August 2006 - Haskell

Re: [Haskell] thread-local variables
by Frederik Eaton 08 Aug '06

08 Aug '06

> Furthermore, can we move this thread from the Haskell mailing list > (which should not have heavy traffic) to either Haskell-Café, or > the libraries list? Sure, moving to haskell-cafe. Frederik -- http://ofb.net/~frederik/

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"strange" behavior of Implicit Parameters
by Eike Scholz 08 Aug '06

08 Aug '06

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

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deriving DeepSeq and deep strict fields proposals (Re[2]: [Haskell-cafe] How can we detect and fix memory leak due to lazyness?)
by Bulat Ziganshin 08 Aug '06

08 Aug '06

Hello Ki, Tuesday, August 8, 2006, 6:34:51 AM, you wrote: > Unfortunately seq and the strict data declaration is not helpful in general. > They are only helpful on base values such as Int or Bool. > What they do is just making sure that it is not a thunk. > That is if it was a list it would just evaluate to see the cons cell > but no further. > Someone wrote a deepSeq module for forcing deep evaluation, which is it was a proposal to add deepSeq to the language itself (just allow to automatically derive it by compiler, for example). we can add another proposal of implementing deep strict fields: data T = C !![Int] -- Best regards, Bulat mailto:Bulat.Ziganshin@gmail.com

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Contexts on Data Declarations
by Iavor Diatchki 05 Aug '06

05 Aug '06

Hello, I was just looking at the details of how contexts on datatypes work in Haskell'98 and I noticed the following. The report states that the context on a particular constructor should contain all those predicates that mention only variables that are in the fields of the constructor. This wording does not scale very well to mult-paramater type classes, and indeed Hugs (20050308) and GHC (6.4.1) do different things. Here is an example: > class C a b > > data C a b => T a b = Mk a According to Hugs, Mk :: a -> T a b, which follows the report: the constarint is not added because it mentions a variable, b, which is not in the fields of Mk. According to GHC, however, Mk :: C a b => a -> T a b, which also makes sense if we interpret the report to mean: "all those predicates that constrain a variable in the fields of the constructor". I know that contexts on data types are not a very popular part of the Haskell design, but it would be nice to be consistent. To me it seems that GHC's interpretation is the correct one. -Iavor PS: Appologies if this is fixed in later versions of Hugs, I don't have a newer version at the moment to try it out.

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Call for Posters, APLAS 2006 (in Sydney, in November)
by Eijiro Sumii 04 Aug '06

04 Aug '06

CALL FOR POSTER PRESENTATIONS The Fourth ASIAN Symposium on Programming Languages and Systems (APLAS 2006) November 8-10, 2006 University of New South Wales, Sydney, Australia Deadline for Abstracts: September 11, 2006 APLAS 2006 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). Links that may be useful for preparing good posters include: - http://www.kumc.edu/SAH/OTEd/jradel/Poster_Presentations/PstrStart.html - http://www.siam.org/siamnews/general/poster.htm REGISTRATION: Each presenter should e-mail a 1-2 page abstract in PDF or PostScript to the poster chair (sumii AT ecei DOT tohoku DOT ac DOT jp) by September 11th, 2006. The program of the poster session will be announced by September 22nd, 2006. We hope to accommodate every poster, but may restrict presentations (based on relevance and interest to the community) for the limitation of space. We may also need to cancel the session if there are too few presentations. IMPORTANT DATES: - 1-2 page abstract submission deadline September 11, 2006 - notification September 22, 2006 - conference November 8-10, 2006 CONTACT: For questions or requests, please contact the APLAS 2006 poster chair, Eijiro Sumii (sumii AT ecei DOT tohoku DOT ac DOT jp).

