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

From: dan marsden (danmarsden_at_[hidden])
Date: 2008-01-15 15:57:28

Hartmut Kaiser wrote:
>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).

Currently, the most straightforward way to make structural changes to the tree
is at nodes where variants are present. Obviously then switching to a subtree
of a different type is straightforward. Optional and pointers provide limited
scope for eliminating subtrees in a similar way.

As for arbitrary transforms from type A to type B, this is probably the biggest
open question for the library (IMO). Currently local value changes are pretty well supported
within a framework of standard traversals which can be tweaked for certain types.
To what extent the library can / should support traversals in which custom behaviour
is required at the majority of the nodes is an area I'm currently giving thought to.
Ideally I'd like to support at lot more use cases than this first iteration can
manage, as things mature, and I incorporate feedback.

Cheers

Dan




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