August 2005 - Haskell

Re: [Haskell] Partially applied type class functions
by Paul Govereau 06 Aug '05

06 Aug '05

Thanks alot for the clarifications. If I understand correctly, I ran into the monomorphism restriction because of the constraint on the type variable. The Haskell report says this in Section 4.5.5: In addition, the constrained type variables of a restricted declaration group may not be generalized in the generalization step for that group. Thus, this is perfectly fine: > f1 :: Int -> a -> String > f1 i a = "" > x = let g = f1 1 in (g 1, g "a") Whereas this definition, with the additional (Show a) constraint, runs in to the monomorphism restriction: > f2 :: Show a => Int -> a -> String > f2 i a = show a > y = let g = f2 1 in (g 1, g "a") No instance for (Num [Char]) arising from the literal `1' at Syntax.lhs:16:24 Probable fix: add an instance declaration for (Num [Char]) In the first argument of `g', namely `1' In the definition of `y': y = let g = f2 1 in (g 1, g "a") I think my original program was a case similar to this last one. Thanks again for the quick response. Paul On Aug 05, Roberto Zunino wrote: > Paul Govereau wrote: > [snip] > >>instance AbSyn Constraint where > >> subst e n constr = > >> let sub = subst e n -- :: AbSyn a => a -> a > >> in case constr > >> of Zero expr -> Zero (sub expr) > >> AndL cs -> AndL (sub cs) > > > >It looks sort of like sub is being monomorphised -- or something? > > I think you just hit the monomorphism restriction. For the details, see: > http://www.haskell.org/onlinereport/decls.html - Sect. 4.5.5 > http://haskell.org/hawiki/MonomorphismRestriction > > Possible solutions for your specific case are: > > 1) add an explicit type signature for sub > > let sub :: AbSyn a => a -> a > sub = subst e n > in ... > > 2) eta-expand sub, so its definition becomes a function binding > > let sub c = subst e n c > in ... > > > Regards, > Roberto Zunino. >

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Partially applied type class functions
by Paul Govereau 06 Aug '05

06 Aug '05

Hello, I have encountered a type error that I find quite puzzling. I would appreciate it if someone could help me understand what is going wrong. Here is the program: > data Expr = Var String | Const Int > data Constraint = Zero Expr | AndL Constraint > class AbSyn a where > subst :: Expr -> String -> a -> a > instance AbSyn Expr where subst e n expr = expr > instance AbSyn Constraint where > subst e n constr = > let sub = subst e n -- :: AbSyn a => a -> a > in case constr > of Zero expr -> Zero (sub expr) > AndL cs -> AndL (sub cs) GHC 6.4 (as well as Hugs March 2005) produces this error: Couldn't match `Constraint' against `Expr' Expected type: Constraint Inferred type: Expr In the application `sub cs' In the first argument of `AndL', namely `(sub cs)' If I replace the last line with this one, everything is fine: AndL cs -> AndL (subst e n cs) It looks sort of like sub is being monomorphised -- or something? Thanks for having a look, Paul

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unsafePerformIO and optimizations
by Wolfgang Jeltsch 06 Aug '05

06 Aug '05

Hello, http://haskell.org/ghc/docs/latest/html/libraries/base/ System.IO.Unsafe.html#v%3AunsafePerformIO talks about what optimizations you should disable if you apply unsafePerformIO to an action which contains side effects. These are: * inlining of functions which call unsafePerformIO * common subexpression elimination (on the module which contains the unsafePerformIO application, if I understand correctly) * let-floating Alas, the documentation is very terse, in my opinion, and I don't understand these things fully. First, what is the problem with inlining a function call? Say, I have a function f defined as follows: f :: Char -> () f c = unsafePerformIO (putChar c) If inlining is allowed, the expression f '*' becomes unsafePerformIO (putChar '*'). Is this a problem? Or is inlining dangerous in other situations? On the other hand, I can see that inlining non-functions could cause harm. Say I have something like this: u :: () u = unsafePerformIO (putChar '*') Now, inlining u would transform (u,u) to (unsafePerformIO (putChar '*),unsafePerformIO (putChar '*')) which could result in putChar '*' being executed multiple times. So why does the library documentation only talk about disabling inlining of functions? I understand that common subexpression elimination could cause harm. It could transform the expression (unsafePerformIO (putChar '*),unsafePerformIO (putChar '*')) to let u = unsafePerformIO (putChar '*') in (u,u), couldn't it? This would result in the I/O action be performed at most once which is not what was intended. But couldn't the same thing also happen if I use the expression (f '*',f '*'), probably in a different module? Does this mean that I have to use -fno-cse not only in the module which contains the unsafePerformIO application but also in every other module which uses unsafePerformIO indirectly via f or functions using f? Does let-floating only have to be disabled in the module which uses unsafePerformIO? Say, I have f defined as above and have the following definition in a module different from the one f is defined in: g :: Int -> () g n = f '*' Couldn't it be that the asterisk is output only once instead of every time, g is called? I would be thankful for any help. Best regards, Wolfgang

