- Generics - Haskell.org

make type witnesses 'phi ix' persistent?
by Sebastian Menge 20 Sep '10

20 Sep '10

Hi I am playing around with the zipper package. I wrote some helper functions that allow for a more convenient description of the zipper state as addresses in the basic form "path@term". The types and auxiliary functions are given below. Now I would like to make these addresses "persistent". I want to write them to disk somehow, and reconstruct them in a later session. But to reconstruct addresses, I have to create the type witnesses from the serialization, e.g.: serialize :: forall phi ix . (Fam phi, El phi ix) => phi ix -> String serialize MyWitness1 = "MyWitness1" serialize MyWitness2 = "MyWitness2" But deserialize wont work: deserialize :: String -> phi ix -- <--- impossible deserialize "MyWitness1" = MyWitness1 deserialize "MyWitness2" = MyWitness2 Is there _any_ way to get this going ? Any dirty hacks are also appreciated ;) Thanks, Sebastian. PS here come the relevant types and functions (not tested, just copy'n'pasted from my sources) -- more convenient zipper states data Address phi s t = Address { typerep :: phi s , value :: s , pathrep :: phi t , path :: Path } type Path = [Int] type Nav phi ix= (Loc phi I0 ix -> Maybe (Loc phi I0 ix)) -- convert int-paths to navigations tonav :: Path -> Nav phi ix tonav (path) = foldl (>=>) return (map tonav' path) where tonav' 0 = down tonav' i = tonav' (i-1) >=> right -- lookup an address lookup::(Fam phi, Zipper phi (PF phi), EqS phi) => Address phi s t -> t lookup a = (pathrep a, path a) @@ (typerep a, value a) -- explicit lookup on pairs. idea: "path@term" (@@) :: forall phi ix1 ix2. (Fam phi, Zipper phi (PF phi), EqS phi) => (phi ix2,Path) -> (phi ix1,ix1) -> ix2 (@@) (q,path) (p,e) = case (tonav path $ enter p e) of (Just l :: (Maybe (Loc phi I0 ix1))) -> focus q l Nothing -> error "invalid path" -- helper that extracts the focus focus :: forall phi ix xi. (EqS phi) => phi ix -> (Loc phi I0 xi) -> ix focus p (Loc q (I0 x) cs) = case eqS p q of Just Refl -> x _ -> error "focus: types dont match"

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type constructor genericity with regular
by Jan Christiansen 15 Sep '10

15 Sep '10

Hi, I want to define a function which is generic for all unary type constructors using the regular package. More precisely, I want to define a function like the following, which replaces every polymorphic component by the position of the component in the generic representation. shape :: (Regular f, Shape (PF f)) => f a -> f [Bool] Is it correct that it is not possible to implement a function like this using regular? Or do I miss something? I have implemented the function by using different representation types K, I and so forth that take an additional argument. Furthermore I have added an additional type to mark the polymorphic component. Thanks, Jan

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ANNOUNCE: grammar-combinators 0.1 (initial release): A parsing library of context-free grammar combinators
by Dominique Devriese 09 Sep '10

09 Sep '10

Copying this announcement to generics(a)haskell.org. The grammar-combinators library may interest some people here, because it uses Multirec pattern functors throughout, to abstract a grammar from its semantics. More details in the paper we are submitting to PADL 2011 [1]. Dominique [1]: http://projects.haskell.org/grammar-combinators/#background The grammar-combinators library is a parsing library employing a novel grammar representation with explicit recursion. The library features much of the power of a parser generator like Happy or ANTLR, but with the library approach and most of the benefits of a parser combinator library. Grammars and grammar algorithms are defined in a functional style. The library currently has the following features: * Grammar specified completely in Haskell using an elegant syntax * Grammar algorithms implemented in a functional style (no fresh identifiers), with elegant and meaningful types. * Multi-backend: use the same grammar with a Packrat, Parsec or UUParse parser * Grammar transformations: use left-recursive grammars directly thanks to a powerful grammar transformation library, featuring the left-corner left-recursion removal transform, a uniform version of the classic Paull left-recursion removal, and various smaller transformations (dead-branch removal, dead non-terminal removal, consecutive epsilon combination, selective unfolding etc.). * Grammar utility functions: printing of grammars, FIRST-set calculation, reachability analysis of non-terminals, etc. * Compile-time transformations (using Template Haskell), given a suitable definition of the grammar. This is currently limited to a certain set of transformations. The library is currently not intended for mainstream use. Its API is relatively stable, but performance needs to be looked at further. We are submitting a paper about the ideas behind this library to PADL 2011. A draft is linked on the project's website. More information: * Project website: http://projects.haskell.org/grammar-combinators/ * Tutorial: http://projects.haskell.org/grammar-combinators/tutorial.html * Hackage: http://hackage.haskell.org/package/grammar-combinators All comments welcome! Dominique PS. The documentation on hackage currently doesn't build because of (seemingly) a Hackage dependency problem during the build [1]. Compiling and generating the documentation locally should work fine. A version of the docs is available on the project's webpage as a temporary replacement [2]. Footnotes: [1] http://www.haskell.org/pipermail/libraries/2010-September/014168.html [2] http://projects.haskell.org/grammar-combinators/docs/index.html

