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Fundep broken in GHC 6.6
by Yitzchak Gale 16 Nov '06

16 Nov '06

Hi, The following class declaration worked in GHC 6.4. I recently upgraded to 6.6 (following Debian), and now it is broken. class Error e => Game b mv e | b -> mv e where newBoard :: MonadState b m => m () ... Since MonadState has the fundep m -> b, the type of newBoard fully specifies all of the class parameters. And this worked fine in GHC 6.4. But GHC 6.6 complains: The class method `newBoard' mentions none of the type variables of the class Game b mv e When checking the class method: newBoard :: m () In the class declaration for `Game' Any ideas? Thanks, Yitz

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HaskellWiki Style Help
by Ashley Yakeley 15 Nov '06

15 Nov '06

If you're interested in improving the CSS for HaskellWiki, please go to <http://haskell.org/haskellwiki/HaskellWiki:Community#Style_Help>. The only requirements are knowledge of CSS and an ability to use MediaWiki. More than one person would be ideal. At Simon PJ's request, I have also turned on numbered headings for when not logged in. Logged-in users can set this option at Preferences -> Misc. I'm not sure it's an improvement, however; it makes the front page look a bit odd. -- Ashley Yakeley

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ANNOUNCE: LocH, source locations in error, trace, and exceptions
by dons＠cse.unsw.edu.au 14 Nov '06

14 Nov '06

The topic of improving exception diagnosis in Haskell is hot at the moment, and I'm pleased to announce the release of LocH, a small Haskell module providing source location-specific error messages and debugging strings for Haskell code. It uses the compiler-expanded 'assert' token, rather than cpp or m4, to provide a lightweight approach to generating source locations. No preprocessor is required. The code is available under a BSD license. The LocH home: http://www.cse.unsw.edu.au/~dons/loch.html The API: http://www.cse.unsw.edu.au/~dons/loch/Debug-Trace-Location.html Example usage: import Debug.Trace.Location main = trace assert "Starting ..." $ do print 1 trace assert "Finished" $ do print 2 let x = check assert $ head ([] :: [Int]) print x Will produce: $ ./a.out A.hs:4:10-15: Starting ... 1 A.hs:6:10-15: Finished 2 a.out: A.hs:8:18-23: Prelude.head: empty list LocH provides located versions of trace, failure, as well as check and checkIO to wrap exception-throwing pure and IO code. May all your exceptions be located, Don

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ANN: Safe library, 0.1
by Neil Mitchell 14 Nov '06

14 Nov '06

Hi, I am hereby releasing the Safe library, 0.1. http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php#safe (darcs repo, haddock documentation, cabal file, BSD3 licensed) People often have a problem with pattern match errors, and the only helpful message they get is: "pattern match error, head []". The Safe library hopes to eliminate some of the frustration this causes. Within the Safe library there are 3 different forms of head: headNote - takes an extra parameter which gives extra information - such as the function that is calling head, or a useful reminder to the programmer why head might be failing. headDef - takes an extra parameter being the default value, to return on the empty list. headMay - wrap the result in a Maybe, returning Nothing for failure. There are also a large number of other wrapped functions, which may prove useful. A variant of this library has been in use one of my projects (Catch) for some time, and has saved a lot of debugging headaches. I have found an effective way of debugging is to use the normal head function, and then when an error occurs start replacing instances of head with headNote until the error is diagnosed. Once the headNote's have been inserted, leave them, to help next time. Any comments or suggestions are welcome. Thanks Neil

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[ANN] Call for participation: TLDI'07
by Francois Pottier 14 Nov '06

