July 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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type class instance selection & search
by Conal Elliott 01 Aug '07

01 Aug '07

I keep running into situations in which I want more powerful search in selecting type class instances. One example I raised in June, in which all of the following instances are useful. > instance (Functor g, Functor f) => Functor (O g f) where > fmap h (O gf) = O (fmap (fmap h) gf) > instance (Cofunctor g, Cofunctor f) => Functor (O g f) where > fmap h (O gf) = O (cofmap (cofmap h) gf) > instance (Functor g, Cofunctor f) => Cofunctor (O g f) where > cofmap h (O gf) = O (fmap (cofmap h) gf) > instance (Cofunctor g, Functor f) => Cofunctor (O g f) where > cofmap h (O gf) = O (cofmap (fmap h) gf) My understanding is that this sort of instance collection doesn't work together because instance selection is based only on the matching the head of an instance declaration (part after the "=>"). I'm wondering why not use the preconditions as well, via a Prolog-like, backward-chaining search for much more flexible instance selection? Going further, has anyone investigated using Prolog as a model for instance selection? Better yet, how about LambdaProlog ( http://www.lix.polytechnique.fr/Labo/Dale.Miller/lProlog) which generalizes from Horn clauses to (higher-order) hereditary Harrop formulas, including (restricted but powerful) universals, implication, and existentials? Once search is in there, ambiguity can arise, but perhaps the compiler could signal an error in that case (i.e., if the ambiguity is not eliminated by further search pruning). My motivation: I've been playing with a programming style in which my type formulation leads to automatic construction of much of the code, thanks to use of Functor, Applicative, Monoid, and type composition. An example is http://haskell.org/haskellwiki/Applicative_data-driven_programming, and I'm trying now to do the same to create a much simpler implementation of Eros ( http://conal.net/papers/Eros) I think this programming style is what Conor was alluding to recently as "types don't just contain data, types explain data" (http://article.gmane.org/gmane.comp.lang.haskell.cafe/26520) (Conor: I hope you chime in.) My hunch is that this programming style tends to run up against the head-only instance matching mechanism and would work much better with a more powerful means of selecting instances. - Conal

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3-yr post for language person
by Simon Peyton-Jones 31 Jul '07

31 Jul '07

Tim Griffin is advertising a 3-year research associate position at the Cambridge Computer Lab, working on a project that seeks to design and implement a meta-language for the specification and implementation of correct Internet routing protocols. He says "A PL person would be perfect". Details here: http://www.admin.cam.ac.uk/offices/personnel/jobs/vacancies.cgi?job=2114 Simon

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APLAS 2007 call for poster presentations (Singapore, Nov 29 - Dec 1)
by Eijiro Sumii 31 Jul '07

31 Jul '07

CALL FOR POSTER PRESENTATIONS The Fifth ASIAN Symposium on Programming Languages and Systems (APLAS 2007) November 29 - December 1, 2007 Singapore http://flint.cs.yale.edu/aplas2007/ APLAS 2007 will include a poster session during the conference. The session aims to give students and researchers an opportunity to present their research to the community, and to get responses from other researchers. SCOPE: Poster presentations are sought in all areas of programming languages and systems, including (but not limited to): - semantics, logics, foundational theory - type systems, language design - program analysis, optimization, transformation - software security, safety, verification - compiler systems, interpreters, abstract machines - domain-specific languages and systems - programming tools and environments FORMAT: A space of A1 paper size (594 mm wide and 841 mm high) will be provided for each presentation. If you need more space, contact the poster chair (sumii AT ecei DOT tohoku DOT ac DOT jp). To prepare a good poster, search the Web for "poster presentation" and you will find many useful resources. REGISTRATION: Each presenter should e-mail a 1-2 page abstract in PDF or PostScript (including the title, authors, affiliations, and a summary of the work) to the poster chair (sumii AT ecei DOT tohoku DOT ac DOT jp) by September 14th, 2007. The program of the poster session will be announced by September 21st, 2007. We hope to accommodate every poster, but may restrict presentations (based on relevance and interest to the community) due to space constraints. IMPORTANT DATES: 1-2 page abstract September 14, 2007 notification September 21, 2007 conference November 29 - December 1, 2007 CONTACT: For questions or requests, please contact the APLAS 2007 poster chair, Eijiro Sumii (sumii AT ecei DOT tohoku DOT ac DOT jp).

