- Generics - Haskell.org

ANNOUNCE: Extensible and Modular Generics for the Masses: emgm-0.2
by Sean Leather 30 Jan '09

30 Jan '09

============================================== Extensible and Modular Generics for the Masses ============================================== Extensible and Modular Generics for the Masses (EMGM) is a library for generic programming in Haskell using type classes and a sum-of-products view. ------------ Introduction ------------ emgm-0.2 is the second major release of the EMGM library. A lot of work has been done since the initial release to build a solid set of functions that will allow you to derive the necessary declarations for using EMGM with your datatype. Thus, you don't have to write much code to get started. A great deal of documentation has also been added. There's a comprehensive new entry page for Generics.EMGM that should help one figure out what to do with this library. We plan to publish articles providing more examples as well. With these two improvements, you have no more excuses for not trying it out. Download EMGM and see what you can do, generically! ------------ New Features ------------ Improvements over emgm-0.1 include: * Derive type representation using Template Haskell [1] * Major improvement in documentation with Haddock * bimap function [2] [1] Here is a snippet from the documentation that shows what you save when using TH over manual implementation. > {-# LANGUAGE TemplateHaskell #-} > {-# LANGUAGE MultiParamTypeClasses #-} > {-# LANGUAGE FlexibleContexts #-} > {-# LANGUAGE FlexibleInstances #-} > {-# LANGUAGE OverlappingInstances #-} > {-# LANGUAGE UndecidableInstances #-} > module Example where > import Generics.EMGM > data T a = C a Int > $(derive ''T) The $(derive ''T) declaration in the above example generates the following code: 1. Constructor description declarations (1 per constructor) > conC :: ConDescr > conC = ConDescr "C" 2 [] Nonfix 2. Embedding-projection pair declarations (1 per type) > epT :: EP (T a) (a :*: Int) > epT = EP fromT toT > where fromT (C v1 v2) = v1 :*: v2 > toT (v1 :*: v2) = C v1 v2 3. Rep instance (1 per type) > instance (Generic g, Rep g a, Rep g Int) => Rep g (T a) where > rep = rtype epT (rcon conC (rprod rep rep)) 4. Higher arity instances if applicable (either FRep, FRep2, and FRep3 together, or BiFRep2) > instance (Generic g) => FRep g T where > frep ra = rtype epT (rcon conC (rprod ra rint)) In this case, similar instances would be generated for FRep2 and FRep3. 5. Function-specific instances (1 per type) > instance Rep (Collect Char) Char where > rep = Collect (:[]) [2] EMGM has a new function bimap and its related representation type class BiFRep2: > bimap :: (BiFRep2 Map f) => (a -> c) -> (b -> d) -> f a b -> f c d With bimap, you can do the following in GHCi: *Generics.EMGM Data.Char Prelude> bimap ord chr ('a',65) (97,'A') *Generics.EMGM Data.Char Prelude> bimap (++" So Long!") (const 42) (Right "Earth") Right 42 ------------------- General Information ------------------- Visit the home page: http://www.cs.uu.nl/wiki/GenericProgramming/EMGM ---------------- General Features ---------------- The primary features of EMGM include: * Datatype-generic programming using sum-of-product views * Large collection of ready-to-use generic functions * Included support for standard datatypes: lists, Maybe, tuples * Easy to add support for new datatypes * Type classes make writing new functions straightforward in a structurally inductive style * Generic functions are extensible with ad-hoc cases for arbitrary datatypes * Good performance of generic functions The features of this distribution include: * The API is thoroughly documented with Haddock * Fully tested with QuickCheck and HUnit * Program coverage ensures that all useful code has been touched by tests * Tested on both Mac and Windows systems ------------ Requirements ------------ EMGM has the following requirements: * GHC 6.8.1 - It has been tested with versions 6.8.3 and 6.10.1 * Cabal library 1.2.1 - It has been tested with versions 1.2.4.0 and 1.6.0.1. ----------------- Download & Source ----------------- Use caball-install: cabal install emgm Get the package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/emgm Check out the current source with Subversion: svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/EMGM/trunk Or view it online: https://svn.cs.uu.nl:12443/viewvc/dgp-haskell/EMGM/trunk/ -------- Examples -------- Check out the examples: https://svn.cs.uu.nl:12443/viewvc/dgp-haskell/EMGM/trunk/examples/ -------------- Bugs & Support -------------- Report issues or request features: http://code.google.com/p/emgm/issues/list Discuss EMGM with the authors, maintainers, and other interested persons: http://www.haskell.org/mailman/listinfo/generics ------- Credits ------- The research for EMGM originated with Ralf Hinze. It was extended with work by Bruno Oliveira and Andres Löh. More details of the library functionality were explored by Alexey Rodriguez. We are very grateful to all of these people for the foundation on which this library was built. The current authors and maintainers of EMGM are: * Sean Leather * José Pedro Magalhães * Alexey Rodriguez * Andres Löh

