Hans van Thiel wrote: > Both CFP and SOE have chapters on trees and there is a standard library > Data.Tree. I expected to find all kinds of functions there, as in > Data.List, but instead the functions are defined as instances of more > general structures.
Well, Data.Tree is not much in use since one almost always needs some special kind of tree and because it's so easy to roll your own. > import Control.Applicative (Applicative(..), (<$>)) > import Data.Foldable (Foldable(foldMap), toList) > import Data.Traversable (Traversable(traverse)) The papers mentioned on the haddock for Data.Traversable are good start. Basically, these concepts are a generalization of the good old "fold" from lists to arbitrary trees (=> Foldable) and from pure functions to general computations (=> Applicative Functors, Traversable). > There is a Zipper http://en.wikibooks.org/wiki/Haskell/Zippers > Ideally I would want a N-ary tree, where the branches are what's > actually the represented data, and so I would like to access it both > from the root and the leaves. In an imperative language I would just add > an up-pointer in each node, but I have no idea how expensive this would > be in Haskell, or if it's necessary at all. Up-pointers won't work in Haskell, you'll need a different approach. Can you elaborate on what your tree looks like and what it stores? Regards, apfelmus _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
