June 2007 - Haskell - Haskell.org

Announcing Djinn, version 2004-12-11, a coding wizard
by Lennart Augustsson 07 Apr '11

07 Apr '11

Howdy, y'all! I've written a small program that takes a (Haskell) type and gives you back a function of that type if one exists. It's kind of fun, so I thought I'd share it. It's probably best explained with a sample session. calvin% djinn Welcome to Djinn version 2005-12-11. Type :h to get help. # Djinn is interactive if not given any arguments. # Let's see if it can find the identity function. Djinn> f ? a->a f :: a -> a f x1 = x1 # Yes, that was easy. Let's try some tuple munging. Djinn> sel ? ((a,b),(c,d)) -> (b,c) sel :: ((a, b), (c, d)) -> (b, c) sel ((_, v5), (v6, _)) = (v5, v6) # We can ask for the impossible, but then we get what we # deserve. Djinn> cast ? a->b -- cast cannot be realized. # OK, let's be bold and try some functions that are tricky to write: # return, bind, and callCC in the continuation monad Djinn> type C a = (a -> r) -> r Djinn> returnC ? a -> C a returnC :: a -> C a returnC x1 x2 = x2 x1 Djinn> bindC ? C a -> (a -> C b) -> C b bindC :: C a -> (a -> C b) -> C b bindC x1 x2 x3 = x1 (\ c15 -> x2 c15 (\ c17 -> x3 c17)) Djinn> callCC ? ((a -> C b) -> C a) -> C a callCC :: ((a -> C b) -> C a) -> C a callCC x1 x2 = x1 (\ c15 _ -> x2 c15) (\ c11 -> x2 c11) # Well, poor Djinn has a sweaty brow after deducing the code # for callCC so we had better quit. Djinn> :q Bye. To play with Djinn do a darcs get http://darcs.augustsson.net/Darcs/Djinn or get http://darcs.augustsson.net/Darcs/Djinn/Djinn.tar.gz Then just type make. (You need a Haskell 98 implementation and some libraries.) And then start djinn. For the curious, Djinn uses a decision procedure for intuitionistic propositional calculus due to Roy Dyckhoff. It's a variation of Gentzen's LJ system. This means that (in theory) Djinn will always find a function if one exists, and if one doesn't exist Djinn will terminate telling you so. This is the very first version, so expect bugs. :) Share and enjoy. -- Lennart

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Haskell-mode 2.0
by Stefan Monnier 02 Feb '09

02 Feb '09

I have recently taken over maintainership of Haskell-mode, and after making a bunch of changes, I figured it would be a good idea to make a new release. You can find this new release at: http://www-perso.iro.umontreal.ca/~monnier/elisp/ If you think it should also be found at http://www.haskell.org/haskell-mode/, then please tell John Peterson to get back to me (my email to him seem to go straight to the bitbucket. John?). This release has several changes that have all been only lightly tested, especially w.r.t compatibility with various Emacsen. See appended the NEWS file that describes some of the notewirthy changes. Stefan Changes since 1.45: * keybindings C-c <char> have been replaced by C-c C-<char> so as not to collide with minor modes. * The following modules are now automatically activated without having to add anything to haskell-mode-hook: haskell-font-lock (just turn on global-font-lock-mode). haskell-decl-scan (just bind `imenu' to some key). * In recent Emacsen, haskell-doc hooks into eldoc-mode. * haskell-hugs and haskell-ghci are superceded by inf-haskell. * Indentation rules have been improved when using layout inside parens/braces. * Symbols like -> and \ can be displayed as actual arrows and lambdas. See haskell-font-lock-symbols. * Tweaks to the font-lock settings. Among other things paren-matching with things like \(x,y) should work correctly now. * New maintainer <monnier(a)gnu.org>.

