[Haskell] ANNOUNCE: multirec-0.1

Andres Loeh andres at cs.uu.nl
Fri Oct 31 10:48:48 EDT 2008

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


* 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.


* GHC 6.8.3 or later
* Cabal 1.2.1 or later


With cabal-install:

  cabal install multirec

Get the package:


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:



Andres Loeh, Universiteit Utrecht

mailto:andres at cs.uu.nl     mailto:mail at andres-loeh.de

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