David Roundy wrote:
Hi all,
I'm wanting to create a data structure to hold a directed acyclic
graph (which will have patches represented by edges), and haven't yet
been able to figure out a nice representation. I'd like one that can
be reasoned with recursively, or as closely to recursively as
possible. The problem is one of dependency relations between darcs
patches, and "normally" reduces to a simple tree, with conflict
resolution patches bringing branches of the tree back together. Trees
I know how to handle intuitively and elegantly, but DAGs are a whole
different question.
I looked for papers, and there was one on "an initial-algebra approach
to DAGs" that looked promising, but I'm afraid I wasn't able to fully
understand it, and it is able to describe more complicated DAGs than
I'd like to support.
Anyhow, any suggestions from persons with experience with this sort of
thing would be great. These are getting to be data structures that
are more complicated than anything I'm comfortable with. :(
If you consider a DAG as just an optimized representation for a tree then
you could annotate each node with a Unique and create monadic traversal
functions analogous to tree functions but using a finite map Unique -> r to
memoise the results of traversal so that a node is only traversed once.
Regards, Brian.
--
Logic empowers us and Love gives us purpose.
Yet still phantoms restless for eras long past,
congealed in the present in unthought forms,
strive mightily unseen to destroy us.
http://www.metamilk.com
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