14 Nov '06

****************************************************************************** The 2007 ACM SIGPLAN Workshop on Types in Language Design and Implementation (TLDI'07) Affiliated with the 34th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages (POPL'07) Call for Participation http://www.cs.berkeley.edu/~necula/tldi07/ ****************************************************************************** Preliminary programme Invited talks: Kathleen Fisher (AT&T Research) Conor McBride (University of Nottingham) Accepted papers: A Garbage-Collecting Typed Assembly Language Chris Hawblitzel, Heng Huang, Lea Wittie and Juan Chen A graphical presentation of MLF types with a linear-time unification algorithm Didier Rémy and Boris Yakobowski An Open Framework for Foundational Proof-Carrying Code Xinyu Feng, Zhaozhong Ni, Zhong Shao and Yu Guo Modular Information Hiding and Type-Safe Linking for C Saurabh Srivastava, Michael Hicks and Jeffrey Foster Semantics of an Effect Analysis for Exceptions Nick Benton and Peter Buchlovsky System F with Type Equality Coercions Martin Sulzmann, Manuel Chakravarty, Simon Peyton Jones and Kevin Donnelly ****************************************************************************** Scope The role of types and proofs in all aspects of language design, compiler construction, and software development has expanded greatly in recent years. Type systems, type analyses, and formal deduction have led to new concepts in compilation techniques for modern programming languages, verification of safety and security properties of programs, program transformation and optimization, and many other areas. In light of this expanding role of types, the ACM SIGPLAN Workshop on Types in Language Design and Implementation (TLDI'07) follows five previous International Workshops on types in compilation and language design (TIC'97, TIC'98, TIC'00, and TLDI'03 and TLDI'05), with the hope of bringing together researchers to share new ideas and results in this area. ****************************************************************************** General Chair François Pottier INRIA Rocquencourt BP 105 78153 Le Chesnay Cedex FRANCE francois.pottier(a)inria.fr Program Chair George Necula University of California 783 Soda Hall Berkeley, CA 94720 necula(a)cs.berkeley.edu Program Committee Damien Doligez, INRIA Peter Lee, Carnegie Mellon University Andrew Kennedy, Microsoft Research, Cambridge Naoki Kobayashi, Tohoku University George Necula (chair), University of California, Berkeley Randy Pollack, Edinburgh University Norman Ramsey, Harvard University David Tarditi, Microsoft Research, Redmond Stephanie Weirich, University of Pennsylvania Hongwei Xi, Boston University

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Haskell Weekly News: November 14, 2006
by dons＠cse.unsw.edu.au 13 Nov '06