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The real Monad Transformer
by Henning Thielemann 13 Nov '08

13 Nov '08

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

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Anglo Haskell 2007, call for participation
by Neil Mitchell 28 Jun '07

28 Jun '07

Hi, People have proposed that we have another AngloHaskell this year. These events are being coordinated via the wiki: http://www.haskell.org/haskellwiki/AngloHaskell The current thoughts are to have a day of talks on Friday, followed by a day of social activities (punting perhaps, maybe some coding) on Saturday. The probable venue is MSR Cambridge, and the date is probably either August or early September. Can everyone interested in going please annotate the wiki with their time constraints, and intention to participate. This is NOT an academic conference. Everyone is welcome to attend, there is no fee. Everyone is invited to offer a talk. Thanks Neil and Philippa

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External reviews
by Gabriele Keller 27 Jun '07

27 Jun '07

If you prefer to have two separate review forms, I can add dummy PC members to the PC for this purpose. So, please let me know if you want me to set it up for you, and for which papers you would submit two reviews. However, I would also need an email address different to the address of the main account (the system doesn't let me add two PC member with the same address) Gabi

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FWD: PADL 2008: Call for Papers
by Simon Marlow 26 Jun '07

26 Jun '07

[posting on behalf of Gopal Gupta <gupta(a)utdallas.edu>] CALL FOR PAPERS!!! Tenth International Symposium on Practical Aspects of Declarative Languages 2008 (PADL '08) http://www.ist.unomaha.edu/padl2008/ San Francisco, USA January 7-8, 2008 Co-located with ACM POPL'08 Declarative languages build on sound theoretical bases to provide attractive frameworks for application development. These languages have been successfully applied to vastly different real-world situations, ranging from data base management to active networks to software engineering to decision support systems. New developments in theory and implementation have opened up new application areas. At the same time, applications of declarative languages to novel problems raises numerous interesting research issues. Well-known questions include designing for scalability, language extensions for application deployment, and programming environments. Thus, applications drive the progress in the theory and implementation of declarative systems, and benefit from this progress as well. PADL is a forum for researchers and practitioners to present original work emphasizing novel applications and implementation techniques for all forms of declarative concepts, including, functional, logic, constraints, etc. Topics of interest include: * innovative applications of declarative languages; * declarative domain-specific languages and applications; * practical applications of theoretical results; * new language developments & their impact on applications; * evaluation of implementation techniques on practical applications; * novel uses of declarative languages in the classroom; and * practical experiences PADL 08 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages. PADL 08 will be co-located with the ACM POPL. IMPORTANT DATES AND SUBMISSION GUIDELINES Paper Submission: August 24, 2007 Notification: September 27, 2007 Camera-ready: October 23, 2007 Symposium: January 7-8, 2008 Authors should submit an electronic copy of the full paper (written in English) in Postscript (Level 2) or PDF. Papers must be no longer than 15 pages, written in 11-point font and with single spacing. Since the final proceedings will be published as Lecture Notes in Computer Science by Springer Verlag, authors are strongly encouraged to use the LNCS paper formatting guidelines for their submission. Each submission must include on its first page the paper title; authors and their affiliations; contact author's email and postal addresses, telephone and fax numbers, abstract, and three to four keywords. The keywords will be used to assist us in selecting appropriate reviewers for the paper. If electronic submission is impossible, please contact the program chair for information on how to submit hard copies. MOST PRACTICAL PAPER AWARD The Most Practical Paper award will be given to the submission that is judged by the program committee to be the best in terms of practicality, originality, and clarity of presentation. The program committee may choose not to make an award, or to make multiple awards. Contacts: For information about papers and submissions, please contact the Program Chair: Paul Hudak PC co-Chair - PADL 2008 Department of Computer Science Yale University P.O. Box 208285 New Haven, CT 06520 - 8285 Email: hudak(a)cs.yale.edu David S. Warren PC co-Chair - PADL 2008 Department of Computer Science Stony Brook University Stony Brook, NY Email: warren(a)cs.sunysb.edu For other information about the conference, please contact: Hai-Feng Guo General Chair - PADL 2008 Department of Computer Science College of Information Science & Technology University of Nebraska at Omaha Omaha, NE, U.S.A. Email: haifengguo(a)mail.unomaha.edu Sponsored by: COMPULOG Americas (http://www.cs.nmsu.edu/~complog) and University of Nebraska at Omaha

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Building extra-libs (packages text, data, util, lang)
by bft 25 Jun '07

