Ivan Miljenovic wrote:
Heinrich Apfelmus wrote:
Yes, the integers are just indexes. Of course, the example with the even integers is a bit silly; but if the integers are actually indexes, then it's conceptually cleaner to make them abstract, i.e.
data Node -- constructors are not exported
and provide combinators to operate on these abstract indexes, including a corresponding Data.Graph.Inductive.NodeMap module.
I'd like to see such an abstract Node type, because then the library will provide all operations I need. It took me some time to figure out how to best use Int as indexes in my example code; an abstract Node type and a good NodeMap module would have made my life much easier.
I'm not sure I understand what you're saying here: first you said you wanted to be able to specify a vertex type, now you're saying that you don't want to know what the vertex type even is (except that it's some abstract Node type)? Whilst this would make graph usage safer/more robust, this seems to contradict your earlier arguments...
I'd be happy with either one. :) In both cases, I want to specify a custom vertex type. I can either do that directly if the library permits, though I think the solution with associated types is too cumbersome to be useful for my make example. Or I get an abstract Node type and the library provides just the right functions that make it easy to manage a custom vertex type myself. I had hoped that the Data.Graph.Inductive.NodeMap module provides this, which it doesn't. In other words, the abstractness of Node forces the library to provide a well-designed set of functions to work with them, and that's what I'm after. In my make example, I spent the most time thinking about how to manage the Int nodes, finally settling with Data.Map.findIndex , and I prefer the library to think about that for me.
Darn, I meant
data Graph node a b = Graph { internal :: Graph Int a b, nodes :: Map Int a }
The idea is to use Ints internally and only store a loose association to the custom vertex type. In particular, no Map a Int is required, only from Int to a . Now, I realize that the other way round is required as well for querying the context of a node in a graph.
What's the point of that useless node type parameter then? And how does the nodes map differ from just getting the graph label?
You're right, I now realize that this design doesn't work. But you asked for wishes, so I wished for something. ;) Regards, Heinrich Apfelmus -- http://apfelmus.nfshost.com