On Wed, Jun 04, 2008 at 11:11:58PM +0200, apfelmus wrote:
Ian Lynagh wrote:
Also, it's actually the derivative of Forest, not Tree, right? Which is why toTree can lose information, here the b and c trees: Data.Tree.Zipper> toTree (Loc (Node 'a' []) [Node 'b' []] [Node 'c' []] []) Node {rootLabel = 'a', subForest = []} This feels a little scary to me.
I should expand on that: I wonder if toTree should return Maybe (Tree a) which returns Nothing if either sibling is non-empty.
Yes. A zipper for a tree would have to carry the value a around.
It would actually simplify the datastructure; rather than data TreeLoc a = Loc { tree :: Tree a -- ^ The currently selected tree. , lefts :: Forest a -- ^ Siblings on the left, closest first. , rights :: Forest a -- ^ Siblings on the right, closest first. , parents :: [(Forest a, a, Forest a)] -- ^ The contexts of the parents for this location. } deriving (Read,Show,Eq) we could have just data TreeLoc a = Loc { tree :: Tree a -- ^ The currently selected tree. , parents :: [(Forest a, a, Forest a)] -- ^ The contexts of the parents for this location. } deriving (Read,Show,Eq) where the Forests are now children of the parent nodes, rather than their siblings. The cost is that you now can't represent forests nicely. Thanks Ian