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ANN: Haskell bindings to OpenLDAP
by John Goerzen 06 Aug '05

06 Aug '05

Hello, The first preliminary (but working!) version of my bindings to OpenLDAP from Haskell is now available from: darcs get --partial http://darcs.complete.org/ldap-haskell This implements searching, adding, modifying, and deleting data in LDAP directories. As such, it fully supports the base operations that are most important to LDAP programs. It doesn't yet support all the features in the C API, and also doesn't yet support lazy reads of the search result set. These things will be coming. Comments, questions, and patches are welcome. -- John

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RE: [Haskell] ANNOUNCE: Haddock version 0.7
by Simon Marlow 05 Aug '05

05 Aug '05

On 05 August 2005 13:57, Adrian Hey wrote: > Does the linking to source still work with this version? > I can't get it to work anyway, but maybe I'm doing something > wrong. All I get for each module is a link to whatever URL > I specify, but without the actual source module name(path) > attached at the end. The semantics of the -s option were changed. Unfortunately, I forgot to document the change. See this message for details: http://www.haskell.org//pipermail/glasgow-haskell-users/2005-May/008394. html Cheers, Simon

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Last call for registration: GPCE'05 (deadline 2 september)
by Eelco Visser 05 Aug '05

05 Aug '05

LAST CALL for REGISTRATION (Deadline Sep 02) >>>>>>>>>>> On-site registration will NOT be available ---------------------------------------------------------------------- 4th International Conference on Generative Programming and Component Engineering (GPCE'05) Sep 29 - Oct 1, 2005, Tallinn (Estonia) http://www.gpce.org/05 Sponsored by ACM SIGPLAN, in cooperation with ACM SIGSOFT co-located with ICFP'05 and TFP'05 ---------------------------------------------------------------------- IMPORTANT DATES * Sep 02, 2005: LATE REGISTRATION DEADLINE * Sep 27-28, 2005: GPCE workshops and tutorials * Sep 29 - Oct 1, 2005: GPCE papers and demos It is recommended that any changes or additions to existing registrations be done before Sep 02. ---------------------------------------------------------------------- SCOPE. Generative and component approaches have the potential to revolutionize software development in a similar way as automation and components revolutionized manufacturing. Generative Programming (developing programs that synthesize other programs), Component Engineering (raising the level of modularization and analysis in application design), and Domain-Specific Languages (elevating program specifications to compact domain-specific notations that are easier to write and maintain) are key technologies for automating program development. ---------------------------------------------------------------------- 3 INVITED SPEAKERS: * Oscar Nierstrasz: Object-oriented Reengineering Patterns * Oege de Moor: The AspectBench Compiler for AspectJ * Bernd Fischer: Certifiable Program Generation 25 TECHNICAL PAPERS 2 DEMONSTRATIONS: * Developing Dynamic and Adaptable Applications with CAM/DAOP: a Virtual Office Application * Metamodeling made easy - MetaEdit+ 2 TUTORIALS T1: Multi-stage Programming in MetaOCaml (Presenters: W.Taha, C.Calcagno) T2: Implementing Domain-Specific Modelling Languages and Generators (Presenter: R.Pohjonen) 3 WORKSHOPS W1: Seventh Young Researchers Workshop (Organizers: D.R.Dechow, D.Foetsch, S.Kiebusch, S.Perugini, M.J.Rutherford, D.Shestakov) W2: Second MetaOCaml Workshop (Organizers: K.Swadi, W.Taha) W3: Graph and Model Transformations Workshop (Organizers: G.Karsai, G.Taentzer) ---------------------------------------------------------------------- PROGRAM COMMITTEE Chairs: * Robert Glück (U. of Copenhagen) * Michael Lowry (NASA) Members: * Don Batory (U. of Texas, USA) * Ira Baxter (Semantic Designs) * Cristiano Calcagno (Imperial College) * Prem Devanbu (U. of California at Davis) * Ulrich Eisenecker (U. of Leipzig) * Tom Ellman (Vassar College) * Robert Filman (NASA) * Zhenjiang Hu (U. of Tokyo) * Patricia Johann (Rutgers U.) * John Launchbury (Galois) * Anne-Françoise Le Meur (U. of Sci. and Tech. Lille) * Hong Mei (Peking U.) * Nicolas Rouquette (NASA) * William Scherlis (CMU) * Yannis Smaragdakis (Georgia Inst. of Tech.) * Walid Taha (Rice U.) * Todd Veldhuizen (Chalmers U. of Tech.) ORGANIZING COMMITTEE General Chair * Eugenio Moggi (Genova U.) Publicity Chair: * Eelco Visser (Utrecht U.) Workshops and Tutorials Chairs * Jeff Gray (U. of Alabama at Birmingham) * Andrew Malton (Waterloo U.) Local Arrangements Chair * Tarmo Uustalu (Inst. of Cybernetics, Tallinn) ----------------------------------------------------------------------