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CUFP: Call for Participation
by Kathleen Fisher 03 Aug '06

03 Aug '06

[ Apologies for multiple postings; please forward to potentially interested parties ] CALL FOR PARTICIPATION Registration is now open! http://regmaster2.com/conf/icfp2006.html CUFP 2006 THE THIRD COMMERCIAL USERS OF FUNCTIONAL PROGRAMMING WORKSHOP "Functional programming as a means, not an end" Portland, Oregon, USA September 21st 2006 Co-located with ICFP Functional languages have been under academic development for over 25 years, and are still proving to be very fertile ground for programming language research. Consequently, most of the development focus of these languages is driven by academic and theoretical questions. More recently, however, functional languages have been very successfully used in commercial, industrial, and government settings, as well as in the open-source community. In these settings, the advantages of functional languages have provided dramatic leverage. The goal of CUFP is to act as a voice for commercial users of functional programming languages and technology. It aims to help functional programming become increasingly viable as a technology for use in the commercial, industrial, governmental, and open-source space by providing a forum for FP professionals to share their experiences and ideas, whether business, management or engineering. It also aims to enable the formation and strengthening of relationships and alliances that further the commercial use of functional languages. Providing user feedback to language designers and implementors is not a primary goal of the workshop, though it will be welcome if it occurs. Program ------- The meeting will last a full day, with a mix of invited and submitted presentations, plus discussion sessions. Confirmed speakers include: *Richard Cleis* on embedding PLT Scheme in device controllers for the Air Force. *Roope Kaivola* on his work for Intel constructing functional models and the verifying hardware against such models using reFLect, Intel's reflective functional language. *J. Garrett Morris* on Aetion Technologies and how they use Haskell to rapidly prototype new systems and to develop generic software foundations that enable them to extend to new markets quickly. *Erik Stenman* on Kreditor, a company that successfully sells invoicing services to web shops; all of their software is written in Erlang. *Clifford Besher* on his work at Linspire on using functional languages for all of their tools and his efforts to promote the use of Haskell/FP within the open source community. *Steve Sims* on Reactive Systems, a company that licenses an automated testing tool for embedded software, mostly written in SML. *Yaron Minsky* on Jane Street Capital, a proprietary trading company, whose trading systems and infrastructure are all implemented in OCaml. There will be no published proceedings, as the meeting is intended to be more a discussion forum than a technical interchange. See http://www.galois.com/cufp/ for more information, including the most recent schedule information. Program Committee ----------------- Andy Adams-Moran. adams-moran at galois.com (Co-Chair) Mike Ashley. mashley at beckman.com Matthias Felleisen. matthias at ccs.neu.edu Kathleen Fisher. kfisher at research.att.com (Chair) Jim Grundy. jim_grundy at ichips.intel.com John Hughes. rjmh at cs.chalmers.se Stephen Weeks. sweeks at sweeks.com Ulf Wiger. ulf.wiger at ericsson.com

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CFP for Practical Aspects of Declarative Languages: 9th Symposium
by Simon Marlow 03 Aug '06

