) (sepBy1 (many1 digit) (char ';')) char ')' return res parseIntString :: Parser String parseIntString = manyTill anyChar eof so for some input like this - "(1;2;3;4)" - I will have two different result: *Parlog> parseTest parseIntList "(1;2;3;4)" [1,2,3,4] *Parlog> parseTest parseIntString "(1;2;3;4)" "(1;2;3;4)" but the thing that I actually want is something like Parser ([Integer], String) - results from both parsers at a time, no matter whether one of them fails or not: *Parlog> parseTest parseIntListAndString "(1;2;3;4)" ([1,2,3,4], "(1;2;3;4)") it is impossible at first sight, because first parser to use will consume all the input, and there will be nothing to parse for the second one Parsec contains "choice" function, but it is implemented via <|> and that is mplus - so it tries second alternative only if the first one fails. Is it possible to use two parsers for the same string (with try-like backtracking, no input actually consumed till the second parser finishes)? I can assume only dirty hacks with the GenParser internals - manual position storing and backtracking - but that is obviously not good however, my first attempt to solve the problem was kind a like that: to parse string to String, and then to use it as an input for the next level parse call: parseIntListAndString :: Parser ([Integer], String) parseIntListAndString = do str <- parseIntString return (res str, str) where res str = case (parse parseIntList "" str) of Left err -> [] Right val -> val but the problems with such a method began when I switched from Parser to GenParser with user state: function parseIntList have to update the state, but it can't have the same state as the parseIntListAndString any more: it has it's own. I can explicitly pass the state from parseIntListAndString to parseIntList, but I see no suitable way for the parseIntList to update it. I can return the updated state value from the parseIntList function, and call setState on a result - but it seems rather ugly to mee. However, if nothing else will do, that is an alternative it is of course possible to use two different parsers sequentially, but it is also very ineffective: I need to use such multiple parsing on a relatively small substring of the actual input, so little backtracking would be a much nicier approach. Any suggestions? -- Regards, Paul Sujkov

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haskell embedded
by Kevin Smith 09 Aug '09

09 Aug '09

Hello, Could someone point me in the the direction of any references for using Haskell as an embedded language in an application. Xmonad seems to come to mind because the configuration files are written using Haskell. Any other information ? Thanks in advance.

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