25 Jun '07

Hello I am trying to install FRUIT (Functional Reactive User Interface Toolkit - http://www.haskell.org/fruit/) I didn't succeed when building Greencard (2.03 or 2.05) because (I suppose) the packages text, data, util, lang were not found with the ghc-6.6.1haskell compiler. A part of the error generated is : "Glasgow Haskell Compiler, Version 6.6.1, for Haskell 98, compiled by GHC version 6.6.1 Using package config file: /home/bfotsing/lib/ghc-6.6.1/package.conf Using package config file: /home/bfotsing/.ghc/i386-linux-6.6.1/package.conf *** Deleting temp files: Deleting: *** Deleting temp dirs: Deleting: ghc-6.6.1: unknown package: text" I don't know where to get those packages or (maybe) how to build them since I didn't find them in the ghc extra-libs ( http://www.haskell.org/ghc/download_ghc_661.html) Thanks for your help BFT

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Building extra-libs (packages text, data, util, lang)
by FOTSING TALLA Bernard 24 Jun '07

24 Jun '07

> Hello > I am trying to install FRUIT (Functional Reactive User Interface Toolkit - > http://www.haskell.org/fruit/) > I didn't succeed when building Greencard (2.03 or 2.05) because (I suppose) > the packages text, data, util, lang were not found with the > ghc-6.6.1 haskell compiler. > A part of the error generated is : > "Glasgow Haskell Compiler, Version 6.6.1, for Haskell 98, compiled by GHC > version 6.6.1 > Using package config file: /home/bfotsing/lib/ghc-6.6.1/package.conf > Using package config file: /home/bfotsing/.ghc/i386-linux-6.6.1/package.conf > *** Deleting temp files: > Deleting: > *** Deleting temp dirs: > Deleting: > ghc-6.6.1: unknown package: text" > I don't know where to get those packages or (maybe) how to build them since > I didn't find them in the ghc extra-libs ( > http://www.haskell.org/ghc/download_ghc_661.html) > Thanks for your help > BFT Hello I commented the part of code concerned in order to ignore those options, and the building failed again with this message : Casm.lhs:479:13: Couldn't match expected type `GHC.Ptr.Ptr t' against inferred type `[Char]' In the first argument of `ptext', namely `"C_RETURN(nodeptr);"' In the second argument of `($$)', namely `ptext "C_RETURN(nodeptr);"' In the first argument of `ppBlock', namely `(((ccode $$ (ppAssign "nodeptr" pprResult)) $$ end) $$ (ptext "C_RETURN(nodeptr);"))' make[1]: *** [Casm.o] Erreur 1 make[1]: quittant le répertoire « /home/bfotsing/gc-2.05/src » Can you help me?

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Class type constraining?
by Hugo Pacheco 22 Jun '07

22 Jun '07

Hi, I have a set of functor definitions with corresponding instances newtype Id a = Ident {unIdent :: a} deriving Eq newtype K b a = Const {unConst :: b} deriving Eq instance Functor Id where fmap f (Ident x) = Ident $ f x instance Functor (K a) where fmap f (Const x) = Const x (...) And a class that creates a representation b for a functor f a: class Functor f => C f a b | f a -> b where ftest :: f a -> b instance C Id a a instance C (K b) a b I want to write some function test :: (C f a b) => (a -> b) test = ftest . undefined But, as expected, the type checker claims not to satisfy the context, since the function may be valid for any representable functor, as long as it has an instance. What I would want is to constrain the set of functors that the class applies to, for which I have all the required instances. Is it possible in Haskell? Sorry if this explanation is confusing. Thanks in advance, hugo

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ANNOUNCE: Haskell Program Coverage 0.4
by Andy Gill 22 Jun '07

22 Jun '07

I am happy to announce release 0.4 of Hpc, a tool for Haskell developers. Hpc is a tool-kit to record and display Haskell Program Coverage. Hpc includes tools that instrument Haskell programs to record program coverage, run instrumented programs, and display the coverage information obtained. This version includes many changes since 0.2, including a small DSL for expressing coverage "holes". More details can be found on the Hpc web-page. http://projects.unsafePerformIO.com/hpc Feedback and feature requests are encouraged. Andy Gill

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