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darcs patch: Add ifdefs around export of :*: and :+: (and 1 more)
by Samuel Bronson 28 Jan '09

28 Jan '09

Tue Jan 27 19:04:06 EST 2009 Samuel Bronson <naesten(a)gmail.com> * Add ifdefs around export of :*: and :+: Tue Jan 27 19:04:27 EST 2009 Samuel Bronson <naesten(a)gmail.com> * Add explicit foralls to GenericT' and GenericM' to allow LHC to parse them

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(CfP) WGP'09: Workshop on Generic Programming Call for Papers
by Patrik Jansson 22 Jan '09

22 Jan '09

Do consider writing papers for WGP'09 (submit by 090510). /Patrik --------------------------- ACM SIGPLAN Workshop on Generic Programming 2009 Edinburgh, UK, August 30, 2009 http://wiki.portal.chalmers.se/cse/WGP09 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 language communities. Generic programming has gradually spread to more and more mainstream languages and is today widely used also in industry. This workshop will bring together leading researchers and practitioners in generic programming from around the world, and feature papers capturing the state of the art in this important area. We welcome contributions on all aspects, theoretical as well as practical, of * adaptive object-oriented programming, * aspect-oriented programming, * concepts (as in the STL / C++ sense) * component-based programming, * generic programming, * meta-programming, * polytypic programming, * programming with modules, * and so on. Organisers: Chair Patrik Jansson, CSE.Chalmers.se co-Chair Sibylle Schupp, STS.TUHH.de Programme Committee: Edwin Brady, U. of St Andrews, Peter Gottschling, TU Dresden Patrik Jansson, Chalmers Chair Barry Jay, U. of T., Sydney Jaakko Järvi, Texas A&M Oleg Kiselyov, FNMOC Andres Löh, Utrecht U. Fritz Ruehr, Willamette U. Sibylle Schupp, TU Hamburg Harburg, Co-Chair Marcin Zalewski, Chalmers, We plan to have formal proceedings, published by the ACM. Submission details Deadline for submission: Sunday 090510 Notification of acceptance: Monday 090601 Final submission due: Tuesday 090616 Workshop: Sunday 090830 Authors should submit papers, in postscript or PDF format, formatted for A4 paper, to the WGP09 EasyChair instance by 10th of May 2009. 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: * Edinburgh, UK 2009 (affiliated with ICFP09) Earlier Workshops on Generic Programming have been held in * Victoria, BC, Canada 2008 (affiliated with ICFP), * Portland 2006 (affiliated with ICFP), * Utrecht 2005 (informal workshop), * Dagstuhl 2002 (IFIP WG2.1 Working Conference), * Nottingham 2001 (informal workshop), * Ponte de Lima 2000 (affiliated with MPC), * Marstrand 1998 (affiliated with MPC). 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 and J Jeuring.

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Proposal #2875: Correct SYB's representation of Char
by José Pedro Magalhães 16 Jan '09