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Latest AngloHaskell news and a request
by Philippa Cowderoy 30 Jul '07

30 Jul '07

Two pieces of news regarding AngloHaskell: 1) We've been offered WiFi access at Microsoft Research for any attendees who want it. We'll need a name, email address and company/institution affiliation where appropriate - see wiki for details. 2) We're being given lunch on Friday! Finally, a request: We're a little short on crashspace, and I suspect this is affecting who's able to show up. Could people who can only make it with crashspace (or who can only make one day without) add their names on the wiki? Is there anyone in the area able to offer people at least some space on a floor? Last year we had offers early, and I think this helped get plans moving. For those who could use the reminder, the wiki page is at http://www.haskell.org/haskellwiki/AngloHaskell Many thanks, and I hope to see you there! -- flippa(a)flippac.org Society does not owe people jobs. Society owes it to itself to find people jobs.

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Haskell->Erlang compiler, sort of
by Bulat Ziganshin 30 Jul '07

30 Jul '07

Hello haskell, http://blog.tornkvist.org/?id=1185571582964040 -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Call for Submissions - First Workshop on Languages and Tools for Parallel and Distributed Programming (LTPD 2007)
by heron_carvalho 30 Jul '07

30 Jul '07

------------------------------------------------------------ First Workshop on Languages and Tools for Parallel and Distributed Programming (LTPD 2007) http://computacao.ucpel.tche.br/ltpd/ Gramado, RS - Brazil Co-located with SBAC-PAD 2007 (24-27 October 2007) *** Submissão de artigos: 24 de Agosto *** ------------------------------------------------------------ The objective of this workshop is to bring together researchers working on the design and implementation of programming languages, tools and techniques for distributed, parallel and mobile programming. Submitted papers should present original research that is unpublished and not submitted elsewhere. We encourage the submission of work in progress, especially by MSc and PhD students. We plan to provide a friendly environment where researchers can discuss current and future trends in programming languages for parallel and distributed programming. Papers can be written in English, Portuguese and Spanish. Papers should have 4 pages, following the IEEE Computer Society Proceedings Manuscript Formatting Guidelines. All accepted papers will be published in the On-Line conference proceedings, and as a technical report. The SBAC-PAD organization will also publish the electronic proceedings in CD. We plan to publish selected high quality papers from the proceedings in a local brazilian journal. At least one author of an accepted paper must attend the workshop and all workshop attendees must be registered to SBAC-PAD. Topics of Interest ------ -- -------- Topics of interest include, but are not limited to: * Programming Multi-Core Machines * Coordination Languages * Concurrent and Parallel Garbage Collection * Type systems and semantics for parallel, distributed and mobile languages * Declarative parallel, distributed and mobile languages * Languages for mobile and ubiquitous computing * Calculi for Mobility and Concurrency * Design Patterns * Distributed Objects * Distributed Component Models * Mobile Agents Languages * Software issues for multicore or multithreaded processors Important Dates --------- ----- * Deadline for paper submission: August 24, 2007 * Accepted Papers Notification: September 10, 2007 * Camera-Ready Submission: September 17, 2007 Organizing Committee ---------- --------- André Rauber Du Bois (Chair) - UCPel Francisco Heron de Carvalho Junior (Chair)- UFC Program Committe ------- -------- Adenauer Correa Yammin - UCPel Alcides Calsavara - PUCPR Álvaro Freitas Moreira - UFRGS André Rauber Du Bois - UCPel André Santos - UFPE Claudio Fernando Resin Geyer - UFRGS Cristiano Vasconcellos - UFPel Francisco Heron De Carvalho Jr - UFC Hans-Wolfgang Loidl - LMU, Germany Iara Augustin - UFSM Jorge Luis Victoria Barbosa - Unisinos Marco Túlio de Oliveira Valente - PUC-MG Phil Trinder - Heriot-Watt University, UK Rafael Dueire Lins - UFPE Ricardo Corrêa - UFC

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ANN: hpodder 1.0.0
by John Goerzen 29 Jul '07

29 Jul '07

Hi, I'm pleased to announce version 1.0.0 of hpodder, the command-line podcatcher (podcast downloader) that just happens to be written in everyone's favorite language. You can get it from: http://software.complete.org/hpodder Version 1.0.0 sports a new mechanism for detecting and disabling feeds or episodes that repeatedly result in errors, updates to the Sqlite database schema, and several bugfixes. -- John

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