13 Nov '06

--------------------------------------------------------------------------- Haskell Weekly News http://haskell.org/haskellwiki/HWN Issue 49 - November 14, 2006 --------------------------------------------------------------------------- Welcome to issue 49 of HWN, a weekly newsletter covering developments in the Haskell community. This week we see the announcement of a Haskell to Javascript compiler project, and the overhaul of GHC's typeclass machinery is complete. Announcements * Compiling Haskell to Javascript: YCR2JS. Dimitry Golubovsky [1]announced Ycr2js, a sub-project within the [2]York Haskell Compiler (Yhc) project. It is aimed to create a tool to convert an arbitrary Haskell program into Javascript which in turn may be executed in any Web browser. With great amount of help from the Yhc Team, the converter has been integrated into the Yhc project, and initial stage of coding and development has been completed. [3]More documentation. 1. http://article.gmane.org/gmane.comp.lang.haskell.general/14471 2. http://darcs.haskell.org/yhc 3. http://haskell.org/haskellwiki/Yhc/Javascript * System.FilePath 0.10. Neil Mitchell [4]announced System.FilePath 0.10, which hopefully is pretty close to final. [5]This library manipulates FilePath's correctly on both Posix and Windows. 4. http://article.gmane.org/gmane.comp.lang.haskell.general/14467 5. http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php#filepath * Major typeclass overhaul. Simon Peyton-Jones [6]mentioned that for some time he has been promising an overhaul of GHC's type inference machinery to fix the interactions between type classes and GADTs. This overhaul has now been completed, and user-visible changes are summarised, including: GHC's type inference becomes complete, the restriction that every constraint in a type signature must mention at least one of the quantified type variables is lifted, dictionaries are packaged in data constructors and the proper interaction between GADTs and type classes is now respected. 6. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/11192 * Implementing the lambda calculus. Lennart Augustsson [7]wrote about implementing interpreters for the lambda-calculus in Haskell, to [8]experiment with different implementation methods. 7. http://article.gmane.org/gmane.comp.lang.haskell.cafe/16490 8. http://darcs.augustsson.net/Darcs/Lambda/ * Great language shootout: reloaded. Don Stewart [9]mentioned that now [10]GHC 6.6 is available on the shootout machines, the time has come to improve the existing [11]language shootout entries. Improvements can be posted to the [12]wiki for review. 9. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/16454/focus=16454 10. http://haskell.org/ghc 11. http://shootout.alioth.debian.org/ 12. http://www.haskell.org/haskellwiki/Great_language_shootout Haskell' This section covers the [13]Haskell' standardisation process. * [14]Overloading string literals * [15]Annotation systems 13. http://hackage.haskell.org/trac/haskell-prime 14. http://thread.gmane.org/gmane.comp.lang.haskell.prime/1882/focus=1882 15. http://thread.gmane.org/gmane.comp.lang.haskell.prime/1889/focus=1889 Libraries This week's proposals and extensions to the [16]standard libraries. * [17]Adding Kleisli composition to Control.Monad * [18]Add ranged sets * [19]Add unsafeCoerce 16. http://haskell.org/haskellwiki/Library_submissions 17. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/5640/focus=5640 18. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/5635/focus=5635 19. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/5611/focus=5611 Discussion * Choosing a Haskell GUI library. Bulat Ziganshin [20]asked for advice on which Haskell gui library to use. Several suggestions were made. 20. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/16497/focus=16497 Conference roundup Asian Symposium on Programming Languages and Systems (APLAS 2006) * Type Processing by Constraint Reasoning. Peter Stuckey. [21]Paper. * Principal Type Inference for GHC-Style Multi-Parameter Type Classes. Martin Sulzmann, Tom Schrijvers and Peter J Stuckey. [22]Paper. * Automatic Testing of Higher Order Functions. Pieter Koopman and Rinus Plasmeijer. [23]Paper. 21. http://www.cs.mu.oz.au/~pjs/papers/aplas06i.pdf 22. http://www.comp.nus.edu.sg/~sulzmann/publications/ghc-mptc-inf.ps 23. http://www.st.cs.ru.nl/papers/2006/koop2006-TestingOfHigherOrderFunctionsAP… Jobs * Research position in spatial cognition (Haskell-related). Till Mossakowski [24]announced the availability of a Doctoral Research Assistant / Postdoctoral Researcher position at the Universit�t Bremen, concerned with classification and formalization of qualitative spatial calculi, relations among these calculi, spatial ontologies, and route graphs. [25]More information. 24. http://article.gmane.org/gmane.comp.lang.haskell.general/14469 25. http://www.sfbtr8.uni-bremen.de/i4.html Blog noise [26]Haskell news from the blogosphere. * [27]Getting real with Haskell * [28]A Simple RPN Calculator in Haskell * [29]One more grunt trying to learn Haskell * [30]Testing Telecoms Software with Quviq QuickCheck * [31]Quviq QuickCheck: A new automated testing tool * [32]My first Haskell adventure game! 26. http://planet.haskell.org/ 27. http://therning.org/magnus/archives/219 28. http://jcreigh.blogspot.com/2006/11/simple-rpn-calculator-in-haskell.html 29. http://monad.carnalreason.org/wordpress/?p=4 30. http://lambda-the-ultimate.org/node/1827 31. http://blog.lab49.com/?p=703 32. http://jpmoresmau.blogspot.com/2006/11/my-first-haskell-adventure-game.html Quotes of the Week * dylan: I remember being introduced to lambdas (in perl) from the programming perl, 2nd edition book. I used them heavily ever since... like some kind of cocaine addiction. * jdunck: What's your safeword? * sketerpot: With very strict typing, you need an *unsafe*word. * Binkley: Can you represent 'more moronic than Slashdot' with a 32-bit integer? * Robert Dockins: A Turing-complete type-checker isn't enough! Our work is not complete until the parser is a universal machine as well! * dons: Disable the type checker in GHC for 6 months and we'd have 5 Haskell debuggers by the end of it. * lennart: System Verilog is one of the worst 'designs' I've ever seen. So I bet it will be popular * lispy: The biggest reason most developers I know don't fix a bug is because they don't know it exists yet * monochrom: Time flies like an arrow. Fruit flies like a banana. Syntax rules like a macro * robreim: [on the new #haskell lojban channel] Great, now we've got to start an IRC channel for lojban-speaking, Haskell-coding anarchists * syntaxfree: Yes, Wadlerman: Prince of Funktions Code Watch * 2006-11-09 17:01:33 GMT. Claus Reinke. [33]Syntax patch for lambda-match. 33. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/17645 * 2006-11-06 21:27:30 GMT. Lennart Kolmodin. [34]New ghc-pkg option 'check'. A patch for ghc-pkg show broken packages (due to missing dependencies) with a new command 'check', and also indicate broken packages when using the command 'list'. 34. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/17656 * 2006-11-10 13:43:26 GMT. Simon Peyton Jones. [35]Use implication constraints to improve type inference. 35. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/17665 * 2006-11-13 09:36:19 GMT. Simon Peyton Jones. [36]Add literal-shift rewrite rules. 36. http://article.gmane.org/gmane.comp.lang.haskell.cvs.ghc/17705 About the Haskell Weekly News Each week, new editions are posted to [37]the Haskell mailing list as well as to [38]the Haskell Sequence and [39]Planet Haskell. [40]RSS is also available, and headlines appear on [41]haskell.org. The Haskell Weekly News is also [42]available in Spanish translation. To help create new editions of this newsletter, please see the [43]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 37. http://www.haskell.org/mailman/listinfo/haskell 38. http://sequence.complete.org/ 39. http://planet.haskell.org/ 40. http://sequence.complete.org/node/feed 41. http://haskell.org/ 42. http://haskell.org/haskellwiki/HWN/es 43. http://haskell.org/haskellwiki/HWN

