- Haskell-Cafe - Haskell.org

Parsec question
by Ketil Malde 19 Apr '05

19 Apr '05

Hi, I've started using Parsec for my parsing needs, and must say I'm very happy with it. There is one thing that I'm struggling with implementing though. Basically, I want to parse a file containing multiple records. I already have a parser for a single record, and of course I could parse the file simply as many record However, this gives me the type Either ParseError [Record] which AFAICT, requires the whole file to be parsed correctly before any result is returned. I think it would be better for my purposes to have a parser of type [Either ParseError Record] so that the list of Records can be processed in an on-line fashion, until an error occurs. Is there an obvious way to achieve this? -kzm -- If I haven't seen further, it is by standing in the footprints of giants

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Re: Trying to implement this code
by Dmitry Vyal 18 Apr '05

18 Apr '05

Lizz Ross wrote: > > This gives me the error message :28 - Syntax error in input (unexpected > symbol "wrap") > Sorry. Looks like my mailer ate tabulation. Just correct the intendation: -- loads list of strings in the tree ins_list :: [String] -> BinTree Word_stat ins_list lst = foldl ins_in_tree Leaf (map wrap lst) where wrap :: String -> Word_stat wrap s = Word_stat s

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Re: [Haskell-cafe] Trying to implement this code
by Scott Turner 18 Apr '05

18 Apr '05

On 2005 April 18 Monday 13:42, Lizz Ross wrote: > Im trying to code a function to [...] create > a binary search tree containing the Strings and integers (where the > integers are the number of occurrences of each word. What have you got so far? Have you declared a data structure for the search tree? Have you seen http://haskell.org/hawiki/HomeworkHelp?

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HTTP and Browser modules
by Atwood, John Wesley 18 Apr '05

18 Apr '05

> 11. HTTP and Browser modules (David Owen) > Message: 11 > Date: Mon, 18 Apr 2005 02:28:17 +0000 > From: "David Owen" <d_w_o(a)hotmail.com> > Subject: [Haskell-cafe] HTTP and Browser modules > To: haskell-cafe(a)haskell.org > Message-ID: <BAY101-F23ED428D824D7DBAF21C54B3290(a)phx.gbl> > Content-Type: text/plain; format=flowed > > Good morning > > I have a query about compiling the original version of the HTTP > implementation in Windows > (http://homepages.paradise.net.nz/warrickg/haskell/http/) > <snip details> > If anybody has seen this problem before or knows how to > correct it I'd be very interested in your assistance :-) David, in HTTP.hs, replace the 2 occurences of "ioError" with "throw". John Atwood

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HTTP and Browser modules
by David Owen 18 Apr '05

18 Apr '05

Good morning I have a query about compiling the original version of the HTTP implementation in Windows (http://homepages.paradise.net.nz/warrickg/haskell/http/) Using the compile commands stipulated a series of similar errors to do with the HTTP module appear. They are to do with a type mismatch, one of these errors for example is: ./HTTP.hs:592: Couldn't match 'IOError' against 'Exception' Expected type: Exception -> IO (Either a [Char]) Inferred type: IOError -> IO (Either ConnError b) In the application 'handleSocketError sk' In the second argument of 'Control.Exception.catch', namely '(handleSocketError sk)' Line 592 is: readBlock sk n = (liftM Right $ fn n) `Exception.catch` (handleSocketError sk) Have hacked about for some time to no avail. I don't know why this occurs because the code appears exactly the same in the updated version (http://www.dtek.chalmers.se/~d00bring/haskell-xml-rpc/http.html) and that compiles, albeit in linux only due to the Cabal constraint. I need it to work in Windows though so must use the original version. (I need it to compile using GHC 6.2.2) If anybody has seen this problem before or knows how to correct it I'd be very interested in your assistance :-) cheers to all david

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Thompson's Exercise 9.13
by Kaoru Hosokawa 17 Apr '05

