Ivan Lazar Miljenovic schrieb: > Pros for allowing you to use a custom node type: > * Matches your data better > * No need for extra lookup maps when converting your data to FGL form > > Cons: > * Makes type-sigs uglier/more verbose
Unlabelled graphs with custom node type would have only one type parameter. :-) > * Restricts the ability to optimise That's my question. As far as I know the set of node identifiers in a graph is not contiguous, thus you cannot use Arrays but you must use IntMap or so. > Using Int gives us a fixed-size data type with known good comparison > performance and with a range that should suit most purposes. Replacing IntMap by Map is not much slower, is it? > As an alternative, see how I have Graphalyze create an FGL graph from > [n] and [(n,n,e)]: > http://hackage.haskell.org/packages/archive/Graphalyze/0.9.0.0/doc/html/Data-Graph-Analysis.html#v%3AimportData > > We're also considering using MPTCs or ATs to let you place restrictions > on the label types (when defining a new graph instance). However, > before you again state how you don't want labels, consider this: > > * It's easier to make a labelled graph act as an unlabelled one than the > other way around. Sure, it's the same argument that in MatLab everything is a complex-valued matrix. They even represent Bool by a 1x1 complex-valued matrix. Possible, but clean? From today's viewpoint separation of labelled and unlabelled graphs is additional work, but I'm afraid there will arise problems with this design. Unfortunately, I can't tell them today. > The current "type Node = Int" alias is only there to provide a unique > index type for referencing nodes; the actual Ints don't really represent > the nodes IMHO, the labels do (in conjunction with the index for > colouring, etc.). In your example case of using PkgName (I assume you > mean PackageName or PackageIdentifier?), can you guarantee that each > PkgName value is unique before you go blindly using it (what about > having the same library installed in both the global and user > database?)? Of course you must choose data as key, that is actually a key. But this is not the problem of FGL. And with Node = Int, I also have to choose a key for my dictionary (Map Something Node). In my case I consider packages that are to be installed, so no distinction between globally and locally installed packages. I want really the package name as key. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