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darcs patch: update package description with new upper limit on the...
by Antoine Latter 08 Sep '10

08 Sep '10

1 patch for repository http://code.haskell.org/syb: Mon Sep 6 12:56:43 CDT 2010 Antoine Latter <aslatter(a)gmail.com> * update package description with new upper limit on the base dependency With this change I seem to be able to compile with GHC HEAD. The new Cabal issue wanrings directed us to use the new testing infrastructure, but that warning is left unadressed.

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SYB with base >= 4.3
by Kathleen Fisher 04 Sep '10

04 Sep '10

Hi, I'd like to install the SYB package, but my base library is 4.3.0.0 (the version in the current GHC HEAD). The constraints on syb installation require base version < 4.3. Is there a new version somewhere that compiles against 4.3 that I could install? Kathleen

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Compile issue with multirec TH
by Dominique Devriese 23 Jun '10

23 Jun '10

Hi, I'm having a compile issue with multirec TH. Upon investigation, it seems the same problem occurs in the compilation of one of the examples in the multirec distribution: domi@arial:/tmp> wget -q http://hackage.haskell.org/packages/archive/multirec/0.4.1/multirec-0.4.1.t… domi@arial:/tmp> tar xzf multirec-0.4.1.tar.gz domi@arial:/tmp> cd multirec-0.4.1/examples domi@arial:/tmp/multirec-0.4.1/examples> ghc --make ASTTHUse.hs [1 of 2] Compiling AST ( AST.hs, AST.o ) [2 of 2] Compiling ASTTHUse ( ASTTHUse.hs, ASTTHUse.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package multirec-0.4.1 ... linking ... done. ASTTHUse.hs:31:2: GADT pattern match in non-rigid context for `Tag' Probable solution: add a type signature for `to' In the pattern: Tag L C K f0 In the pattern: L Tag L C K f0 In the definition of `to': to Expr L Tag L C K f0 = Const f0 domi@arial:/tmp/multirec-0.4.1/examples> ghc --version The Glorious Glasgow Haskell Compilation System, version 6.12.1 Can you please tell me if this is a known problem and if so, if there is a workaround? Thanks in advance for your help! Dominique

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Workshop on Generic Programming (WGP) 2010 Final Call for Papers
by Bruno Oliveira 06 Jun '10