17 Apr '05

I've been working through Thompson's exercises and got to one I could not solve. It's Exercise 9.13. This is where I need to define init using foldr. init :: [a] -> [a] init "Greggery Peccary" ~> "Greggary Peccar" This is as far as I got: init xs = foldr left [] xs left :: a -> [a] -> [a] left x [] = [] left x1 : (x2 : xs) = x1 : (left x2 xs) But this returns [] and doesn't work. I can't get "left" to know that it is working with the rightmost element. It just throws away every element when its right hand side is empty. I found a solution that works for Strings, but I am looking for a more general solution. This exercise may yet again be one of those that is difficult to solve with my current knowledge of Haskell, but I'm asking anyway. -- Kaoru Hosokawa khosokawa(a)gmail.com

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GHC Survey source?
by Alson Kemp 15 Apr '05

15 Apr '05

Simons, Would y'all hand out the source code for the survey @ http://www.haskell.org/ghc/survey/start.cgi? I looked through the CVS repo but couldn't find it. Aside from generalities (GHC, WASH, etc), I wanted to see some actual web programming with Haskell. Thanks, Alson

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Do you use GHC?
by Simon Peyton-Jones 15 Apr '05

15 Apr '05

Dear Haskell folk, PLEASE READ THIS IF YOU USE THE Glasgow Haskell Compiler (GHC). I virtually never send messages to overlapping sets of lists, but I'm doing so this time, because I'd really like to get to everyone who uses GHC. Here at GHC HQ, we are often asked how many people use GHC, and what kind of folk they are. Since GHC is free software, we have no clue. Download stats tell us a bit, but not much, because GHC gets out through a variety of other routes too (e.g. Debian). We also have little idea about which aspects of GHC are most valued, nor of what enhancements would be most sought after, or which platforms are most important to you. We hear quite a bit from the bleeding-edge folk who push the limits, but much less from people who just want to get the job done. Thus motivated, Tomasz Zielonka kindly put together a (WASH-powered) survey for us, which asks you to tell us a bit yourself and how you use GHC. We've had about 230 responses so far; thank you to those 230 folk. But I'm pretty certain there are more than 230 people in the world who use GHC! THIS MESSAGE IS TO ASK YOU TO TAKE 5 MINS TO COMPLETE THE SURVEY http://www.haskell.org/ghc/survey/start.cgi We'd like to hear from *absolutely everyone* who uses GHC: whether you are a first-year undergraduate or a famous professor; whether you use GHC for industrial applications or recreation; whether you use higher-rank polymorphism or have only just learned what functional programming is. Everyone! We'll use the information to guide our future priorities, and we'll publish some kind of summary of what we learn in due course. It's all anonymous, of course, unless you choose to say who you are. If you think it's appropriate, please circulate this announcement locally, e.g. to your students who may not be on the Haskell mailing list Many thanks Simon PJ and Simon Marlow

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Haskell with Apache?
by Graham Klyne 14 Apr '05

14 Apr '05

I'm interested in running Haskell code invoked from an Apache web server request. I discovered the mod_haskell project [1] which looks prima facie v. promising. Does anyone have any recent experience of using this (there apparently being no recent activity on this project)? I wonder if there's any other project or activity in this area I should be aware of? #g -- [1] http://losser.st-lab.cs.uu.nl/mod_haskell/ ------------ Graham Klyne For email: http://www.ninebynine.org/#Contact

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Call for Contributions -- HC&A Report (May 2005 edition)
by Andres Loeh 14 Apr '05