16 Jan '09

Hello all, SYB uses DataRep to represent datatypes: -- | Public representation of datatypes data DataRep = AlgRep [Constr] | IntRep | FloatRep | StringRep | NoRep I believe that StringRep should be CharRep. Note that IntRep is used for the primitive Int and Integer datatypes, FloatRep for Float and Double, and StringRep (apparently) for Char. String, however, is represented as AlgRep [[],(:)]: *Main> dataTypeOf 'p' DataType {tycon = "Prelude.Char", datarep = StringRep} *Main> dataTypeOf "p" DataType {tycon = "Prelude.[]", datarep = AlgRep [[],(:)]} This makes sense, since String is not a primitive datatype. But it causes the apparently wrong behavior: *Main> fromConstr (mkStringConstr (dataTypeOf "a") "ab") :: String "*** Exception: mkStringConstr *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "ab") :: String "*** Exception: constrIndex The correct way of using mkStringConstr is to construct a Char. This, however, only works for strings with a single character: *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "b") :: Char 'b' *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "ab") :: Char *** Exception: gunfold *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "") :: Char *** Exception: gunfold I find this behavior counterintuitive. Therefore I propose to rename StringRep to CharRep and mkStringConstr to mkCharConstr. For backwards compatibility, this entails: * Deprecating mkStringConstr and StringConstr * Deprecating mkStringRep and StringRep * Introducing mkCharConstr and CharConstr * Introducing mkCharRep and CharRep Additionally, due to deprecation warnings, the following have to change as well: * libraries/template-haskell/Language/Haskell/TH/Quote.hs * compiler/utils/Serialized.hs A patch is attached in #2875 ( http://hackage.haskell.org/trac/ghc/ticket/2875) I propose a discussion period of 4 weeks, therefore until the 8th of January. Thanks, Pedro

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ANNOUNCE: zipper-0.1
by Andres Loeh 13 Jan '09

13 Jan '09

zipper-0.1: Generic zipper for systems of recursive datatypes ============================================================= The zipper is a data structure that allows typed navigation on a value. It maintains a subterm as a current point of focus. The rest of the value is the context. Focus and context are automatically updated when navigating up, down, left or right in the value. The term that is in focus can also be modified. This library offers a generic zipper for systems of datatypes. In particular, it is possible to move the focus between subterms of different types, in an entirely type-safe way. This library is built on top of the multirec library, so all that is required to get a zipper for a datatype system is to instantiate the multirec library for that system. Requirements ------------ * GHC 6.8.3 or later * Cabal 1.2.1 or later Download -------- With cabal-install: cabal install zipper Get the package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/zipper Get the source: svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/zipper/trunk Bugs & Support -------------- Report issues, request features, or just discuss the library with the authors, maintainers, and other interested persons at: http://www.haskell.org/mailman/listinfo/generics -- Andres Loeh, Universiteit Utrecht mailto:andres@cs.uu.nl mailto:mail@andres-loeh.de http://www.andres-loeh.de

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ANNOUNCE: multirec-0.2
by Andres Loeh 13 Jan '09

13 Jan '09

multirec-0.2: Generic programming with systems of recursive datatypes ===================================================================== Many generic programs require information about the recursive positions of a datatype. Examples include the generic fold, generic rewriting or the Zipper data structure. Several generic programming systems allow to write such functions by viewing datatypes as fixed points of a pattern functor. Traditionally, this view has been limited to so-called regular datatypes such as lists and binary trees. In particular, systems of mutually recursive datatypes have been excluded. With the multirec library, we provide a mechanism to talk about fixed points of systems of datatypes that may be mutually recursive. On top of this representations, generic functions such as the fold or the Zipper can then be defined. Changelog (changes w.r.t. multirec-0.1) --------------------------------------- * Constructor information and generic show (Generics.MultiRec.Show). * Variants of fold (Generics.MultiRec.FoldAlg) that make the definition of algebras significantly more convenient. * Template Haskell code to generate the boilerplate required to instantiate this library to a system of datatypes. Requirements ------------ * GHC 6.8.3 or later * Cabal 1.2.1 or later Download -------- With cabal-install: cabal install multirec Get the package: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/multirec Get the source: svn checkout https://svn.cs.uu.nl:12443/repos/dgp-haskell/multirec/trunk Bugs & Support -------------- Report issues, request features, or just discuss the library with the authors, maintainers, and other interested persons at: http://www.haskell.org/mailman/listinfo/generics -- Andres Loeh, Universiteit Utrecht mailto:andres@cs.uu.nl mailto:mail@andres-loeh.de http://www.andres-loeh.de

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Help with SYB and ext1T
by Daniel Drienyovszky 17 Dec '08

