July 2006 - Haskell - Haskell.org

ANNOUNCE: HSP.Clientside 0.01
by Joel Björnson 25 Jul '06

25 Jul '06

This is a release of Summer of Code project HSP.Clientside 0.01. Some present features include : * An embedding of (typed) JavaScript language in Haskell. * A small combinator library for generating JavaScript code. * High-level interface to Ajax functionality. * Integration with HSP However, large parts of the code is still *highly* experimental and in big need of a clean up. For more information see www.dtek.chalmers.se/~bjornson/soc/<http://www.dtek.chalmers.se/%7Ebjornson/soc/> Darcs repository is available at darcs.haskell.org/SoC/hsp.clientside/ /Joel

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Internships on GHC and Haskell at MSR Cambridge
by Simon Peyton-Jones 25 Jul '06

25 Jul '06

Gentle Haskellers Would you be interested in working for three months at Microsoft Research, Cambridge, on a project related to GHC or Haskell? MSR Cambridge now takes interns *year-round*, not just in the summer months. Simon Marlow and I are keen to attract motivated and well-qualified folk to work with us on our research, and on improving or developing GHC. If you or one of your students is interested, you can find more details here http://hackage.haskell.org/trac/ghc/wiki/Internships Our next empty slot is the Oct-Dec period, but you are welcome to apply for some later period. Simon PJ PS: There are lots of other programming-language folk at MSR (F#, security, probabilistic languages...), and stuff beyond that (machine learning, systems and networks...); see http://research.microsoft.com/aboutmsr/labs/cambridge/

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ANNOUNCE: new FGL version (June 2006)
by Martin Erwig 25 Jul '06

25 Jul '06

FGL - A Functional Graph Library, Version: June 2006 ==================================================== A new release of the Functional Graph Library for Haskell is available at: http://eecs.oregonstate.edu/~erwig/fgl/haskell/ This release mainly fixes some bugs and improves a few function implementations. -- Martin

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ANN: TextRegexLazy 0.44
by Chris Kuklewicz 24 Jul '06

24 Jul '06

TextRegexLazy: The Text.Regex.Lazy replacement and enhancement for Text.Regex New Version: 0.44 Where: http://sourceforge.net/projects/lazy-regex Changes from 0.33 to 0.44 * Cabal * Compile with -Wall -Werror * Change DFAEngineFPS from Data.FastPackedString to Data.ByteString (still fairly untested) This was my first time packaging with cabal, and I am hoping it works for you. The tests have been cleaned up and now Cabal can run them. The change from FPS to ByteString was trivial. Question 1: What more would people want from a Regex engine for Data.ByteString? Question 2: Is there interest in getting this into an official release of the base libraries? The Compat module could at least replace or sit alongside the performance sink of the current Text.Regex code. -- Chris "I define UNIX as 30 definitions of regular expressions living under one roof." * Donald Knuth: Chapter 33 of the book Digital Typography, p. 649.

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ANN: monadic probabilistic functional programing
by Stefan Karrmann 21 Jul '06

21 Jul '06

Dear all, the library PFP by Martin Erwig is quite useful for probabilistic calculations. I have extended it to abstract monads, cabal and darcs, confer [1]. I cannot find a licence or legal note on the page of Martin Erwig. Therefore, I can legally only publish a patch. Unfortunatly, darcs does not provide a method to extract patches as far as I know. (Hints are welcomed.) As a result you can download a stripped down version of my darcs repository from [1]. How to create the complete repository is there described, too. [1] http://home.arcor.de/s.ka/haskell/pfp.html Kind regards, -- Stefan Karrmann

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using the ffi with callbacks
by Evan Martin 21 Jul '06