14 Apr '05

Dear Haskellers, it is nearly time for the eighth edition of the ================================================================ Haskell Communities & Activities Report http://www.haskell.org/communities/ Submission deadline: 03 May 2005 (please send your contributions to hcar at haskell.org, in plain ASCII or LaTeX format) ================================================================ This is the short story: * If you are working on any project that is in some way related to Haskell, write a short entry and submit it to the me. * If you are interested any project related to Haskell that has not previously been mentioned in the HC&A Report, tell me, so that I can contact the project leaders and ask them to submit an entry. * Feel free to pass on this call for contributions to others that might be interested. More detailed information: The Haskell Communities & Activities Report is a bi-annual overview of the state of Haskell as well as Haskell-related projects over the last, and possibly the upcoming 6 months. If you have only recently been exposed to Haskell, it might be a good idea to browse the November 2004 edition -- you will find interesting topics described as well as several starting points and links that may provide answers to many questions. Contributions will be collected until the beginning of May. They will be compiled into a coherent report which will appear sometime during May. As always, this is a great opportunity to update your webpages, make new releases, announce of even start new projects, or to point at some developments you want every Haskeller to see! As the purpose of the report is to collect recent or current activities, we encourage you to update all existing summaries and reports. We will probably drop any topics that have not had any activity for the past year, i.e., since May 2004, but we would very much prefer you to present an updated description of the topic. Of course, new entries are more than welcome. Reports should generally be kept brief and informative, ranging from a few sentences to a few hundred words, to keep the whole report reasonably sized. Looking forward to your contributions, Andres (current editor) ----------------------------------- topics New suggestions for current hot topics, activities, projects, etc. are welcome - especially with names and addresses of potential contacts, but here is a non-exclusive list of likely topics (see also http://www.haskell.org/communities/topics.html ): General Haskell developments; Haskell implementations; Haskell extensions; Standardization and documentation; Haskell tutorials, howtos and wikis; Organisation of Haskell tool and library development; Haskell-related projects and publications; new research, fancy tools, long-awaited libraries, cool applications; Feedback from specialist mailing lists to the Haskell community as a whole; Haskell announcements; all (recent) things Haskell Announcements: if you've announced anything new on the Haskell list over the last six months, you'll want to make sure that is reflected in this edition! Project pings: if you're maintaining a Haskell tool or library or somesuch, you'll want to let everyone know that it is still alive and actively maintained, even if there have been no new additions, but all the more if there have been new developments. Tutorials: if you've fought with some previously undocumented corner of Haskell, and have been kind enough to write down how you did manage to build that graphical user interface, or if you've written a tutorial about some useful programming techniques, this is your opportunity to spread the word (short, topic-specific, and hands-on tutorials that only show how to achieve a certain practical task would do a lot to make things easier for new Haskellers - please write some!) Applications: if you've been working quietly, using Haskell for some interesting project or application (commercial or otherwise), you might want to let others know about what you're using Haskell for, and about your experiences using the existing tools and libraries; are you using Haskell on your job? An interesting thread about using Haskell and more generally functional programming for non-Haskell things seems to recur with reasonable frequency - why not write a sentence or two about your use of Haskell for our report? Feedback: if you're on one of the many specialist Haskell mailing lists, you'll want to report on whatever progress has been made there (GUI API discussions, library organisation, etc.) If you're unsure whether a contact for your area of work has come forward yet, have a look at the report's potential topics page, or get in touch with me. I have contacted last time's contributors, hoping they will volunteer to provide updates of their reports, and will update the contacts on the topics page fairly regularly. But where you don't yet see contacts listed for your own subject of interest, you are very welcome to volunteer, or to remind your local community/project team/mailing list/research group/etc. that they really ought to get their act together and let the Haskell community as a whole know about what they've been doing! :-) -------------------------- what should I write? That depends on your topic, but as a general rule, it shouldn't take you long. A simple sentence or two about your use of Haskell could go into the "Individual Haskellers and their projects" section. If you're a company, or if you're working on a project using Haskell as the implementation language, a paragraph on that could go into the "Commercial Applications" and "Non-Commercial Applications" sections. A typical summary report about a tool/library/project/application/... would be between 1 and 3 paragraphs of ASCII text (what's it about? major topics and results since the last report? current hot topics? major goals for the next six months?) plus pointers to material for further reading (typically to a home page, or to mailing list archives, specifications and drafts, implementations, meetings, minutes, ...). For those who prefer templates to fill in, the report is edited in LaTeX, and an entry template might look something like this: \begin{hcarentry}{<MYSTUFF>} \report{<MY NAME>} \status{<PROJECT STATUS IN ONE LINE>} \makeheader <WHAT IS IT?> <WHAT IS ITS STATUS? / WHAT HAS HAPPENED SINCE LAST TIME?> <CAN OTHERS GET IT?> <WHAT ARE THE IMMEDIATE PLANS?> \FurtherReading \url{<PROJECT URL>} \end{hcarentry} Browsing through previous editions should give you a good idea of the variety of possibilities, ranging from very brief to extensive.

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