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ANN YCR2JS, a Yhc Core to Javascript Converter
by Dimitry Golubovsky 13 Nov '06

13 Nov '06

Hi, Ycr2js is a sub-project within the York Haskell Compiler (Yhc) project. It is aimed to create a tool to convert an arbitrary Haskell program into Javascript which in turn may be executed in any Web browser. I am pleased to announce that, with great amount of help from the Yhc Team, the converter has been integrated into the Yhc project, and initial stage of coding and development has been completed. Interested members of the Haskell community are invited to experiment with the Converter. It can be obtained with current Yhc snapshot from http://darcs.haskell.org/yhc At this point, it is possible to convert a Haskell program into Javascript and create a XHTML page for viewing in a Web browser. No framework is available to access DOM in type safe way, and/or support for AJAX. Not all low-level primitives have been mapped to Javascript or optimized for the Javascript environment. These are tasks for next stages and will be worked on in near future. It was by no means only my idea to generate Javascript from Haskell. Several people expressed this idea earlier in blogs and mailing lists. I was interested in this myself, and just decided to go ahead and implement it. Documentation (partially written) is available: http://haskell.org/haskellwiki/Yhc/Javascript At the moment of this announce, there is one live demo: http://darcs.haskell.org/yhc/web/jsdemos/Echo.html also referred to from the Wiki page mentioned. Type any text in the input field provided, and see it echoed right above after Enter is pressed. Just for fun, type any decimal number and see it converted to a Roman number, and vice versa. Roman numerals module (C) Malcolm Wallace, originally from ftp://ftp.cs.york.ac.uk/pub/haskell/contrib/Roman.hs On not so fast computers, the demo may show some delays (e. g. 3 - 5 seconds on a 375 MHz Intel Celeron, Netscape7, Linux) between the text is typed and echoed (mostly due to Roman number conversion). This is being worked on. Ycr2js is work in progress. What is most needed is users feedback that would help improve it. Any feedback will be greatly appreciated. Thanks everyone who helped me in any way. Feel free to contact me at golubovsky(a)gmail.com -- Dimitry Golubovsky Anywhere on the Web

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Research position in spatial cogntion (Haskell-related)
by Till Mossakowski 10 Nov '06

10 Nov '06

1 Doctoral Research Assistant / Postdoctoral Researcher SFB/TR 8 project I4-[SPIN], Universität Bremen (TVL 13, approx. € 35,000 to € 50,000 p.a. gross) The research project I4-[SPIN] is concerned with classification and formalization of qualitative spatial calculi, relations among these calculi, spatial ontologies, and route graphs. Research tasks include both further development of the mathematical theory, the formalization and verification of critical results (like composition tables) using suitable specification languages and theorem proving tools, as well as further enhancement of these tools. The goal is to obtain both a trustworthy and efficient framework for qualitative spatial reasoning, which is applicable to reasoning tasks occurring in interactive wheelchair and robot navigation. The applicant should have a degree in computer science or in a related field (diploma, master's, or Ph.D.). Strong interest in formal methods and in interdisciplinary collaboration is expected. Especially, the applicant should have qualifications and/or interests in some of the following fields: . Qualitative spatial reasoning . Formal methods and theorem proving . Category theory . Functional programming (Haskell) We offer the opportunity to gain research experience in a modern and enthusiastic research environment with strong interdisciplinary and international links. Responsibilities include project work and research, publication of research results, supervision of student projects, participation in the activities of the SFB/TR 8, and contribution to research proposals. The position is available immediately / from January 2007 until the end of 2010. Extension is possible. Application deadline: 01 December 2006 (or until a suitable candidate is found). Universität Bremen is an equal opportunity employer. Women are especially encouraged to apply. Handicapped applicants with equal qualifications will be given preferential treatment. More information about this project can be found at www.sfbtr8.uni-bremen.de/i4. The Transregional Collaborative Research Center SFB/TR 8 Spatial Cognition: Reasoning, Action, Interaction at the Universities of Bremen and Freiburg, Germany pursues interdisciplinary long-term research in Spatial Cognition. Particular emphasis is given to: . Spatial Reasoning: Knowledge representation, human spatial thinking, computational modeling, diagrammatic reasoning, cognitive and computational complexity, qualitative spatio-temporal calculi; . Action in Space: Cognitive robotics, explorative localization and mapping, robot navigation, human navigation and wayfinding, sensorimotor representations of spatio-temporal structures, embodied cognition; . Communication and Interaction in Space: Formal methods, spatial and linguistic onto¬logies, computational linguistics, environmental cognition, integration of spatial methods. A description of the current research projects of the SFB/TR 8 can be found at www.sfbtr8.uni-bremen.de The SFB/TR 8 is funded by the German Research Foundation (DFG). Please address questions about the position and send your application (preferably by email) to: Dr. Till Mossakowski <tm(a)sfbtr8.uni-bremen.de> SFB/TR 8 - Spatial Cognition Universität Bremen P.O. Box 330 440 28334 Bremen / Germany -- Till Mossakowski Office: Phone +49-421-218-64226 DFKI Lab Bremen Cartesium Fax +49-421-218-9864226 Robert-Hooke-Str. 5 Enrique-Schmidt-Str. 5 till(a)tzi.de D-28359 Bremen Room 2.051 http://www.tzi.de/~till

