Phlex wrote: > Ketil Malde wrote: >> Identity can be emulated by relatively straightforward means: store all >> planets in a Map indexed by something that is useful as an identifier >> (i.e. stays constant and is unique), and have a Galaxy keep a list of >> identifiers. >> > > So basically you guys are saying I should rethink the data structure > into a relational model instead of sticking to the OO model... I think i > could do this pretty easily. a table would be a map of id to instance > ....then another map for foreign keys, or maybe just as a member of each > data > > Is the relational model a better fit than the object model for > functional programming ?
Well, not really. I mean, if the problem is indeed to store all known planets in the universe, then it's indeed a database in nature and you have to support fine grained operations like delete :: Key -> Database -> Database insert :: Key -> Item -> Database -> Database ... and so on ... (Note that some proposals like changeGalaxies $ changePlanet 0 $ changeName $ const "first" or functional references can be interpreted as keys for 'insert' or 'delete'. I mean that this expression already is the key to look up a planet inside the universe, it's just that this key has a rather unusual type. And that you can compose keys.) But if the problem at hand is perhaps a binary search tree or some other data structure, you can implement many operations without using per-element 'delete' or 'insert' although every operation can in principle be built up from those. Maybe it helps if you elaborate on your concrete problem? Regards, apfelmus _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
