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Trying On Learn Haskell Web Server
by Aditya Siram 03 Mar '06

03 Mar '06

Hi all, I am former imperative programmer (Java/C/Python) I have recently discovered Haskell and read through "Yet Another Haskell Tutorial" (the best I have found) and "Tackling The Awkward Squad". This paper mentions a Haskell Web Server (HWS) but I am not able to find the source. Where can I find the source? Has this code been updated since the paper was written? Can it be compiled and run on a recent version of GHC?Hugs? I would like to use it as an example program to teach myself Haskell. Thanks... Deech

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Trying On Learn Haskell Web Server
by Aditya Siram 03 Mar '06

03 Mar '06

Hi all, I am former imperative programmer (Java/C/Python) I have recently discovered Haskell and read through "Yet Another Haskell Tutorial" (the best I have found) and "Tackling The Awkward Squad". This paper mentions a Haskell Web Server (HWS) but I am not able to find the source. Where can I find the source? Has this code been updated since the paper was written? Can it be compiled and run on a recent version of GHC?Hugs? I would like to use it as an example program to teach myself Haskell. Thanks... Deech

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translating Haskell into theorem provers
by Gerwin Klein 01 Mar '06

01 Mar '06

Hi, is any of you aware of activities that aim to translate Haskell into interactive theorem provers like PVS or Isabelle/HOL? (automatically or manually). We know about the Programatica project and Brian Huffman's work, but turned up little else. Cheers, Gerwin

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Visual Haskell: Could not find module `Control.Monad.Writer'
by Bernd Holzmüller 01 Mar '06

01 Mar '06

Hi all, I am playing around with Visual Haskell, V0.1 (which really is great stuff!). In the main module I wrote the following import: import Control.Monad.Writer for which I get the error message: Could not find module `Control.Monad.Writer': use -v to see a list of the files searched for I use the GHCOptions: -fglasgow-exts -fallow-overlapping-instances. Is this a bug in Visual Haskell or what's wrong here? Thanks, Bernd

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-fno-monomorphism-restriction makes type-inference ambiguous?
by Eike Scholz 27 Feb '06

27 Feb '06

Hi, thanks for the last help and hints. I have encountered an other problem, and again I don't quite understand the reason why I get the results I get. ghci seems to infer different types for the same expression. Consider that I have disabled the monomorphism restriction in module AGC.lhs (which is attached). and I have a toplevel definition of: > mylength = synAttr listLength loding the module in ghci (6.4) gives (beside some correct warnings): $ Ok, modules loaded: Main. $ *Main> :type synAttr $ synAttr :: (Data b) => ((?stack::[Dyn]) => b -> a) -> Attr a $ *Main> :type listLength $ listLength :: (?stack::[Dyn]) => List -> Float $ *Main> :type (synAttr listLength) $ (synAttr listLength) :: Attr Float $ *Main> :type mylength $ mylength :: (?stack::[Dyn]) => Dyn -> Dyn -> [Dyn] -> Maybe Float $ *Main> let mylength = synAttr listLength $ *Main> :type mylength $ mylength :: Dyn -> Dyn -> [Dyn] -> Maybe Float where > type Attr a = Dyn -> Dyn -> [Dyn]-> Maybe a the problem I have is that inferred types for the toplevel declaration mylength differ from the verbatim equal definition in the Let experssion. for the toplevel it infers: mylength :: (?stack::[Dyn]) => Dyn -> Dyn -> [Dyn] -> Maybe Float for the let-Binding mylength :: Dyn -> Dyn -> [Dyn] -> Maybe Float and this is what I expected. Has anyone an Idea, why this happens? best regards, Eike Scholz PS: Beware of the comments in the attached file. This file is under heavy development. I am dyslexic and don't correct the comments while continuously rewriting code and comments. I hope that the comments are useful anyway. The (+>) (~>) (#>) operators are broken at the moment and don't work the way intended.

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RE: [Haskell] "strange" behavior of Implicit Parameters
by Simon Peyton-Jones 27 Feb '06

27 Feb '06

Look at the type of (???) (???) :: a -> (a->b) -> b Nothing about ?foo in there. You're passing a *monomorphic* function to (???), so fun is partially applied to ?foo before calling (???). Simon | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Eike Scholz | Sent: 27 February 2006 00:14 | To: haskell(a)haskell.org | Subject: [Haskell] "strange" behavior of Implicit Parameters | | Hi, | | I have just a short question, about the semantics of Implicit parameters | on GHC 6.4. | | Given the following code: | | > (???) x f | > = let ?foo = 1337 | > in f x | | > fun :: (?foo::Int,Show x) => x -> String | > fun x = "x = "++(show x)++"; ?foo = "++(show ?foo) | | > test = let ?foo = 23 | > in 42 ??? fun | | I would expect: | | test == "x = 42; ?foo = 1337" | | Because I thought, that it gets reduced like: | | let ?foo = 23 in 42 ??? fun | ~> let ?foo = 23 in (let ?foo = 1337 in fun 42) | ~> ... | ~> "x = 42; ?foo = 1337" | | however I get | | "x = 42; ?foo = 23" | | in ghci. | | Is there a special reason, why the implicit parameter is reduced first? | Could it be a bug? | | Reducing it my way would be very useful for combinator-libraries, since | it could be used passing around state info, or simple debug text, that | tells where a Runtime-error occured? | | an odd example: | | | > undef = error ?errstr | | > (<?>) x s = let ?errstr = ?errstr++"\n"++s in x -- annotate error tags | | | so error annotations will accumulate and it would be easy to resolve | runtime errors. | | | best regards | | Eike Scholz | | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