21 Jul '06

Suppose I have a C function like this: void register_callback( void (*callback_fcn)(void *data), void *callback_data, void (*free_fcn)(void *data)); I think this is pretty common in C libraries. The idea is that you can register a callback along with a pointer to some data to pass to it, and when the C code is done with the callback+data it'll call your free_fcn, again passing the same data. I'd like to wrap this in Haskell, allowing me to pass in a Haskell function as a callback. The tricky part is that to pass in Haskell functions, I need to use the FFI "wrapper" import, which means I need to later free them. But the only place I can free them is within the "free" callback, and I've just discovered this isn't allowed! To elaborate, the code setting this up looks something like this: callback_fcn <- ... -- get a FunPtr using "wrapper" from the ffi free_fcn <- ... -- as above -- the callback data is just stuff that needs freeing callback_data <- newStablePtr (callback_fcn, free_fcn) register_callback callback_fcn callback_data free_fcn And my plan was: within the function free_fcn wraps, free callback_fcn, free the StablePtr, and then finally free free_fcn itself. However, I discovered this thread, which indicates that having a function free its FunPtr is not allowed: http://www.haskell.org//pipermail/glasgow-haskell-users/2006-March/009907.h… I've poked around a bit online, and so far, the only solutions I've seen are 1) http://darcs.haskell.org/packages/GLUT/Graphics/UI/GLUT/Callbacks/Registrat… , which seems to involve three extra IORefs and unsafePerformIOs as well as an external library function for registering the scavenger. 2) http://darcs.haskell.org/gtk2hs/glib/System/Glib/ , which seems to either use a bunch of Haskell-specific C code I don't quite follow or use the self-delete pattern I described above (see mkFunPtrDestroyNotify in http://darcs.haskell.org/gtk2hs/glib/System/Glib/GObject.chs.pp) So my question is: is there really no simple way to support this pattern (which I would broadly refer to as "callbacks in general"), or am I missing something?

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PLAN-X 2007: Call for Papers and Demos
by Torsten Grust 21 Jul '06

21 Jul '06

[ Dear all, I'd love to see contributions from the Haskell and FP community to this upcoming edition of PLAN-X! Best wishes, -- Torsten ] Call for Papers and Software Demonstrations P L A N - X 2 0 0 7 Programming Language Techniques for XML An ACM SIGPLAN Workshop colocated with POPL 2007 Nice, France -- January 20, 2007 http://www.plan-x-2007.org/ -- PLAN-X 2007 Aim and Scope The XML data model and its associated languages add interesting twists to programming language practice as well as theory. Just like its four predecessors, the PLAN-X 2007 workshop turns the spotlight on how programming languages can embrace, for example, tree-shaped XML data structures, regular expression types extracted from schema descriptions, very small or large XML instances, queries against XML data, and XML transformations. XML reaches deep into all aspects of language design, type systems, compilers, as well as runtimes and PLAN-X 2007 is THE forum to present and discuss novel research work in this area. We invite contributions -- papers as well as software demonstrations -- from members of the programming language, database, theory, and document processing communities and look forward to a workshop in which this diversity of contributions and attendees leads to lively discussion and a fun event. If you are architecting a software system that fuses programming language and XML technology in interesting and innovative ways, please submit a software demonstration proposal to PLAN-X 2007. The workshop program will feature a special demo session. A two-page description of the accepted software demonstrations will be included in the proceedings. PLAN-X 2007 will be held in cooperation with and just after POPL 2007, the 34th ACM SIGPLAN-SIGACT Symposium on Principles of Programming Languages in the Plaza Hotel in Nice, France, on Januar 20, 2007. -- PLAN-X 2007 Topics of Interest Topics of interest include the following (though interesting and/or innovative papers on all aspects of programming languages for XML are welcome): - Design of programming and query languages for XML - Programming in the XML data model itself (e.g., extending XQuery into a full-fledged programming language) - Formal accounts of XML and its processors (based on logic, automata, variants of lambda calculus, etc.) - Compilers and interpreters for XML-aware languages and optimization techniques - Type systems, schema languages, and other constraints (e.g., keys) for tree-shaped data - Tree automata and transducers - Languages and systems that can cope with XML fragments (messages) or very large XML instances (beyond main-memory size) - Programming language glue between browsers, web services, and databases - Pioneering applications of XML-aware language technology -- Proceedings Accepted submissions will be collected to form the informal PLAN-X 2007 proceedings, to be indexed on Michael Ley's DBLP site and distributed at the workshop. The material may thus be published elsewhere at a later date. -- Paper Submission PLAN-X 2007 calls for contributions relevant to the open list of topics sketched above. We explicitly welcome reports on innovative, off-beat, and ''early stage'' approaches as long as the submission reports on original work not published or submitted elsewhere. - Please format your papers according to the ACM guidelines and SIG proceedings templates available at http://www.acm.org/sigs/pubs/proceed/template.html The mandatory submission file format is PDF. - Papers should not exceed 10 pages in length including references and appendices, but shorter abstracts (of, e.g., 2000 words) often suffice and are acceptable as well. - Software demonstration proposals are limited to 2 pages and should include a sketch of the methods you employ as well as a description of what exactly will be demoed. Details on the PLAN-X 2007 paper submission process will be posted on the workshop web site and mailing lists in due course. -- Important Dates - Paper submission: Sun, Oct 1, 2006 - Notification of acceptance: Thu, Nov 23, 2006 - Camera-ready copy due: Sun, Dec 17, 2006 - Workshop: Sat, Jan 20, 2007 -- PLAN-X 2007 Program Committee - Michael Benedikt (Lucent, USA) - Daniela Florescu (Oracle, USA) - Alain Frisch (INRIA Roquencourt, France) - Giorgio Ghelli, Chair (U Pisa, Italy) - Haruo Hosoya (U Tokyo, Japan) - Anders Møller (U Aarhus, Denmark) - Mukund Raghavachari (IBM T.J. Watson Research Center, USA) - Alan Schmitt (INRIA Rhône-Alpes, France) - Sophie Tison (U Lille, France) - Philip Wadler (U Edinburgh, UK) -- PLAN-X 2007 Workshop Chairs - General Chair - Program Chair Torsten Grust Giorgio Ghelli TU München U Pisa Munich, Germany Pisa, Italy grust(a)in.tum.de ghelli(a)di.unipi.it

