Re: [Spirit-devel] [boost] RFC Generic data structure traversal / manipulation library

[Hartmut K. <har...@gm...>]

> I'm posting an early version of a library for manipulating 
> hierarchical data structures,  for  example the parse trees 
> that are produced by Spirit2. The library enables traversals, 
> and local modifications of complex data structures, without 
> the need to implement large amounts of repetitive traversal 
> code. The library is in a very early state, but has a pretty 
> large introduction and quick start guide, which (hopefully) 
> will help get people started with the library. Formal 
> documentation is unfortunately non-existent at this point.
> 
> The library is based on techniques from the Haskell 
> community, links to relevant papers are provided in the documentation.
> 
> The library is intended to play well with the rest of Boost, 
> it already contains support for structures built with 
> Boost.Optional and Boost.Variant, and Boost.Fusion, and will 
> support other Boost libraries in future releases. The library 
> makes heavy use of function objects, and is intended to work 
> with Boost.Lambda, Phoenix, and other function object 
> libraries in Boost.

I second the expressed opinion that this library is a very important piece
of work and I'm looking forward to having it available. 

IIUC, the traversal library is designed to help traversing arbitrary data
structures and to apply local _value_ changes. My question is:
Is the used concept extensible in a way allowing for _structural_ changes of
the traversed data structure? This would make it usable for tree
transformations, which would be especially interesting if used with
Spirit.Qi (parsing) and Spirit.Karma (generation).

Regards Hartmut