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Haskell Weekly News: February 27, 2006
by dons＠cse.unsw.edu.au 26 Feb '06

26 Feb '06

Haskell Weekly News: February 27, 2006 Greetings, and thanks for reading issue 26 of HWN, a weekly newsletter covering developments in the Haskell community. Each Monday, new editions are posted to [1]the Haskell mailing list and to [2]The Haskell Sequence. [3]RSS is also available. 1. http://www.haskell.org/mailman/listinfo/haskell 2. http://sequence.complete.org/ 3. http://sequence.complete.org/node/feed A fairly quiet week this week. Announcements * Long Live Edison. Robert Dockins [4]announced he had revived the Edison data structure code, and is maintaining a darcs repository, with a view to modernising the codebase. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/13295 Haskell' This section covers activity on [5]Haskell' this week. * [6]The hierarchical module system * [7]Refactoring the array interface * [8]The worst syntax in Haskell * [9]Module export lists * Public/private sections [10]part 1 and [11]part 2 5. http://hackage.haskell.org/trac/haskell-prime 6. http://article.gmane.org/gmane.comp.lang.haskell.prime/619 7. http://article.gmane.org/gmane.comp.lang.haskell.prime/629 8. http://article.gmane.org/gmane.comp.lang.haskell.prime/632 9. http://article.gmane.org/gmane.comp.lang.haskell.prime/721 10. http://article.gmane.org/gmane.comp.lang.haskell.prime/741 11. http://article.gmane.org/gmane.comp.lang.haskell.prime/754 Darcs Corner * darcsweb 0.15-rc1. Alberto Bertogli [12]announced that a new version of darcsweb is available. 12. http://article.gmane.org/gmane.comp.version-control.darcs.user/9535 Contributing to HWN You can help us create new editions of this newsletter. Please see the [13]contributing information, send stories to dons -at- cse.unsw.edu.au. The darcs repository is available at: darcs get http://www.cse.unsw.edu.au/~dons/code/hwn 13. http://haskell.org/haskellwiki/HWN

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how to write an interactive program ? gui library to use ?
by minh thu 25 Feb '06

25 Feb '06

Hi all, 1/ I'd like to know how can I implement an interactive program (an editor) in haskell where some "things" have to be updated. The "things" can be text in a word processor, or a pixel array in a 2d graphics editor, and so on. Have I to pass the state (the "things") explicitely in the arguments of the main loop (a recursive function) ? Sorry if it's stupid... 2/ Another one concerning gui library: what's the best choice ? I need it to work both on linux and windows. I also need it can handle an OpenGL context. thanks a lot, minh thu

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CFP: Mathematically Structured Functional Programming
by Conor McBride 23 Feb '06

