2010/7/24 Ivan Lazar Miljenovic

Once again cc-ing -cafe; Immanuel, can you please do "reply to all" rather than just "reply" in GMail? :p

Oh, yes I forgot - sorry! Thanks for all the valuable infos :-) Immanuel

Immanuel Normann writes:

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2010/7/24 Ivan Lazar Miljenovic

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CC-ing haskell-cafe again:

Immanuel Normann writes:

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2010/7/24 Ivan Lazar Miljenovic

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Some of my lnodes in the graph have by construction unique labels and I want to lookup the lnode from a graph given only the label of that lnode.

Well, from my understanding NodeMap doesn't do what you want, since it assumes that _all_ of the node labels are unique

I wouldn't bother when NodeMap maps also non-unique labels to single nodes, because I only lookup nodes with unique labels, e.g. assume my label are of the form data Label = Unique String | Multi Label

I'm of the suspicion that using NodeMaps in this fashion will have problem when considering nodes with the same label (even if you don't explicitly use it for those nodes), as NodeMap seems to assume that node labels are unique.

For example, mkNode assumes node labels are unique.

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Furthemore, the way of using it seems to be analogous of how one would use a State monad rather than for actual interactive use throughout.

Could you elaborate this further, please.

http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-... and

http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-...

If you just want a mapping from labels to nodes, you may be better off using your own custom Map (and maybe even defining a new graph type that has such a Map as part of it).

The successor to FGL-5.x (whatever we'll end up calling it) will allow you to have custom node types rather than using Ints. However, this will not work for you in this situation.

The node type is just an _index_ type, analogous to the actual hash value in a hash{map,array} (as opposed to the value which has the hashing function applied upon it). It's there to provide a unique identifier for a particular node. Arguably, an abstract type would be even better as an Int as it will prevent you from doing silly things like adding node indices together, but that's beside the point.

If you wish to find a node with a specific label, try using something like gsel: http://hackage.haskell.org/packages/archive/fgl/5.4.2.3/doc/html/Data-Graph-...

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com