03 Aug '06

[ posting on behalf of Gopal Gupta <gupta(a)utdallas.edu> ] ====================================================================== CALL FOR PAPERS Ninth International Symposium on Practical Aspects of Declarative Languages 2007 (PADL '07) http://www.informatik.uni-kiel.de/~mh/padl07 Nice, France January 14-15, 2007 Co-located with ACM POPL'07 ====================================================================== Declarative languages build on sound theoretical foundations to provide attractive frameworks for application development. These languages have been successfully applied to a wide array of different real-world situations, including database management, active networks, software engineering, web applications, decision support systems, or music composition. New developments in theory and implementation have opened up new application areas. At the same time, the application 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 often 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 practioners 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 and their impact on applications; * evaluation of implementation techniques on practical applications; * novel uses of declarative languages in the classroom; and * practical experiences PADL 07 welcomes new ideas and approaches pertaining to applications and implementation of declarative languages, and is not limited to the scope of the past eight PADL symposia. PADL 07 will be co-located with the ACM POPL. ---------------------------------------------------------------------- IMPORTANT DATES AND SUBMISSION GUIDELINES Abstract Submission: August 30, 2006 Paper Submission: September 3, 2006 (strict) Notification: October 2, 2006 Final Manuscript: October 22, 2006 Symposium: January 14-15, 2007 All submissions must be original work written in English. Submissions must be unpublished and not submitted for publication elsewhere. Work that already appeared in unpublished or informally published workshops proceedings may be submitted. Authors should submit an electronic copy of the full paper (written in English) in Postscript (Level 2) or PDF via the web page of PADL 07. 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, submissions should adhere to the LNCS paper formatting guidelines. 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 programm 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 may make multiple awards. ---------------------------------------------------------------------- PROGRAM COMMITTEE Matthias Blume (Toyota Technological Institute at Chicago, USA) Manuel Chakravarty (University of New South Wales, Australia) Marc Feeley (University of Montreal, Canada) Hai-Feng Guo (University of Nebraska at Omaha, USA) Gopal Gupta (University of Texas at Dallas, USA) Michael Hanus (University of Kiel, Germany, Chair) Michael Leuschel (University of Duesseldorf, Germany) Simon Peyton Jones (Microsoft Research, Cambridge, UK) Enrico Pontelli (New Mexico State University, USA) German Puebla (Technical University of Madrid, Spain) Francesca Rossi (University of Padova, Italy) Michel Rueher (University of Nice, France) Christian Schulte (Royal Institute of Technology, Sweden) Zoltan Somogyi (University of Melbourne, Australia) Peter Stuckey (University of Melbourne, Australia) Doaitse Swierstra (Utrecht University, The Netherlands) Simon Thompson (University of Kent, UK) Pascal Van Hentenryck (Brown University, USA) German Vidal (Technical University of Valencia, Spain) ---------------------------------------------------------------------- CONTACTS: For information about papers and submissions, please contact the Program Chair: Michael Hanus PC Chair - PADL 2007 Institut fuer Informatik University of Kiel D-24098 Kiel, Germany Email: mh(a)informatik.uni-kiel.de For other information about the conference, please contact: Gopal Gupta Department of Computer Science University of Texas at Dallas Dallas, TX, U.S.A. Email: gupta(a)utdallas.edu Sponsored by: COMPULOG Americas (http://www.cs.nmsu.edu/~complog) ----------------------------------------------------------------------

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Re: [Haskell] Monadic parser combinators with logging
by Harald ROTTER 03 Aug '06

03 Aug '06

Thanks for the hint, I will try to implement the suggested monadic structure. As for the MonadState declaration: If I put instance MonadState PState Parser then ghci complains: Illegal instance declaration for 'MonadState PState Parser' (The instance type must be of form (T a b c) where T is not a synonym, and a,b,c are distict type variables) In the instance declaration for 'MonadState PState Parser' I found out that invoking ghci with "-fglasgow-exts" solves the issue nut I have to admit that I do not really understand what's so special about this instance declaration to make it require the extensions. Harald. Andrew Pimlott <andrew(a)pimlott.net To: Harald ROTTER <harald.rotter(a)sagem.com> > cc: haskell(a)haskell.org Subject: Re: [Haskell] Monadic parser combinators with logging 03.08.2006 02:54 Delivered date: 03.08.2006 02:54 On Wed, Aug 02, 2006 at 10:52:14AM +0200, Harald ROTTER wrote: > newtype Parser a = Parser { runParser :: (PState -> [(a, PState)])} > > as the parsing monad with the Parser state "PState" that contains the > remaining input after matching and possibly some additional user defined > state elements. I want to add logging such that the application of every > element parser/parser combinator gets recorded in a string. In the end I > want to print out the trace of all encountered parsers for successful and > for failed matches. > > I tried to use the WriterT transformer to add a writer monad on top of the > Parser monad but for failed matches (i.e. runParser gives []) the log is > also "lost" since WriterT gives a monad of "m (a,w)". Excellent observation! The order in which you apply monad transformers matters. "WriterT w Parser" keeps a separate output for each branch of the parser. If you stare at the definition of (>>=) for WriterT, you'll see why this must be so. Or, as you did, you can just look at the type. > What I would look for is "(m a, w)". Hmm, that looks like (if m is Parser) a parser plus some output. I think you'd rather have an answer plus some output, ie "([(a, PState)], w)". Hint: Consider newtype Parser m a = Parser { runParser :: (PState -> m [(a, PState)])} where m is a Monad. > How can I make the Parser monad given above an instance of MonadState ? (I > always get kind errors ...) Did you switch up the order of parameters or something? I don't get any error using instance MonadState Int Parser where ... Andrew

