Following on from my last post regarding composites, I've dug out my work on acyclic visitors, and dealing with them alongside composites. I've put these up on a web server for people to have a look at as well. Again I would be interested in comments. http://dah.me.uk/pattern_tl/acyclic_visitor.hpp http://dah.me.uk/pattern_tl/composite_visitor.hpp I've also added some demonstration files to show the sorts of class you might create with the composite and the composite visitors http://dah.me.uk/pattern_tl/NodeBase.h http://dah.me.uk/pattern_tl/VisitorBase.h In use the acyclic visitor is very similar to Alexandrescu's - with only one notable change. I have moved the default visit function into the visitor rather than having it in the visitable. This means that any visitable hierarchy can interact with lots of different visitors, with different default actions and potentially different return types. I find this much more intuitive than the DefaultCatchAll template in Alexandrescu's version. The composite visitors allow you to traverse a given composite in a given order calling the visitor on every node in the tree. I wrote this because of the number of times that you tend to do this particular operation when using composites. You simply need to inject in the composite visitor to turn a visitor into a composite visitor. This results in a slightly odd double-visitation stage where the visitor accepts the visitable, iterates over it and accepts the visitor back again. I generally tend to use this by first setting up a visitor eg: class MyVisitor : public pattern_tl::base_visitor<>, public pattern_tl::visitor<MyNode>; Then creating versions that implement the different ordering strategies as necessary eg: class MyVisitorTopToBottom : public MyVisitor, public pattern_tl::composite_visitor<MyVisitorTopToBottom,MyNode> { }; Then the visiting sequence is initiating by letting the visitor accept the head of the composite: MyVisitorTopToBottom visitor; visitor.accept( head ); Again, any feedback and/or interest would be appreciated. Dave Handley