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ANN: System.FilePath 0.10
by Neil Mitchell 08 Nov '06

08 Nov '06

Hi Haskell, ANNOUNCEMENT: I am hereby announcing System.FilePath 0.10, which hopefully is pretty close to final now. This library manipulates FilePath's correctly on both Posix and Windows. http://www-users.cs.york.ac.uk/~ndm/projects/libraries.php#filepath (Includes a darcs repo, a .tar.gz, haddock documentation etc) In this version I have made reasonably large changes: * Lots of functions gone (temporary file handling, canonicalization, drive manipulation, directory creation, directory enumeration) - pretty much down to only pure (non-IO methods) left. * 3 new methods (asFile, isFile, asDirectory - look up the docs for their meanings, but they are pretty small) * Renamed functions to follow the scheme replace/take/drop instead of set/get/drop - as suggested by Simon Marlow (since set/get implies state operations in Haskell) * Eliminated some duplicate functions (all functions are now different) * Better handling of some obscure corner cases, particularly on Windows with drive specifiers. * Even more automated testing (211 properties, 75 of them QuickCheck properties) This incorporates a large proportion of the suggestions that were applicable to my library and its underlying design decisions. COMPATIBILITY: Since this is a fairly large API change I have created System.FilePath.Compat, which is identical to the old API. As a quick fix import System.FilePath ==> import System.FilePath.Compat will work fine. In the haddock documentation of the Compat module I have included descriptions of what the new name of functions are (http://www-users.cs.york.ac.uk/~ndm/projects/filepath/System-FilePath-Compa…) I really don't like breaking things for existing users, but the Compat module should make it pretty easy to convert. If you do need any help with the migration email me and I'll help as required. The Compat module will remain around for the lifetime of this library, but will not be submitted for inclusion into base. FOLLOW UP DISCUSSION: As last time I released System.FilePath there was an 84 email long thread, I think its probably best if I try and structure the discussion this time so people can keep up with whats going on. Can we start a discussion on haskell-cafe related to this announcement, API names, API semantics and other general comments regarding this library. What should be removed? What should be added? What should be changed? I am very interested to see what people think, and to make something everyone can use. Please do not email on the main thread with anything related: * objections to the concept of putting a FilePath library in base (I'm not asking for that now, but I will be in future, feel free to flame me then) * objections to the concept of "type FilePath = String". This is the way it is (although feel free to start a separate discussion on this, if you want) THANKS: Thanks for everyone who gave suggestions and help on this (Lemmih, dcoutts, JaffaCake, the rest of the Yhc team, Issac, shapr, #haskell, Marc Webber, David House, Matt, lots of others). Thanks also to QuickCheck, without which this library would be much less reliable. Thanks Neil

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wxHaskell for GHC 6.6 and wxWidget 2.6.2
by Sukit Tretriluxana 07 Nov '06

07 Nov '06

Hi, I saw someone posting a comment (http://sequence.complete.org/node/214) about the build of wxHaskell for GHC 6.6 and wxWidget 2.6.2 but it's not currently hosted anywhere yet. Does anyone know where can I get the Windows binary build of it for the time being? Thanks, Ed

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