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rigid variables
by Rodney D Price 20 Jul '06

20 Jul '06

I've gotten this sort of error several times, which mysteriously disappears when I add more functions to the code: storeError.hs:13:38: Couldn't match expected type `a' (a rigid variable) against inferred type `String' `a' is bound by the type signature for `throwError' at <no location info> Expected type: a Inferred type: String In the first argument of `return', namely `msg' In the call (return msg) (This is GHCi.) The code is below. The type variable a can't be bound to String, obviously, but a relative novice like myself has no idea why. Can someone tell me? Thanks, -Rod -- module Store where import Control.Monad.Error import Control.Concurrent.STM data StoreError = Default String instance Error StoreError where noMsg = Default "Store error" strMsg = Default instance MonadError StoreError STM where throwError (Default msg) = return msg

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Re: [Haskell] semantice of seq
by voigt.16734551＠bloglines.com 20 Jul '06

20 Jul '06

--- roconnor(a)theorem.ca wrote: > Do you have an example of use of seq on a function type? (Of course I > don't want to ban it, just change its behaviour.) I don't have any wisdom to offer on how we would want to ban or change the behavior of seq on a function type without using type classes. Nor do I have an example at hand where one absolutely needs to use seq on a function type. But in any case, your request seems to be beside the point, as it comes from the assumption that only seq on function types is dangerous. But that is not true. Polymorphic use of seq can also have dire consequences when the type in question is later instantiated with, say, Int (or whatever). See numerous examples in: http://wwwtcs.inf.tu-dresden.de/~voigt/seqFinal.pdf Ciao, Janis Voigtlaender.

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semantice of seq
by roconnor＠theorem.ca 19 Jul '06

19 Jul '06

Would the problematic semantics of seq be resolved if seq did nothing on function types? That is to say seq (\x -> undefined `asTypeOf` x) y reduced to y and seq (undefined `asTypeOf` id) y also reduced to y -- Russell O'Connor <http://r6.ca/> ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''

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