On 10/08/10 05:24, Gordon Woodhull wrote:
Sorry for the slow response - been on vacation offline.
No problem ;)
I wonder if Dan Marsden's Traversal library would solve this out of
the box?
http://boost-spirit.com/dl_docs/traversal/html/traversal/introduction.html
Oh nice link, I didn't knew that :o
The way I would solve it is to create an adapter that makes a Proto
tree look like a graph... Like Boost.Graph, Metagraph is designed to
allow adapting any metadata that is already graphlike to have a graph
API. (This wasn't the right approach for MSM because there's nothing
in those tables that immediately answers "what are the edges for this
vertex?")
If there is interest, I could probably pull this together pretty
quickly, as Proto already has such an expressive API. Then we'd
immediately have inefficient implementations of DFS & BFS and I could
see if there's a good way to factor out the color map stuff to make it
speedy.
We're looking at two challenge in Proto :
-> traversing the AST type at compile-time to apply meta-function onto
tree node
-> traversing the AST value at run-time to apply function onto tree node
The main API debate when it comes to traversals is "visitors or
iterators?" Currently metagraph takes the visitor approach from
Boost.Graph, which are more general and expressive, but iterators are
often more convenient. Any opinions here? AFAIK we don't have
coroutines or continuations in C++ metaprogramming to make the
inversion of control easier. ;-)
I can't say much but, for example here is my current use-cases:
- walkign through a proto AST to apply a visitor onto node/leaf : turn
the AST on array into the same AST with pointer element before evaluation
- turning the AST into a DAG
- applying a visitor performing osme kind of reduction on the tree
startign form the leaf to evaluate the value of the AST in a given point
of evaluation
- for a given assign node (lhs = rhs) check if the lhs data address is
somewhere in the terminal of rhs. This is basically our trickiest
runtime algorithm in nt2 that helps us detetcing alias in expression
without having ppl using alias(x) function.
- detecting pattern in the AST (like a+b*c) and repalce all of them,
recurisvely into another (here by madd(a,b,c)). It's currently done with
special grammar and it's maybe better to do it like this but we never know.
I'm from the old guard w/r to tree, so I'm mostly thinking in visitor.
But if you care to show me how iterators can be used, I'm open to
suggestion.
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