06 Jun '10

Dear all, This is the final reminder that the deadline for WGP submission is in one week (13th of June). See the call for papers below: ====================================================================== CALL FOR PAPERS WGP 2010 6th ACM SIGPLAN Workshop on Generic Programming Baltimore, Maryland, US Sunday, September 26th, 2010 http://osl.iu.edu/wgp2010 Collocated with the International Conference on Functional Programming (ICFP 2010) ====================================================================== Goals of the workshop --------------------- Generic programming is about making programs more adaptable by making them more general. Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters. In contrast with normal programs, the parameters of a generic program are often quite rich in structure; for example they may be other programs, types or type constructors, class hierarchies, or even programming paradigms. Generic programming techniques have always been of interest, both to practitioners and to theoreticians, and, for at least 20 years, generic programming techniques have been a specific focus of research in the functional and object-oriented programming communities. Generic programming has gradually spread to more and more mainstream languages, and today is widely used in industry. This workshop brings together leading researchers and practitioners in generic programming from around the world, and features papers capturing the state of the art in this important area. We welcome contributions on all aspects, theoretical as well as practical, of * polytypic programming, * programming with dependent types, * programming with type classes, * programming with (C++) concepts, * generic programming, * programming with modules, * meta-programming, * adaptive object-oriented programming, * component-based programming, * strategic programming, * aspect-oriented programming, * family polymorphism, * object-oriented generic programming, * and so on. Organizers ---------- Co-Chair Bruno C. d. S. Oliveira, Seoul National University Co-Chair Marcin Zalewski, Indiana University Programme Committee ------------------- Alley Stoughton, Kansas State University Andrei Alexandrescu, Facebook Bruno C. d. S. Oliveira (Co-Chair), Seoul National University Doug Gregor, Apple Gilad Bracha, I am a Computational Theologist Emeritus Magne Haveraaen, Universitetet i Bergen Marcin Zalewski (Co-Chair), Indiana University Neil Mitchell, Standard Chartered Ralf Lämmel, University of Koblenz-Landau Shin-Cheng Mu, Academia Sinica Thorsten Altenkirch, University of Nottingham Ulf Norell, Chalmers University Important Information --------------------- We plan to have formal proceedings, published by the ACM. Submission details Deadline for submission: Sunday 2010-06-13 Notification of acceptance: Monday 2010-07-12 Final submission due: Tuesday 2010-07-27 Workshop: Sunday 2010-09-26 Authors should submit papers, in postscript or PDF format, formatted for A4 paper, to the WGP09 EasyChair instance by 13th of June 2010. The length should be restricted to 12 pages in standard (two-column, 9pt) ACM format. Accepted papers are published by the ACM and will additionally appear in the ACM digital library. History of the Workshop on Generic Programming ---------------------------------------------- This year: * Baltimore, Maryland, US 2010 (affiliated with ICFP10) Earlier Workshops on Generic Programming have been held in * Edinburgh, UK 2009 (affiliated with ICFP09) * Victoria, BC, Canada 2008 (affiliated with ICFP), * Portland 2006 (affiliated with ICFP), * Ponte de Lima 2000 (affiliated with MPC), * Marstrand 1998 (affiliated with MPC). Furthermore, there were a few informal workshops * Utrecht 2005 (informal workshop), * Dagstuhl 2002 (IFIP WG2.1 Working Conference), * Nottingham 2001 (informal workshop), There were also (closely related) DGP workshops in Oxford (June 3-4 2004), and a Spring School on DGP in Nottingham (April 24-27 2006, which had a half-day workshop attached). Additional information: The WGP steering committee consists of J Gibbons, R Hinze, P Jansson, J Jarvi, J Jeuring, B Oliveira, S Schupp and M Zalewski

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WGP 2010 Second Call for Papers
by Bruno Oliveira 02 May '10

02 May '10

====================================================================== CALL FOR PAPERS WGP 2010 6th ACM SIGPLAN Workshop on Generic Programming Baltimore, Maryland, US Sunday, September 26th, 2010 http://osl.iu.edu/wgp2010 Collocated with the International Conference on Functional Programming (ICFP 2010) ====================================================================== Goals of the workshop --------------------- Generic programming is about making programs more adaptable by making them more general. Generic programs often embody non-traditional kinds of polymorphism; ordinary programs are obtained from them by suitably instantiating their parameters. In contrast with normal programs, the parameters of a generic program are often quite rich in structure; for example they may be other programs, types or type constructors, class hierarchies, or even programming paradigms. Generic programming techniques have always been of interest, both to practitioners and to theoreticians, and, for at least 20 years, generic programming techniques have been a specific focus of research in the functional and object-oriented programming communities. Generic programming has gradually spread to more and more mainstream languages, and today is widely used in industry. This workshop brings together leading researchers and practitioners in generic programming from around the world, and features papers capturing the state of the art in this important area. We welcome contributions on all aspects, theoretical as well as practical, of * polytypic programming, * programming with dependent types, * programming with type classes, * programming with (C++) concepts, * generic programming, * programming with modules, * meta-programming, * adaptive object-oriented programming, * component-based programming, * strategic programming, * aspect-oriented programming, * family polymorphism, * object-oriented generic programming, * and so on. Organizers ---------- Co-Chair Bruno C. d. S. Oliveira, Seoul National University Co-Chair Marcin Zalewski, Indiana University Programme Committee ------------------- Alley Stoughton, Kansas State University Andrei Alexandrescu, Facebook Bruno C. d. S. Oliveira (Co-Chair), Seoul National University Doug Gregor, Apple Gilad Bracha, I am a Computational Theologist Emeritus Magne Haveraaen, Universitetet i Bergen Marcin Zalewski (Co-Chair), Indiana University Neil Mitchell, Standard Chartered Ralf Lämmel, University of Koblenz-Landau Shin-Cheng Mu, Academia Sinica Thorsten Altenkirch, University of Nottingham Ulf Norell, Chalmers University Important Information --------------------- We plan to have formal proceedings, published by the ACM. Submission details Deadline for submission: Sunday 2010-06-13 Notification of acceptance: Monday 2010-07-12 Final submission due: Tuesday 2010-07-27 Workshop: Sunday 2010-09-26 Authors should submit papers, in postscript or PDF format, formatted for A4 paper, to the WGP09 EasyChair instance by 13th of June 2010. The length should be restricted to 12 pages in standard (two-column, 9pt) ACM format. Accepted papers are published by the ACM and will additionally appear in the ACM digital library. History of the Workshop on Generic Programming ---------------------------------------------- This year: * Baltimore, Maryland, US 2010 (affiliated with ICFP10) Earlier Workshops on Generic Programming have been held in * Edinburgh, UK 2009 (affiliated with ICFP09) * Victoria, BC, Canada 2008 (affiliated with ICFP), * Portland 2006 (affiliated with ICFP), * Ponte de Lima 2000 (affiliated with MPC), * Marstrand 1998 (affiliated with MPC). Furthermore, there were a few informal workshops * Utrecht 2005 (informal workshop), * Dagstuhl 2002 (IFIP WG2.1 Working Conference), * Nottingham 2001 (informal workshop), There were also (closely related) DGP workshops in Oxford (June 3-4 2004), and a Spring School on DGP in Nottingham (April 24-27 2006, which had a half-day workshop attached). Additional information: The WGP steering committee consists of J Gibbons, R Hinze, P Jansson, J Jarvi, J Jeuring, B Oliveira, S Schupp and M Zalewski