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ST/STRef vs. IO/IORef
by Srinivas Nedunuri 05 Aug '05

05 Aug '05

Hello, I have some code that manipulates STRefs within the ST monad. All good and fine, until I come across some computation that uses lets say IO and everything skids to a halt. At this point I have 3 choices: 1. Define a ST State Transformer monad and do all my previous ST computations in that 2. convert all subsequent ST computations into IO computations using stToIO 3. stop using the ST monad and do everything in the IO monad I was wondering what advice folks had. In particular, what are the disadvantages to doing everything in the IO monad - ie why even bother with the ST monad? Any help appreciated cheers

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IFL'05 CFP and Registration reminder
by Andrew Butterfield 04 Aug '05

04 Aug '05

Dear colleagues, just a reminder that the registration deadline for IFL'05 is fast approaching (7th Aug.) - see https://www.cs.tcd.ie/ifl05/registration.php for details = Call for Papers/Participation = Announcement and Call for Papers for the 17th International Workshop on the Implementation and Application of Functional Languages (IFL'05) September 19th-21st, 2005, Dublin, Ireland. Website: http://www.cs.tcd.ie/ifl05 E-mail: ifl05(a)cs.tcd.ie == Scope and Topics == The IFL workshops form a tradition that has lasted for nearly two decades. The aim of these workshops is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. They provide an open forum for researchers who wish to present and discuss new ideas and concepts, work in progress, preliminary results, etc. related primarily but not exclusively to the implementation and application of functional languages. Topics of interest include, but are not limited to * language concepts * type checking * compilation techniques * generic programming techniques * (abstract) interpretation * automatic program generation * (abstract) machine architectures * formal aspects * array processing * concurrent/parallel programming * concurrent/parallel program execution * heap management * runtime profiling * performance measurements * debugging and tracing * verification * tools and programming techniques Papers on applications demonstrating the suitability of novel ideas in any of the above areas and contributions on related theoretical work are also welcomed. The change of the workshop name adding the term "application", introduced in 2004, is to reflect the broader scope IFL has gained over recent years. == Contributions == Prospective authors are encouraged to submit papers to be published in the draft proceedings (published as a technical report of the Department of Computer Science of the University of Dublin) and to give presentations at the workshop. All contributions must be written in English, conform to the Springer-Verlag LNCS series format, and not exceed 16 pages. http://www.springer.de/comp/authors/index.html or http://www.springeronline.com/ sgw/cda/frontpage/0,11855,5-164-2-72376-0,00.html Papers must be submitted by August 26th as postscript or pdf files through the workshop web page at http://www.cs.tcd.ie/ifl05/. All participants who give presentations at the workshop are invited to submit revised versions of their papers for the post-workshop proceedings. They will be refereed by the program committee according to normal conference standards, and will be published by Springer as part of the Lecture Notes in Computer Science series. === Programme Committee ===== * Matthias Blume, Toyota Technological Institute at Chicago, USA * Andrew Butterfield, /(Chair)/ Trinity College Dublin, Ireland. * Clemens Grelck, University of Lübeck, Germany. * Zoltán Horváth, Eötvös Loránd University, Hungary. * Frank Huch, University of Kiel, Germany. * Joe Kiniry, National University of Ireland Dublin, Ireland. * Hans-Wolfgang Loidl, Ludwig-Maximilians-University Munich, Germany. * Frédéric Loulergue, University of Paris XII, Val de Marne, France. * Simon Marlow, Microsoft Research, Cambridge, UK * Marco T. Morazán, Seton Hall University, NJ, USA. * Joseph Morris, Dublin City University, Ireland. * Barak A. Pearlmutter, National University of Ireland Maynooth, Ireland. * Rinus Plasmeijer, Radboud Universiteit Nijmegen, Netherlands. * Peter Thiemann, University of Freiburg, Germany. * Phil Trinder, Heriot-Watt University, UK. * Germán Vidal, Technical University of Valencia, Spain. == Important Dates == * Aug 7th, 2005 Registration deadline * Aug 26th, 2005 Submission deadline for draft proceedings * Sep 19th, 2005 Workshop starts in the morning * Sep 20th, 2005 Afternoon excursion and banquet dinner * Sep 21st, 2005 Workshop ends in the evening * Nov 7th, 2005 Submission deadline for post-refereeing process * Dec 16th, 2005 Notification of acceptance/rejection * Feb 3rd, 2006 Camera-ready papers due == Further Information == Website: http://www.cs.tcd.ie/ifl05 E-mail: ifl05(a)cs.tcd.ie

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IFL'05: CFP and Registration reminder
by Andrew Butterfield 04 Aug '05