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Monadic parser combinators with logging
by Harald ROTTER 03 Aug '06

03 Aug '06

Dear all, I am a Haskell newbie and I try to find my way through Monad territory. Actually I am studying the non-deterministic monadic parser combinators as descibed by Hutton and Meijer. Although I find this very elegant and concise I seem to have problems extending the parser monads. I use newtype Parser a = Parser { runParser :: (PState -> [(a, PState)])} as the parsing monad with the Parser state "PState" that contains the remaining input after matching and possibly some additional user defined state elements. I want to add logging such that the application of every element parser/parser combinator gets recorded in a string. In the end I want to print out the trace of all encountered parsers for successful and for failed matches. I tried to use the WriterT transformer to add a writer monad on top of the Parser monad but for failed matches (i.e. runParser gives []) the log is also "lost" since WriterT gives a monad of "m (a,w)". What I would look for is "(m a, w)". Finally, my questions: What is the most elegant way to achieve logging parsers ? Can I use the standard transformes or do I need to write my own transformers ? How can I make the Parser monad given above an instance of MonadState ? (I always get kind errors ...) Any hints are really appreciated. Thank you Harald Rotter.

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ANN: TextRegexLazy-0.56, (=~) and (=~~) are here
by Chris Kuklewicz 02 Aug '06

02 Aug '06

Announcing: TextRegexLazy version 0.56 Where: Tarball from http://sourceforge.net/projects/lazy-regex darcs get --partial [--tag=0.56] http://evenmere.org/~chrisk/trl/stable/ License : BSD, except for DFAEngine.hs which is LGPL (derived from CTK light) Development/unstable version is at: darcs get [--partial] http://evenmere.org/~chrisk/trl/devel/ This is the version that has eaten John Meacham's JRegex library and survived to become strong. Thanks John! It now compiles against the posix regexp provided by the c library and the pcre library, in addition to the "full lazy" and the "DFA" backends. All 4 backends can accept regular expressions given as String and as ByteString. All 4 backends can run regular expressions against String and ByteString. In particular, the PosixRE and PCRE can run very efficiently against ByteString. (Though the input for the PosixRE needs to end in a \NUL character for efficiency). So there are 4*2*2 = 16 ways to use to provide input to this library. And the RegexContext class has at least 11 instances that both (=~) and (=~~) can target. So that is 4*2*2*11*2 = 352 things you can do with this library! Get your copy today! To run with cabal before 1.1.4 you will need to comment out the "Extra-Source-Files:" line in the TextRegexLazy.cabal file. The Example.hs file: > {-# OPTIONS_GHC -fglasgow-exts #-} > import Text.Regex.Lazy > import Text.Regex.Full((=~),(=~~)) -- or DFA or PCRE or PosixRE > > main = let b :: Bool > b = ("abaca" =~ "(.)a") > c :: [MatchArray] > c = ("abaca" =~ "(.)a") > d :: Maybe (String,String,String,[String]) > d = ("abaca" =~~ "(.)a") > in do print b > print c > print d This produces: > True > [array (0,1) [(0,(1,2)),(1,(1,1))],array (0,1) [(0,(3,2)),(1,(3,1))]] > Just ("a","ba","ca",["b"]) You can also use makeRegex and makeRegexOpts to compile and save a regular expression which will be used multiple times. Each of the 4 backends has a separate "Regex" data type with its own option types. For low level access, the WrapPCRE and WrapPosix modules expose a typesafe layer around the c libraries. You can query the "getVersion :: Maybe String" to see if the have been compiled into the library. It may be possible to use WrapPCRE and the UTF8 option flags to do unicode regex matching with PCRE. ( The Full and DFA backends use the Haskell unicode Char already ). Adding new types to String/ByteString is a matter of adding instances to the existing classes. Feedback and comments of any length is welcome. -- Chris Kuklewicz

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