November 2008 - web-devel

Lazy simpleHTTP
by Henning Thielemann 14 Dec '08

14 Dec '08

I have HTTP-3001.0.4 and I like to check the HTTP response headers before downloading the entire document. I hesitate to do a HEAD request first and then a separate GET request, because there is a (little, but not zero) chance, that the document changes between both requests. I hoped that simpleHTTP is lazy enough, so that I can check the rspHeaders field of the HTTP response and that only touching rspBody would download the document content. Unfortunately simpleHTTP downloads the entire document before I can access the HTTP header. To be honest, I would also like to fetch the content of the document lazily. Actually, if simpleHTTP would behave lazy, I suspect this requires using unsafeInterleaveIO internally, which is considered a hack. Is this the reason why simpleHTTP is not lazy? Or do I just need a lazy Stream type for this purpose?

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HaskellWiki: Category:Web
by Henning Thielemann 28 Nov '08

28 Nov '08

I wondered why there was still no category for web applications on the Haskell Wiki, so I have initialized one: http://www.haskell.org/haskellwiki/Category:Web

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Where do you start?
by Artyom Shalkhakov 24 Nov '08

24 Nov '08

Hello, I'd like to share some links, gathered with much help from other mailing list subscribers. There seem to be plenty of ways to get the job done for a Haskell web developer, aside from using more common languages. :) First, the do-it-yourself way. There are CGI/FCGI [1], [2] bindings, so you can use your binaries with almost any webserver. A very nice templating engine [3] is also available. If you wish to embed (X)HTML in Haskell, you can use either the combinator libraries [4], [5] or [6] (which is highly experimental). Low-level libraries like [7],[8] can be used for database connectivity, while [9] is for those who would like to construct their queries using combinators. You can also take a look at lightweight frameworks like [10], [11]. Finally, in the near future we'll hopefully have a very robust and high-performance HTTP web-server [12] which is going to be very simple to start with. And about the frameworks out there. There are a few all-in-one frameworks ([13], [14]) available for those who can dive into the code, because their documentation is quite lacking. (Of course, you can help out the authors by proposing some!) If you're interested in HAppS, there is a tutorial to help you [15], and you can take [16] as a reference. I'm very grateful to all the people who responded to my inquiry! Regards, Artyom. [1] CGI, <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/cgi> [2] FCGI, <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/fastcgi> [3] HStringTemplate, <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/HStringTemplate> [4] Text.Html, a combinator library <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/html> [5] Text.Xhtml, a combinator library <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/xhtml> [6] VXML <git://mawercer.de/vxml> [7] Takusen <http://darcs.haskell.org/takusen/> [8] HDBC <http://software.complete.org/software/projects/show/hdbc> [9] HaskellDB <http://haskelldb.sourceforge.net/> [10] HVAC (Haskell View and Controller) <http://community.haskell.org/~sclv/hvac/> [11] Kibro <http://hackage.haskell.org/cgi-bin/hackage-scripts/package/kibro> [12] Hyena: <http://github.com/tibbe/hyena/tree/master>, <http://www.galois.com/blog/2008/09/12/left-fold-enumerators-a-safe-expressi…> [13] HAppS, the Haskell Application Server <http://happs.com/> [14] Turbinado, an early stab at Ruby On Rails <http://turbinado.org/> [15] Real World HAppS: The Cabalized, self-demoing HAppS Tutorial <http://happstutorial.com/> [16] Gitit, a wiki written using HAppS and git <http://github.com/jgm/gitit/tree/master/>

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Where do you start?
by Артем Шалхаков 20 Nov '08

20 Nov '08

Hello, I'm interested in Haskell web programming. Quick googling took me to HAppS, HVAC, WASH and do-it-yourself blog posts. I tried HVAC, which doesn't build on GHC 6.10.1 (if somebody's interested, I'll post some compiler complaints). I really like its approach, though. Then I tried to DIY: wired Haskell to Lighty using FastCGI. This approach works, but leaves very much to desire: XHTML combinators don't really give you compile-time validation, so what is the point of writing it in code? I had thought I'd need some templating, so I tried HStringTemplate to find that it doesn't build on my GHC (BTW, this templating engine has some neat concepts, which I like :-)). Then I turned to HAppS, which is painfully slow to build on my development machine, and I think it is too monolithic. Besides, it looks like it depends on mostly experimental GHC features, and lacks documentation! I'm not a Haskell Jedi, so I think there's no way I can make it to work. I found out that WASH uses CGI, which is sooo retro. Is it just my misunderstanding, maybe? There's also a question regarding which DBC library to use. Hackage has Takusen, HaskellDB, HDBC, HSQL. So which one? I'd be very glad if somebody gave an advice to a noob Haskell web programmer. :) Regards, Artyom.

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Ocaml has an ocaml virtual machine in JS now
by Marc Weber 18 Nov '08

18 Nov '08

:-) We already have a haskell to javascript compiler.. It's not an interpreter though.. ----- Forwarded message from Vincent Balat <vincent.balat(a)pps.jussieu.fr> ----- m: 0 (Mail was not recognized as spam) X-GMX-UID: Y5UUIa4CZDI5lllf82Y2BshxemhmYwEo Status: O Content-Length: 1017 Lines: 27 [Mail from Benjamin Canou redirected to the list] Hi, O'Browser is an implementation of the OCaml virtual machine in JavaScript, designed to run in web browsers. It features a runtime library compatible with OCaml's standard one (including OOP and concurrent threads) and bindings of some JavaScript functions to manipulate the DOM primitives. The distribution is available at [1] and an online version of the tutorial is reachable at [2]. Please note that this is an early version, in particular the DOM interface module is neither pretty nor well typed. However, it can already be used to create little applets or scripts (as in the tutorial [2], the examples of the distribution [3] or my webpage [4]) and we'll be glad to receive your comments or bug reports. Have fun. Benjamin Canou. [1] http://www.pps.jussieu.fr/~canou/obrowser-0.1.tar.bz2 [2] http://www.pps.jussieu.f ----- End forwarded message -----

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The Real Monad Transformer or is Haskell.org hijacked?
by Henning Thielemann 13 Nov '08

13 Nov '08

On Tue, 3 Apr 2007, Henning Thielemann wrote: > It was argued that people avoid Haskell because of terms from Category > theory like 'Monad'. This problem can now be solved by a wrapper which > presents all the WWW without monads! Start e.g. at > http://saxophone.jpberlin.de/MonadTransformer?source=http%3A%2F%2Fwww%2Ehas… > Of course the tool is written in Haskell, that is, Haskell helps solving > problems which only exist because of Haskell. > Bug reports and feature requests can be tracked at > https://sourceforge.net/projects/parallelweb The produced content has not changed very much, but the interface is much more friendly now. You can now enter the world of the Real Monad Transformer e.g. at: http://www.haskell.org.monadtransformer.parallelnetz.de/haskellwiki/Categor… Good luck! Henning

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