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Re: [Hs-Generics] Re: Add everywhereM' to Data.Generics.Schemes
by Neil Mitchell 25 Apr '10

25 Apr '10

Hi Matthias, I started writing an email, but decided a blog post would be a better place to put down my thoughts on everywhere': http://neilmitchell.blogspot.com/2010/04/dangerous-primes-why-uniplate-does… > This said, if I understand your last post correctly, the use of everywhereM' > would be a bug here in your eyes. Do you agree? Because I don't think so. It's possible to use everywhere' correctly, but not trivial. Using descend it's trivial to get right, which is much safer. Read the blog post for my best thoughts why. > I > haven't done a lot of testing yet, but each case where a replacement has to > be performed works as expected. And even if it's not a bug, do you suggest > to drop everywhereM' and use uniplate instead, just to play it safe? I recommend to everyone they drop whatever generics solution they are using and switch to Uniplate :-) [If Uniplate can express what you want - it's one of the least powerful generics libraries - but gets almost all the common uses] I think using descend (from Uniplate) or compos (from Compos paper), or writing a descend/compos operator for SYB, is the right way to go. It's a nicer primitive, and it's perfectly definable in most generics frameworks. I think everywhere' is a bad primitive in any generics framework. Thanks, Neil > > Am 18.04.2010 09:38 schrieb Neil Mitchell: >> >> Hi, >> >> I thought a lot about everywhere' when writing uniplate. I have an >> equivalent of everywhere (transform), but no transform'. In the end I >> decided that it was virtually impossible to use everywhere' correctly, >> and that almost every call of everywhere' was either somewhere an >> everywhere would have worked equally well, or a bug. I then went >> through all the Haskell source code I could find, found about 6 calls >> to everywhere', and all of them would have performed the same job as >> everywhere. >> >> So, my suggestion is that everywhereM' probably isn't very useful, but >> descend/descendM (or compos) is a useful top-down traversal scheme. >> >> Thanks, Neil > >

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Re: Add everywhereM' to Data.Generics.Schemes
by José Pedro Magalhães 18 Apr '10

18 Apr '10

Hi Maciej, Data.Generics.Schemes is now on the syb package, and I'm its maintainer. But I'm not so sure it is wise to start adding more traversal schemes of this form, since there might be many of them: if we include everywhereM', we certainly have to include the bottom-up everywhereM too. Then there are the possible Applicative variants, etc... In general, since these traversal functions are small and everywhere and everywhere' already show the pattern of how to write them, maybe it's best that they are defined by the user, unless there is some general consensus that they would be widely useful. Cheers, Pedro On Mon, Apr 12, 2010 at 20:56, Maciej Podgurski < maciej.podgurski(a)googlemail.com> wrote: > Hello, > > as an analogue to everywhere', I suggest adding everywhereM' to > Data.Generics.Schemes. The implementation would be > > everywhereM' :: Monad m => GenericM m -> GenericM m > everywhereM' f x = do { x' <- f x; > gmapM (everywhereM' f) x' } > > > Best wishes, > > Maciej > _______________________________________________ > Libraries mailing list > Libraries(a)haskell.org > http://www.haskell.org/mailman/listinfo/libraries >

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