04 Aug '05

Dear colleagues, just a reminder that the registration deadline for IFL'05 (Aug 7th) is fast approaching - see https://www.cs.tcd.ie/ifl05/registration.php for details = Call for Papers/Participation = Announcement and Call for Papers for the 17th International Workshop on the Implementation and Application of Functional Languages (IFL'05) September 19th-21st, 2005, Dublin, Ireland. Website: http://www.cs.tcd.ie/ifl05 E-mail: ifl05(a)cs.tcd.ie == Scope and Topics == The IFL workshops form a tradition that has lasted for nearly two decades. The aim of these workshops is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. They provide an open forum for researchers who wish to present and discuss new ideas and concepts, work in progress, preliminary results, etc. related primarily but not exclusively to the implementation and application of functional languages. Topics of interest include, but are not limited to * language concepts * type checking * compilation techniques * generic programming techniques * (abstract) interpretation * automatic program generation * (abstract) machine architectures * formal aspects * array processing * concurrent/parallel programming * concurrent/parallel program execution * heap management * runtime profiling * performance measurements * debugging and tracing * verification * tools and programming techniques Papers on applications demonstrating the suitability of novel ideas in any of the above areas and contributions on related theoretical work are also welcomed. The change of the workshop name adding the term "application", introduced in 2004, is to reflect the broader scope IFL has gained over recent years. == Contributions == Prospective authors are encouraged to submit papers to be published in the draft proceedings (published as a technical report of the Department of Computer Science of the University of Dublin) and to give presentations at the workshop. All contributions must be written in English, conform to the Springer-Verlag LNCS series format, and not exceed 16 pages. http://www.springer.de/comp/authors/index.html or http://www.springeronline.com/ sgw/cda/frontpage/0,11855,5-164-2-72376-0,00.html Papers must be submitted by August 26th as postscript or pdf files through the workshop web page at http://www.cs.tcd.ie/ifl05/. All participants who give presentations at the workshop are invited to submit revised versions of their papers for the post-workshop proceedings. They will be refereed by the program committee according to normal conference standards, and will be published by Springer as part of the Lecture Notes in Computer Science series. === Programme Committee ===== * Matthias Blume, Toyota Technological Institute at Chicago, USA * Andrew Butterfield, /(Chair)/ Trinity College Dublin, Ireland. * Clemens Grelck, University of Lübeck, Germany. * Zoltán Horváth, Eötvös Loránd University, Hungary. * Frank Huch, University of Kiel, Germany. * Joe Kiniry, National University of Ireland Dublin, Ireland. * Hans-Wolfgang Loidl, Ludwig-Maximilians-University