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