October 2008 - Generics

ANNOUNCE: multirec-0.1
by Andres Loeh 31 Oct '08

31 Oct '08

multirec: 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. We expect that the library will be especially interesting for compiler writers, because ASTs are typically systems of mutually recursive datatypes, and with multirec it becomes easy to write generic functions on ASTs. The library is based on ideas described in the paper: Alexey Rodriguez, Stefan Holdermans, Andres Löh, Johan Jeuring Generic programming with fixed points for mutually recursive datatypes Technical Report, Universiteit Utrecht http://www.cs.uu.nl/research/techreps/repo/CS-2008/2008-019.pdf Features -------- * Generalizes the fixed point view from single, regular datatypes to systems of recursive datatypes. * Includes detailed examples: generic fold and generic compos, the latter in the style of Björn Bringert, Arne Ranta A pattern for almost compositional functions ICFP 2006 The Zipper and generic rewriting for systems of datatypes will be released soon as separate libraries that build on multirec. * The generic compos functions do not require the user to modify their existing systems of datatypes. * In its current form, this library does not support nested 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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Re: syb changes (Re: base-3 vs base-4 (Was: Breakage with 6.10))
by José Pedro Magalhães 13 Oct '08

13 Oct '08

Hello Ian, I'm attaching patches that add a link to the new wiki from the haddock of syb (and change the maintainer to generics(a)haskell.org) Thanks, Pedro On Mon, Oct 13, 2008 at 11:39, José Pedro Magalhães <jpm(a)cs.uu.nl> wrote: > Hello, > > I created a new wiki page for SYB which also contains some more detailed > information on the changes for 6.10: > http://www.cs.uu.nl/wiki/bin/view/GenericProgramming/SYB > > > Thanks, > Pedro >

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Re: Splitting SYB from the base package in GHC 6.10
by José Pedro Magalhães 10 Oct '08

10 Oct '08

Hello, On Sun, Oct 5, 2008 at 15:40, Claus Reinke <claus.reinke(a)talk21.com> wrote: > >The following "dubious" instances are now in the syb package (in the > >Data.Generics.Instances module): DataType TyCon TypeRep Handle ThreadId > >StablePtr (a -> b) (IO a) (ST s a) (STM a) (IORef a) (TVar a) (MVar a). > All > >the other instances are in the base package, Data.Data module. > > Contrary to that list, 'Data (a->b)' is still in Data.Data? > Oops, my mistake. Thanks for noticing! Attaching patches. Thanks, Pedro

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Re: Splitting SYB from the base package in GHC 6.10
by José Pedro Magalhães 04 Oct '08

04 Oct '08

Hello Ian, On Mon, Sep 22, 2008 at 21:54, Ian Lynagh <igloo(a)earth.li> wrote: > > I'm a little lost as to exactly what changes you want. Can you send a > darcs patch against the base and syb repos please?: > http://darcs.haskell.org/ghc-6.10/packages/base/ > http://darcs.haskell.org/ghc-6.10/packages/syb/ > Currently everything is in the syb package. I'm attaching patches to 4 repositories that split SYB between the syb and base packages. (It's my first time doing this so I hope all is fine, but if not just let me know.) Basically, a new module Data.Data in base contains the previous Data.Generics.Basics and most of the instances from Data.Generics.Instances. Other changes are: On Mon, Sep 15, 2008 at 13:28, José Pedro Magalhães <jpm(a)cs.uu.nl> wrote: > > - Ratio has to be fixed to have a consistent instance: either it's seen > as an abstract datatype (therefore with undefined gunfold) or a gfoldl has > to be defined matching its gunfold; > > Ratio had its gfoldl defined to match its gunfold. Since GHC.Ratio exports the constructor (:%), I guess Ratio cannot be considered abstract. > - Complex should have its derived instance restored (or otherwise a > manual instance with a proper gfoldl); > > Complex had its derived instance restored. > - Other places that have to be changed: > - The Data instance of Data.Array should be moved from > Data.Generics.Instances into Array, to avoid syb dependency; > > This was not done, since I am unsure if it would break some sort of Hugs compatibility. If the instance for Array is in Data.Data (note that it is not an orphan anymore), then it's provided independently of where the Array comes from. If it would be in Data.Array, then Hugs would have to provide an instance in its Array library too. > - The imports of SYB in the following modules should be fixed to avoid > bringing into scope all the instances: > > ./containers/Data/IntMap.hs > ./containers/Data/IntSet.hs > ./containers/Data/Map.hs > ./containers/Data/Sequence.hs > ./containers/Data/Set.hs > ./containers/Data/Tree.hs > ./network/Network/URI.hs > ./packedstring/Data/PackedString.hs > > This was not done, given the discussion in [1] regarding instance visibility and orphans. The following "dubious" instances are now in the syb package (in the Data.Generics.Instances module): DataType TyCon TypeRep Handle ThreadId StablePtr (a -> b) (IO a) (ST s a) (STM a) (IORef a) (TVar a) (MVar a). All the other instances are in the base package, Data.Data module. Ian, do you think this could be incorporated in any possible upcoming beta versions/release candidates before the final release? I did some sanity checking but it would be good if a wider audience could test it. Thanks, Pedro [1] http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9929/focus=27

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