Munich, Germany. * Frédéric Loulergue, University of Paris XII, Val de Marne, France. * Simon Marlow, Microsoft Research, Cambridge, UK * Marco T. Morazán, Seton Hall University, NJ, USA. * Joseph Morris, Dublin City University, Ireland. * Barak A. Pearlmutter, National University of Ireland Maynooth, Ireland. * Rinus Plasmeijer, Radboud Universiteit Nijmegen, Netherlands. * Peter Thiemann, University of Freiburg, Germany. * Phil Trinder, Heriot-Watt University, UK. * Germán Vidal, Technical University of Valencia, Spain. == Important Dates == * Aug 7th, 2005 Registration deadline * Aug 26th, 2005 Submission deadline for draft proceedings * Sep 19th, 2005 Workshop starts in the morning * Sep 20th, 2005 Afternoon excursion and banquet dinner * Sep 21st, 2005 Workshop ends in the evening * Nov 7th, 2005 Submission deadline for post-refereeing process * Dec 16th, 2005 Notification of acceptance/rejection * Feb 3rd, 2006 Camera-ready papers due == Further Information == Website: http://www.cs.tcd.ie/ifl05 E-mail: ifl05(a)cs.tcd.ie

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WCFLP 2005: Call for Participation
by Michael Hanus 03 Aug '05

03 Aug '05

CALL FOR PARTICIPATION WCFLP 2005 International Workshop on Curry and Functional Logic Programming An ACM SIGPLAN sponsored workshop at ICFP 2005 Tallinn, Estonia September 29, 2005 WWW: http://www.informatik.uni-kiel.de/~mh/wcflp2005 The aim of this workshop is to bring together researchers interested in Curry, related functional logic languages, and general aspects of integrating declarative programming paradigms. It promotes the cross-fertilizing exchange of ideas and experiences among researches and students from the different communities interested in the foundations, applications, and combinations of high-level, declarative programming languages and related areas. REGISTRATION Registration for the workshop is through the TFP/ICFP/GPCE site: http://www.cs.ioc.ee/tfp-icfp-gpce05/ PROGRAMME 9.15: Opening 9.30: Claudio Ochoa, Josep Silva and German Vidal: Lightweight Program Specialization via Dynamic Slicing 10.00: Rafael Caballero: A Declarative Debugger of Incorrect Answers for Constraint Functional-Logic Programs 11.00: Julio Marino and Jose Maria Rey: Adding Constraints to Curry via Flat Guards 11.30: Sonia Estevez Martin and Rafael del Vado Virseda: Designing an Efficient Computation Strategy in CFLP(FD) Using Definitional Trees 12.00: Jesus M. Almendros-Jimenez: Constraint Logic Programming over Sets of Spatial Objects 14.30: Michael Hanus: A Generic Analysis Environment for Declarative Programs 15.00: J. Guadalupe Ramos, Josep Silva and German Vidal: An Offline Partial Evaluator for Curry Programs 15.30: Sebastian Fischer: A Functional Logic Database Library 16.30: Bernd Braßel and Frank Huch: Translating Curry To Haskell 17.00: Emilio Gallego and Julio Marino: An Overview of the Sloth2005 Curry System 17:30: Individual system demonstrations, closing ----------------------------------------------------------------------

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