17 Dec '08

Hi, I'm trying to write a generic nominal abstract syntax library, and I ran into a problem using ext1T. I asked around at #haskell but no one was able to help me, I hope this is not too off topic here. substAbs works just fine by itself, but when I try to combine it with something using ext1T, it stops working. I can't figure out what's the problem with this, am I doing something wrong? *Main> substAbs $ a :\\: a Name "a" (Just 1) :\\: Name "a" (Just 1) *Main> id `ext1T` substAbs $ a :\\: a Name "a" Nothing :\\: Name "a" Nothing Here is my code: >{-# LANGUAGE DeriveDataTypeable #-} > >import Data.Generics > >data Name = Name String (Maybe Int) > deriving (Eq, Show, Data, Typeable) > >refresh (Name s Nothing) = Name s (Just 1) >refresh (Name s (Just i)) = Name s (Just $ i+1) > >data Abs a = Name :\\: a deriving (Eq, Show, Data, Typeable) > >swapName (a,b) x = if a == x then b else > if b == x then a else x > >swap (a,b) = everywhere (mkT $ swapName (a,b)) > >substAbs (n :\\: x) = (m :\\: (x')) > where m = refresh n > x' = swap (n,m) x > >a = Name "a" Nothing >b = Name "b" Nothing Thanks in advance, Daniel.

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Re: Generics
by José Pedro Magalhães 11 Dec '08

11 Dec '08

Hello Simon, Thanks for pointing these out to me. I won't be able to look into this for the next week, but from what I could see so far, #2760 seems easy: copy mkNorepType to mkNoRepType, mark mkNorepType as deprecated and replace usage everywhere to avoid warnings and pass validation. I can submit the patch for this. #2759 has some deeper implications, though. Replacing the FloatConstr Double by FloatConstr Rational might break existing client code (even though it probably wouldn't be too hard to fix it). Additionally, I see that the serializer code in compiler/utils/Serialized.hs would also need changes (it's no longer serializing a Double). But I guess this is also not too problematic... Cheers, Pedro On Fri, Nov 21, 2008 at 13:34, Simon Peyton-Jones <simonpj(a)microsoft.com>wrote: > Jose > > As part of your work on the SYB library, could you spare the time to look > into these two library bug reports? > > http://hackage.haskell.org/trac/ghc/ticket/2759 > http://hackage.haskell.org/trac/ghc/ticket/2760 > > Many thanks > > Simon >

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SYB's StringRep behavior
by José Pedro Magalhães 09 Dec '08

09 Dec '08

Hello, SYB uses DataRep to represent datatypes: -- | Public representation of datatypes > data DataRep = AlgRep [Constr] > | IntRep > | FloatRep > | StringRep > | NoRep > Am I right to believe that StringRep should be CharRep? Note that IntRep is used for the primitives Int and Integer datatypes, FloatRep for Float and Double, and StringRep (apparently) for Char. String, however, is represented as 'AlgRep [[],(:)]': *Main> dataTypeOf 'p' > DataType {tycon = "Prelude.Char", datarep = StringRep} > *Main> dataTypeOf "p" > DataType {tycon = "Prelude.[]", datarep = AlgRep [[],(:)]} This makes sense, since String is not a primitive datatype. But it causes the apparently wrong behavior: > *Main> fromConstr (mkStringConstr (dataTypeOf "a") "ab") :: String > "*** Exception: mkStringConstr > *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "ab") :: String > "*** Exception: constrIndex The correct way of using mkStringConstr is to construct a Char. This, however, only works for strings with a single character: *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "b") :: Char > 'b' > *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "ab") :: Char > *** Exception: gunfold > *Main> fromConstr (mkStringConstr (dataTypeOf 'a') "") :: Char > *** Exception: gunfold > Wouldn't it be more clear if StringRep would be named CharRep and mkStringConstr named mkCharConstr? Thanks, Pedro

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Re: Splitting SYB from the base package in GHC 6.10
by José Pedro Magalhães 13 Nov '08

13 Nov '08

Hello Ian, Yet another haddock documentation fix: the link from Data.Typeable was broken (went to Data.Generics, which is no longer in base; corrected to Data.Data). Thanks, Pedro On Sun, Oct 12, 2008 at 11:39, Ian Lynagh <igloo(a)earth.li> wrote: > > Hi Pedro, > > On Fri, Oct 10, 2008 at 02:31:00PM +0200, José Pedro Magalhães wrote: > > > > I'm attaching some more patches to fix the haddock documentation > (somewhat) > > and the export list of Data.Generics.Instances. > > Thanks; applied to HEAD and 6.10. > > > Thanks > Ian > >

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