23 Feb '06

CALL FOR PAPERS Workshop on Mathematically Structured Functional Programming MSFP 2006 Kuressaare, Estonia, 2 July 2006 http://cs.ioc.ee/mpc-amast06/msfp/ a satellite workshop of MPC 2006 a "small workshop" of the TYPES project Background Something wonderful happened when monads arrived in Haskell: some human mathematics explaining the structure of certain computational phenomena became a mechanical means to implement those phenomena. It's a good way to go about functional programming - to dig out the mathematical structure underlying a problem and set it to work! There's more where monads came from, and we want it. This new workshop is about getting it. In recent years, a diverse array of mathematical structures has appeared in our programs: monads dualise to comonads and generalise to Freyd categories aka 'arrows'; 'container' types have a generalised polynomial structure supporting generic programming, not to mention a differential calculus; isomorphisms from 'high school algebra' are used to search libraries and repair type errors; coalgebras give structure to recursion; the list goes on... MSFP is broad in scope, covering the extraction of functionality from structure wherever it can be found. It complements the remit of its host conference, Mathematics of Program Construction, by seeking to enrich the language and toolset available for specifications and programs alike. It is also a "small workshop" of the FP6 IST coordination action TYPES. Invited speakers Andrzej Filinski, Københavns Universitet John Power, University of Edinburgh Important dates * Submission of papers: 10 April 2006 * Notification of authors: 8 May 2006 * Camera-ready version: 5 June 2006 Topics Submissions are welcome on, but by no means restricted to, topics from the following partially computed coinductive list: * structured effectful computation * structured recursion * structured tree and graph operations * structured syntax with variable binding * structures for datatype-genericity * structures for search * structured representations of functions * structured manipulation of mathematical structure * structured <thunk> in functional programming Authors concerned about the suitability of a topic are very welcome to contact Conor McBride, ctm(at)cs.nott.ac.uk. Submission and publication Papers in pdf not exceeding 15 pages and adhering to the eWiC style must be submitted by 10 April 2006 via an online submission webpage. Papers must report previously unpublished work and not be submitted concurrently to another conference with refereed proceedings. Accepted papers must be presented at the workshop by one of the authors. The proceedings of MSFP 2006 will be published in the Electronic Workshops in Computing (eWiC) series of the British Computer Society, http://ewic.bcs.org/. After the workshop, the authors of the best papers will be invited to submit revised and expanded versions to a special issue of the Journal of Functional Programming from Cambridge University Press. Programme committee Yves Bertot, INRIA Sophia Antipolis Marcelo Fiore, University of Cambridge Masahito Hasegawa, Kyoto University Graham Hutton, University of Nottingham Paul Levy, University of Birmingham Andres Löh, Universitt Bonn Christoph Lüth, Universitt Bremen Conor McBride, University of Nottingham (co-chair) Marino Miculan, Università degli Studi di Udine Randy Pollack, University of Edinburgh Amr Sabry, Indiana University Tarmo Uustalu, Institute of Cybernetics (co-chair) Main conferences MSFP 2006 is a satellite workshop of the 8th International Conference on Mathematics on Program Construction, MPC 2006, to take place 3-5 July. Co-located with MPC 2006, the 11th International Conference on Algebraic Methodology and Software Technology, AMAST 2006, will follow 5-8 July. Venue Kuressaare (pop. 16000) is the main town on Saaremaa, the second-largest island of the Baltic Sea. Kuressaare is a charming seaside resort on the shores of the Gulf of Riga highly popular with Estonians as well as visitors to Estonia. The scientific sessions of MPC/AMAST 2006 will take place at Saaremaa Spa Hotel Meri, one among the several new spa hotels in the town. The social events will involve a number of sites, including the 14th-century episcopal castle. Accommodation will be at Saaremaa Spa Hotels Meri and Rüütli. To get to Kuressaare and away, one must pass through Tallinn (pop. 402000), Estonia's capital city. Tallinn is famous for its picturesque medieval Old Town, inscribed on UNESCO's World Heritage List. TYPES support MSFP 2006 is an official workshop of the EU FP6 IST coordination action TYPES. Participants from TYPES sites/subsites may use project funds to cover their travel and participation. Local organizers MPC/AMAST 2006 is organized by Institute of Cybernetics, a research institute of Tallinn University of Technology. The local organizers are Tarmo Uustalu (chair), Monika Perkmann, Juhan Ernits, Ando Saabas, Olha Shkaravska, Kristi Uustalu. Contact email address of the local organizers: mpc06(at)cs.ioc.ee.

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RE: [Haskell] Compilation of big, computed tables
by Simon Peyton-Jones 23 Feb '06

23 Feb '06

http://haskell.org/haskellwiki/GHC:FAQ (search for cse) | -----Original Message----- | From: haskell-bounces(a)haskell.org [mailto:haskell-bounces@haskell.org] On Behalf Of Bjorn Lisper | Sent: 23 February 2006 10:28 | To: haskell(a)list.mightyreason.com | Cc: Haskell(a)haskell.org | Subject: Re: [Haskell] Compilation of big, computed tables | | Chris Kuklewicz: | >Stefan Karrmann wrote: | >> Dear all, | >> | >> can ghc compile huge tables into efficient code if they are constant at | >> compile time? | >> | >> Two examples may clearify the question: | >> | >> big1 :: UArray Int Char | >> big1 = array (0,1000) $! map (\i -> (i,toEnum i)) [0..1000] | >> | >> big2 = sum [0..10000]::Int -- == 50005000 == n*(n+1)/2 where n = 10000 | >> | > | >GHC does not compute such values are compile time because | >*) The computation may not finish in reasonable time (infinite/not halting) | >*) The computation may generate a run-time error and crash the compilation | >(divide by zero, pattern march failure, etc.) | >*) Haskell is supposed to be lazy, things are computed when needed, not before | | Does this mean that GHC does not evaluate constant subexpressions at | compile-time? Or does it evaluate only some subclass of surely terminating | and non-erroneous subexpressions at compile-time? | | Constant subexpression evaluation is a common compiler optimization | technique, so I would be a bit surprised if GHC does not do it. | | Björn LIsper | _______________________________________________ | Haskell mailing list | Haskell(a)haskell.org | http://www.haskell.org/mailman/listinfo/haskell

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